Oncogene (2003) 22, 2160–2171 & 2003 Nature Publishing Group All rights reserved 0950-9232/03 $25.00 www.nature.com/onc

Ligand-activated Ahr signaling leads to disruption of nephrogenesis and altered Wilms’ tumor suppressor mRNA splicing

M Hadi Falahatpisheh and Kenneth S Ramos*

Center for Environmental and Rural Health, Texas A & M University, College Station, TX, USA

The aryl hydrocarbon receptor (Ahr), a member of the nuclear-binding protein activity has been implicated in large basic helix–loop–helix (bHLH) and PAS homology anomalies of kidney development (Avner, 1993). Wilms’ domain superfamily, is a highly conserved transcriptional tumor suppressor gene (wt1) has been characterized as a regulator involved in mammalian development. In the key regulatory gene in mesenchymo-epithelial transition present study, a murine metanephros organ culture system and differentiation during nephrogenesis. wt1 encodes a was employed to evaluate the role of the Ahr signaling in Cis2-His2 zinc finger DNA-binding protein that med- nephrogenesis in vitro. Ahr and Wilms’ tumor suppressor iates transcriptional repression/activation of target (wt1) mRNAs were detected by in situ hybridization and genes by binding DNA sequences containing the 50- 0 RT–PCR during the course of renal development. GCGGGGGCG-3 as well as (TCC)n repeats. Both Treatment with 3 lm BaP, a hydrocarbon ligand of Ahr, transcriptional repression and activation depend on the inhibited glomerulogenesis and branching morphogenesis architecture of the promoter, and involve distinct of metanephric kidneys. Deficits in the epithelialization of domains of the WT1 protein (Drumond et al., 1992; mesenchymal cells were evidenced by inhibition of the Wang et al., 1992). formation of podocyte foot processes and glomerular The wt1 gene contains 10 exons spanning approxi- basement membranes. Hydrocarbon treatment markedly mately 50 kb (Gessler et al., 1992). As a result of induced ÀKTS wt1 splice variants, although total wt1 alternative RNA splicing, multiple proteins are gener- mRNA levels remained unchanged. A significant decrease ated ranging in molecular weight from 49 to 62 kDa in total WT1 protein was observed by both immunocyto- (Scharnhorst et al., 1999). One alternative splicing event chemistry and Western analysis in cultures challenged results in inclusion/exclusion of exon 5 (7exon 5), a with BaP compared to controls. Comparison of meta- sequence that encodes for a stretch of 17 amino acids nephric cultures from Ahr+/+ and AhrÀ/À mice showed within the N-terminus of the four zinc fingers. The most that Ahr is involved in kidney development, and required functionally significant splicing event involves a splice for BaP-induced deficits in nephrogenesis. These results site in exon 9 resulting in the insertion of lysine– indicate that ligand activation of Ahr signaling disrupts threonine–serine between zinc fingers 3 and 4 in the nephrogenesis in vitro, and that this response involves DNA-binding domain (7KTS). These four splice modulation of wt1 alternative splicing and post-transcrip- variants are expressed in the kidney in temporal, spatial, tional control. and evolutionarily stable ratios to support different Oncogene (2003) 22, 2160–2171. doi:10.1038/sj.onc.1206238 functions (Haber et al., 1991; Renshaw et al., 1997; Aswin et al., 1998). In vitro experiments suggest distinct Keywords: Ahr; WT1 splicing; nephrogenesis molecular functions for + and À isoforms. Hetero- zygous mice with a reduction in the +KTS isoform develop glomerulosclerosis, while homozygous mutants of both strains die after birth because of kidney defects. Introduction A second translational initiation site has been identified that gives rise to WT1 proteins of higher molecular Nephrogenesis proceeds through a series of carefully weight (Bruening and Pelletier, 1996; Scharnhorst et al., integrated cell–cell and cell–matrix interactions invol- 1997). The combination of alternative splicing, alter- ving specific induction of metanephric blastema by the native translation start sites, and RNA editing leads to ampullary portion of the ureteric bud and epithelializa- the expression of at least 24 different WT1 isoforms tion (Saxon, 1987). The mechanisms of disrupted (Sharma et al., 1994). nephrogenesis are largely unknown, but interference The essential role of wt1 in kidney development was with genes that encode transcriptional regulatory or unequivocally proven by the phenotype of homozygous wt1 knockout mice which fail to develop metanephric *Correspondence: KS Ramos, Center for Environmental and Rural kidney and die in utero. In homozygous wt1 knockout Health, Texas A&M University, College Station, TX 77843-4455, mice, the ureteric bud fails to grow out of the USA; E-mail: [email protected] mesonephric duct and metanephric mesenchyme dies Received 4 June 2002; revised 8 November 2002; accepted 12 November (Kreidberg et al., 1993). wt1 is mutated in a proportion 2002 of embryonic kidney tumors or nephroblastomas, Role of Ahr signaling in WT1 splicing MH Falahatpisheh and KS Ramos 2161 tumors characterized histologically by incomplete at- Ahr dependent. Other studies have provided evidence tempts at epithelialization. Repression of Pax-2 by wt1 that Ahr participates in the development of prostate, has been demonstrated in vitro (Ryan et al., 1995), a thymus, and ovaries (Hundeiker et al., 1999). A role for response believed to be necessary for renal cell Ahr in renal development was established based on the differentiation. In the mature kidney, expression of observation that exposure of Ahr (+/+) mice to wt1 ultimately becomes confined to the podocyte layer TCDD, an Ahr agonist, induces hydronephrosis, small of the nephron (Pritchard-Jones et al., 1990). The kidneys, tortous ureters, and dilation of the renal pelvis importance of wt1 in kidney development is reflected and ureters (Peters et al., 1999). Hydronephrosis refers by mutations which lead to Denys–Drash syndrome to the dilation of the renal calyces and pelvis proximal to (DDS) and Frasier syndromes (FS). DDS patients a point of obstruction that interrupts the unidirectional exhibit defects in podocyte structure and suffer from flow of urine. However, virtually nothing is known diffuse mesangial sclerosis, urogenital abnormalities, about the pathogenesis of developmental renal disor- and high risk of development of Wilms’ tumors. ders. Glomerular nephropathy is the most consistent finding The molecular mechanisms responsible for deficits in in DDS (Habib et al., 1985). FS patients have focal renal development following inappropriate Ahr signal- segmental glomerular sclerosis attributed to shifts in the ing are unknown. Evidence is presented here that normal +KTS isoform ratio and predominance of unregulated activation of Ahr signaling by BaP inter- ÀKTS isoforms (Barbaux et al., 1997). Developmental feres with glomerulogenesis, branching morphogenesis, regulation of transcription factors by alternative splicing and podocyte differentiation in vitro. These alterations is a widespread phenomenon, with functional implica- correlate with a marked induction of ÀKTS wt1 tions for DNA binding specificities and affinities, transcripts and decreases in WT1 protein levels. activation and repression properties, and protein dimer- ization. Ahr is a member of the large basic helix–loop–helix (bHLH) and PAS homology domain family of tran- Results scription factors that includes proteins involved in myoblast differentiation, such as MyoD, the cellular Induction of metanephric mesenchyme, condensation, response to hypoxia, such as Arnt (Ahr nuclear and subsequent nephron development were monitored translocator) and hypoxia-inducible factor-1 (HIF-1), in metanephric cultures from E11.5 C57BL/6J mice. the Drosophila neurogenic protein Sim (‘single- Murine cultures underwent normal differentiation in the minded’), and the Drosophila circadian rhythm protein presence of vehicle (DMSO), as evidenced by condensa- Per (‘period’). bHLH–PAS proteins generally form tion of renal blastema, formation of comma- and S- heterodimeric transcription factors that regulate devel- shaped bodies, glomerologenesis, and ureteric bud opment and differentiation. Within this family, Ahr is formation (Figures 1–4). Ahr expression was detected the only member conditionally activated in response to in day 4 metanephric cultures by RT–PCR, and Ahr ligand binding. Although an endogenous ligand for Ahr DNA binding was activated by Ahr ligands (data not has not yet been identified, environmental hydrocarbons shown). Treatment with 3 mm BaP, a hydrocarbon ligand and dietary indole carbinols are known to activate Ahr of Ahr, decreased the rates of glomerulogenesis and signaling (Crews and Fan, 1999). Following hydrocar- compromised cellular differentiation within the glomer- bon ligand binding within the PAS domain, the cytosolic ular region (Figure 1a, panels 4–6). The blastema in the Ahr undergoes a conformational change, dissociates proliferating zone appeared less condensed, with deficits from two 90 kDa heat-shock proteins and the hepatitis B in cellular differentiation involving mostly glomerular virus X-associated protein 2 (XAP2) and translocates to mesenchymal cells. Morphometric analysis of BaP- the nucleus where it dimerizes with Arnt (Carver and treated metanephric cultures revealed decreases in Bradfield, 1997). The Ahr/Arnt heterodimer interacts comma- and S-shaped bodies and numbers of glomeruli with Ahr responsive elements (50-TNGCGTG-30) up- and tubulo-epithelial structures (Figure 1b, c, respec- stream of target genes to activate/repress transcription tively), and increases in the number of undifferentiated of target genes. The ligand-activated Ahr regulates glomerular cells (Figure 1d). expression of several drug-metabolizing enzymes (Ne- To further examine the effect of BaP on nephrogen- bert, 1994) and several growth regulatory genes (Zaher esis, whole-mount metanephroi were stained with et al., 1998; Kim et al., 2000). fluorescein-dolichos biflorus (DBA), a lectin specific Ahr has been implicated in several disorders of for the ureteric bud. Ureteric buds developed in both environmental etiology including atherosclerosis, chlor- control and BaP-treated cultures, but significant de- acne, cleft palate, immunosuppression, thymic atrophy, creases in the number of branching points were observed and certain types of malignancies (Zaher et al., 1998; in metanephric cultures treated with the hydrocarbon Kim et al., 2000). Several studies have established a role (Figure 2b). This effect was confined to the second- and for Ahr in environmentally mediated disruption of third-tier branching points of the ureteric bud (Figure 2a, development. For instance, Schmidt et al. (1996) panels 3 and 4). Nephron formation and glomerulogen- demonstrated that Ahr is involved in the regulation of esis were evaluated by labeling whole-mount metane- normal liver growth. Hushka et al. (1998) showed that phroi with rhodamine-coupled peanut agglutinin the development of mammary gland is at least in part (PNA), which stains glomerular podocytes. The number

Oncogene Role of Ahr signaling in WT1 splicing MH Falahatpisheh and KS Ramos 2162

Figure 1 Deficits in glomerulogenesis and mesenchymal-to-epithelial transition in murine metanephros organ cultures challenged with 3 mm benzo(a)pyrene. BaP (3 mm) or an equivalent volume of DMSO was added to the medium daily for 4 days. Kidneys were harvested and fixed in situ for microscopic monitoring as described in Materials and methods. (a) BaP induced deficits of comma- and S-shaped bodies formation (compare panels 1 and 4) and cellular differentiation in the glomerular region. BaP reduced condensation of renal blastema and inhibited glomerulogenesis and tubulogenesis (compare panels 2 and 5). BaP inhibited podocytes differentiation and increased numbers of hyperproliferative phenotypes (arrowheads in panels 3 and 6). (b) Morphometric analysis of control and BaP- treated cultures showed a significant reduction in comma- and S-shaped bodies. Data are presented as mean7s.d. (c) A significant decrease in the number of glomeruli and tubules was observed in organ cultures challenged with BaP (Po0.05). Data are presented as mean of number of cells7s.d. (d) A significant increase in glomerular cellularity was observed in organ cultures challenged with BaP (Po0.05). Data are presented as mean of number of cells7s.d. The magnification was  226 in panels 1 and 4,  289 in panels 2 and 5, and  367 in panels 3 and 6. The results shown are representative of four separate experiments

of glomeruli was markedly reduced in cultures treated Given the essential role of wt1 in nephrogenesis, with BaP for 4 days (Figure 3). Therefore, immuno- experiments were conducted next to evaluate wt1 fluorescence measurements of ureteric bud growth and expression in cultures treated with BaP. Reverse nephron formation validate histological findings and transcriptase (RT)–PCR showed that wt1 mRNA was show that hydrocarbon treatment inhibits nephrogenesis expressed in differentiating cultures of naı¨ ve metaneph- and branching morphogenesis. Monitoring of glomer- ric kidney (Figure 5a). Four major splice variants of wt1 ulogenesis by electron microscopy showed that BaP were detected in developing cultures (Figure 5a). Loca- inhibited podocyte differentiation, development of lization of wt1 mRNA by in situ hybridization revealed podocyte foot processes, and formation of basement that only the cortex expressed wt1, consistent with membranes (Figure 4, panels d–f). These results indicate glomerular expression in S-shaped bodies and podocytes that BaP disrupted nephrogenesis, and preferentially within developing glomeruli (Figure 5b). The effects of inhibited podocyte differentiation and glomerulogenesis BaP on wt1 mRNA were further examined by real-time in metanephric organ cultures. PCR using a primer set that recognizes most major wt1

Oncogene Role of Ahr signaling in WT1 splicing MH Falahatpisheh and KS Ramos 2163

Figure 2 Effects of BaP on ureteric bud growth. Metanephroi cultures were established from 11.5 embryos and challenged with vehicle (DMSO) or 3 mm BaP for 4 days. (a) Ureteric buds were visualized by DBA staining of the whole-mount of organ cultures. (b) Quantitative analysis of branching points. Significant decreases in the number of branching points were observed in metanephroi treated with BaP. Data are presented as the mean of branching points of ureter buds7s.d. *Po0.05 vs control, N ¼ 10 variants. No alterations in total mRNA levels were reports showing that Ahr mediates deficits in craniofa- observed in BaP-treated cultures compared to controls cial, prostate and reproductive development, as well as (Figure 5c). Using primer set P1+P2 to amplify the hydronephrosis (Peterson et al., 1993; Schmidt et al., +KTS form and primer set P1+P3 to amplify the 1996; Hundeiker et al., 1999). To determine if activation ÀKTS form, the expression of the major splice variants of Ahr is involved in the regulation of nephrogenesis in developing kidney was examined. When PCR and WT1 expression, the influence of hydrocarbon reactions were separated by gel electrophoresis, PCR treatment in C57BL/6J Ahr knockout mice compared to products containing the exon 5 alternative splices were wild-type counterparts was evaluated in metanephric discriminated from those that lack this insert on the cultures. Ahr was essential for the spatio-temporal basis of a 51-bp difference in size. BaP treatment regulation of metanephric development, as evidenced increased the expression of + and ÀKTS variants, but by retardation of cellular growth in metanephric the response was most pronounced for the ÀKTS cultures from Ahr À/À mice compared to Ahr +/À isoform (compare Figure 6a, b). Thus, modulation of mice (data not shown). The proposed role for Ahr the ratio of wt1 splice variants may contribute to the signaling in nephrogenesis was consistent with the antidifferentiation effects of the hydrocarbon. finding that further deficits of podocyte differentiation Further experiments were conducted to evaluate WT1 and metanephric development were not observed protein levels in metanephric cultures challenged with in hydrocarbon-treated organ cultures from Ahr null BaP. In control cultures, immunolocalization of WT1 mice (Figure 8). To further evaluate the role of Ahr demonstrated an increased signal in condensing me- signaling in nephrogenesis, the interaction of a-naphtho- senchyme, with expression at different stages of kidney flavone, an Ahr antagonist, with BaP was examined. a- development (Figure 7a). The level of WT1 protein was Naphthoflavone completely abolished disruption of markedly reduced in cultures challenged with BaP nephrogenesis by BaP, suggesting that unregulated (Figure 7a). Quantitative immunocytochemistry showed Ahr signaling mediates wt1 deregulation and disruption a significant decrease (Po0.05) in WT1 immunoreactiv- of nephrogenesis (Figure 9, panels a–f). This finding is ity in glomerular mesenchymal cells challenged with BaP consistent with the inability of BaP to interfere with the (Figure 7b). Western analysis confirmed the reduction of ratio of KTS variants in Ahr knockout mice (data not WT1 protein levels in hydrocarbon-treated cultures shown). (Figure 7c). Together, these data suggest that BaP treatment influences alternative wt1 splicing and post- transcriptional regulation of wt1. Ahr is involved in vascular development, as evidenced Discussion by the disruption of vasculogenesis following unregu- lated activation of Ahr signaling (Lahvis et al., 2000). Its In the embryonic kidney, reciprocal interactions be- role in mammalian development is consistent with tween metanephric mesenchyme and epithelial ureteric

Oncogene Role of Ahr signaling in WT1 splicing MH Falahatpisheh and KS Ramos 2164

Figure 3 Effect of BaP on nephron formation. Metanephroi cultures were established from 11.5 embryos and challenged with vehicle (DMSO) or 3 mm BaP for 4 days. (a) Glomerulo-tubular structures were visualized by PNA staining of whole-mount organ cultures. (b) Quantitative analysis of glomerular number/kidney surface area. Significant decreases in glomerulo-tubular structures were observed in metanephroi treated with BaP. Data were presented as the mean of glomerular number/kidney surface area7s.d. *Po0.05 vs control, N ¼ 10

buds give rise to nephrons and collecting ducts that 1997). TCDD, a related hydrocarbon ligand of the Ahr, continue to mature postnatally (Dressler, 1997). Ne- also disrupts mammalian development and induces phron development involves repeated cycles of mesench- hydronephrosis (Peters et al., 1999). These actions may ymal-to-epithelial transition that give rise to glomeruli be mediated by unregulated activation of Ahr, a and tubular structures, while collecting duct develop- hypothesis supported by the finding that BaP interferes ment involves ureteric bud branching and elongation. with alternative splicing of wt1, a key regulator of Evidence is presented here that unregulated activation of nephrogenesis, and induces deficits in metanephric Ahr signaling in metanephric kidney by BaP disrupts growth and differentiation. Although total wt1 mRNA nephrogenesis in vitro, as reflected by deficits in levels were not affected by hydrocarbon treatment, BaP glomerulogenesis and podocyte differentiation (Figures altered KTS ratios by preferential induction of ÀKTS 1-4). Disruption of nephrogenesis represents a primary isoforms in Ahr-expressing cultures (Figure 6b). The response to hydrocarbon challenge, since deficits in induction of both KTS isoforms by BaP is likely ureteric bud development were restricted to secondary compensated by decreases in other isoforms that and tertiary branching points. The observed deficits in neutralize the overall expression of the wt1 gene. Thus, glomerulogenesis are consistent with reports that BaP treatment changes the relative expression of wt1 vascular injury is the most prominent adverse effect of splice variants that bind DNA with differing sequence Ahr ligands in fish and avian species (Kafafi et al., 1993; specificities and affinities (Larsson et al., 1995). Also of Cantrell et al., 1997). interest is that ÀKTS isoforms of wt1 are found in Treatment of pregnant mice with 10 mm BaP during diffuse domains of transcriptional activity within the organogenesis initiates substantial embryopathy because nucleus, while +KTS isoforms are in discrete regions of defects in anterior neuropore closure, turning, yolk associated with elements of the splicing machinery, such sac diameter, and somite development (Winn and Wells, as U2AF65 (Larsson et al., 1995).

Oncogene Role of Ahr signaling in WT1 splicing MH Falahatpisheh and KS Ramos 2165

Figure 4 Ultrastructural deficits in murine metanephros organ cultures challenged with 3 mm benzo(a)pyrene. Kidneys were harvested and fixed in situ for microscopic monitoring as described in Materials and methods. BaP-treated cultures demonstrated less podocyte differentiation, deficits of podocyte foot processes development, and glomerular basement injury compared to controls. Arrows in panels b and d indicate the glomerular basement membrane. P ¼ podocytes, F ¼ foot process. Panels a, b and c ¼ control; panels d, e and f ¼ BaP. The magnification was  3750, in panels a and d, 7000 in panels b and e, and  10 000 in panels c and f

The splicing of wt1 is regulated in a tissue-specific 5. Hewitt and Saunders (1996) suggested that wt1 (À) manner. In the hemopoietic system, the adult kidney exon 5 isoforms negatively regulate cell growth and cortex and the testis, the most abundant transcripts are survival, while wt1 (+) exon 5 isoforms promote those containing exon 5 +KTS (+/+ and +/À), while cellular differentiation. This notion may be overly in the fetal kidney and adult ovary and uterus, the levels simplistic since wt1 (+) exon 5/ÀKTS (+/À) inhibits of transcript + exon 5 are roughly equivalent. While the cell growth to a greater extent than (+/+) wt1 (Kudoh ratio of (+/À) exon 5 transcripts in adult kidney is et al., 1996). Splicing of exon 5 has no effect on the almost twice that of fetal kidney, the ratio of +/ÀKTS DNA-binding activity, but the DNA-binding affinity of remains the same. In contrast to the KTS splice variants, +KTS is dramatically reduced compared to the ÀKTS little information exists on the functional impact of exon isoform. The insertion of KTS disrupts important

Oncogene Role of Ahr signaling in WT1 splicing MH Falahatpisheh and KS Ramos 2166

Figure 5 wt1 mRNA expression in murine metanephros organ cultures treated with 3 mm BaP. Metanephroi from E11.5 were surgically resected from C57BL/6J and cultured for 4 days. Kidneys were harvested and processed for RT–PCR, nonradioactive in situ hybridization, or real-time RT–PCR as described in Materials and methods. (a) RT–PCR amplification of wt1 transcripts from murine metanephros organ cultures. RT–PCR was performed using primers P1, P2, and P3 to amplify all four major splice variants of wt1 gene. PCR products were separated on 1.2% agarose gel to discriminate between splice variants. The products were separated by gel electrophoresis and visualized by SYBRs staining. (b) Nonradioactive in situ hybridization of wt1 mRNA in E12 embryonic kidney cultured for 4 days with digoxigenin-labeled wt1 cRNA probes, wt1 antisense probes hybridized to blastema, comma, and S-tubular stages (arrowheads). (c) wt1 standard curve by real-time RT–PCR. Cycle number is plotted vs the change in normalized reporter signal. For each reaction, the fluorescence signal of the reporter was divided by the fluorescence signal of the passive reference dye to obtain a ratio defined as the normalized reporter (Rn). Ct represents the fractional cycle number at which a significant increase in Rn above a baseline signal can first be detected. BaP did not alter total wt1 mRNA expression in metanephros cultures. The results shown are representative of two separate experiments

interactions of the linker region with adjacent transcriptional control. The importance of +KTS is zinc fingers, thus lowering the stability of the complex evidenced by the complete absence of podocyte foot (Laity et al., 2000). Thus, Ahr-dependent changes processes in mice with reduced +KTS. Although these in 7KTS by BaP may contribute to deficits in isoforms can substitute for each other to some degree differentiation. with no differences in overall expression of wt1 mRNA Several studies have shown that disturbance of the in +KTS knockout mice, relative expression of the +KTS/ÀKTS ratio results in severe abnormalities in different isoforms is tightly controlled (Hewitt and humans. Proper expression of + and À KTS wt1 is Saunders, 1996). Since the histological features of BaP- critical to the formation of a functional glomerulus treated metanephros are reminiscent of those seen in FS (Hammes et al., 2001), as evidenced in FS patients where patients, induction of ÀKTS wt1 by BaP may be critical mutations in wt1 splicing are associated with induction to the disruption of nephrogenesis. Western analysis of ÀKTS isoforms and defects in glomerular podocyte showed that BaP treatment downregulates total WT1 layer formation. Interestingly, ablation of ÀKTS protein levels (Figure 7c). Given the essential role of variants induces hypodysplastic kidneys. In contrast, WT1 in nephrogenesis, it is concluded that changes in +KTS proteins bind to RNA and participate in post- the ratio of WT1 isoforms coupled to reductions in WT1

Oncogene Role of Ahr signaling in WT1 splicing MH Falahatpisheh and KS Ramos 2167

Figure 6 Analysis of wt1 mRNA splice variants expressed in metanephros cultures challenged with 3 mm BaP. BaP (3 mm)oran equivalent volume of DMSO was added to the medium daily for 4 days. Kidneys were harvested at the end of the hydrocarbon treatment and processed for RT–PCR as described in Materials and methods. RT–PCR was performed using two specific sets of primers, P1+P2 and P1+P3, to amplify +KTS and ÀKTS splice variants, respectively. PCR products were separated on a 1.2% agarose gel by electrophoresis and visualized by ethidium bromide staining (shown in Figure 3a). (a) BaP did not alter the expression of +KTS splice variants. (b) BaP selectively induced ÀKTS splice variants. The signal for b-actin is shown for both control and BaP- treated metanephros. Comparable mRNA levels were analysed in all instances. Similar results were seen in two to four separate experiments

Figure 7 Immunohistochemical analysis of murine metanephric organ cultures challenged with 3 mm BaP. BaP (3 mm) or an equivalent volume of DMSO was added to the medium daily for 4 days. Kidneys were harvested at the end of the hydrocarbon treatment and processed for immunochemical detection of WT1 as described in Materials and methods. (a) E11.5 embryonic kidney cultured for 4 days immunolabeled with anti-WT1 showed intense nuclear labeling in podocytes and parietal epithelial cells (arrows). Reduced WT1 expression was observed following hydrocarbon treatment (arrowheads). (b) Quantitative immunocytochemical analysis of WT1 protein expression in murine metanephros. * denotes a significant decrease in WT1 protein expression in E11.5 embryonic kidneys challenged with 3 mm BaP for 4 days compared to controls (Po0.05). (d) Immunoblot Western analysis of murine metanephros probed with WT1 antibody. BaP decreased the level of the most abundant WT1 isoform (52 kDa), but induced a WT1 isoform of 60 kDa. Similar results were seen in four separate experiments

Oncogene Role of Ahr signaling in WT1 splicing MH Falahatpisheh and KS Ramos 2168

Figure 8 Kidney phenotype of murine metanephric organ cultures of Ahr knockout mice challenged with 3 mm benzo(a)pyrene. E11.5 embryonic kidney from Ahr À/À mice were cultured for 4 days. BaP (3 mm) or an equivalent volume of DMSO was added to the medium daily for 4 days. Kidneys were harvested and fixed in situ for microscopic monitoring as described in Materials and methods. Although both control and treated cultures showed retardation of kidney development, no further deficits in nephrogenesis were noted in hydrocarbon-treated AhrÀ/À mice

Figure 9 a-Naphthoflavone (1 mm) inhibits deficits in nephrogenesis induced by 3 mm benzo(a)pyrene. Cultures were pretreated with the inhibitor 2 h before challenge with BaP (3 mm) or an equivalent volume of DMSO daily for 4 days. The inhibitor was maintained throughout the culture period. Kidneys were harvested and fixed in situ for microscopic monitoring as described in Materials and methods. a-Naphthoflavone (1 mm) abolished the inhibition of kidney development induced by BaP, suggesting that Ahr activation mediates BaP-induced deficits in nephrogenesis. The magnification was  367 in panels a, c and e and  400 in panels b, d and f

protein levels mediate deficits in metanephric differen- wt1 splicing and nephrogenesis. Although this hypoth- tiation following Ahr activation. esis awaits further testing, the findings presented here The modulation of wt1 splicing by BaP may suggest a novel function for Ahr ligands as modulators significantly contribute to the disruption of renal of post-transcriptional events during nephrogenesis. development, podocyte differentiation, and glomerular Ahr mRNA and protein are detectable in kidney at mesenchymal proliferation following unregulated acti- GD 10–16, a period of rapid proliferation and vation of Ahr by BaP. Ahr may interfere at multiple differentiation (Abbott, 1995). Ahr plays a role in levels of post-transcriptional control to induce deficits in nephrogenesis, as evidenced by the finding that Ahr null

Oncogene Role of Ahr signaling in WT1 splicing MH Falahatpisheh and KS Ramos 2169 mice exhibited retardation of kidney development (data NIH-Image v1.60 freeware (developed at the National In- not shown), suggesting that Ahr signaling either by stitutes of Health and available via the internet at ftp:// endogenous ligands, or in a ligand-independent manner, zippy.nimh.nih.gov/pub/nih-image). A total of 12 histological participates in kidney development. A role for Ahr in sections each from control and BaP-treated cultures were nephrogenesis is consistent with the finding that examined. The high quality of the sections used allowed for unregulated activation of Ahr signaling by BaP direct visualization and quantification of glomerulo-tubular structures throughout the entire length of the section. mediated deficits of renal differentiation and glomer- Glomerular cellularity was quantified in at least 30 glomeruli ulogenesis. This interpretation is consistent with the from each group, as described by Toth and Tadebayashi (1996). inability of BaP to further compromise nephrogenesis in Ahr null mice (Figure 8), and the protection afforded by Evaluation of branching morphogenesis and nephron formation a-naphthoflavone, an Ahr antagonist (Figure 9). Given that a-naphthoflavone inhibits renal cytochrome P450 Ureteric buds and nephrons were visualized after labeling metabolism of BaP to intermediates that covalently whole-mounted metanephroi with fluorescein DBA and modify DNA and induce oxidative stress (Bowes et al., rhodamine-coupled PNA (Vectro Laboratories, Burlingame CA, USA), respectively, as described by Hida et al. (2002). 1996), a contribution by P450 enzymes to the disruption of nephrogenesis also needs to be considered. Collectively, these data support the hypothesis that Transmission electron microscopy (TEM) deregulation of Ahr signaling by BaP mediates altera- Metanephric kidneys were cut into small pieces with a razor tions in wt1 splicing and disruption of nephrogenesis. blade, fixed with 2.5% glutaraldehyde (0.067 m phosphate The role of Ahr as a mediator of the BaP nephrogenic buffer), dehydrated with an ethanol series, embedded in Epon response may be dependent upon protein–protein and/ 812, and sectioned using an ultramicrotome. Ultrathin sections or protein–DNA interactions that influence wt1 func- were double-stained with uranyl acetate and lead citrate, and inspected by TEM. tion, and/or Ahr-mediated bioactivation of the parent hydrocarbon. RNA isolation Total RNA was extracted from the cells using Tri reagent Materials and methods (Molecular Research Center, Inc., Cincinnati, OH, USA) according to the manufacturer’s specifications. Organ cultures RT–PCR A modification of the whole kidney organ culture system previously described by Avner and co-workers was employed RT–PCR for WT1 was performed as described by Walker et (Avner and Sweeney, 1990). Day 11.5 mouse embryos were al. (1994). Primers used to detect specific KTS splices were: P1, surgically resected from C57bL/6J wild-type or Ahr knockout 50-ATGAGGATCCCATGGGCCAGCA-30; P2, 50-AAGGG- mice and placed in Hank’s balanced salt solution. Embryonic CTTTTCACTTGTTTTAC-30; P3, 50-AAGGGCTTTTCA- kidneys (approximately 0.5 mm  1 mm) were isolated by CCTGTATGAG-30. The reverse transcription reaction was microsurgical dissection and deposited on cell culture inserts. carried out at 941C for 1 min, 50–601C for 1 min, and 721C for The use of a 0.45-mm polyethylene trephalate cyclopore 1 min for 30–35 cycles, and after the cycle the reaction was membrane allowed direct visualization of tissue structure by incubated at 721C for 5 min. phase contrast microscopy. A 25-mm diameter cyclopore insert allowed placement of a minimum of six kidneys in a Nonradioactive in situ hybridization circular pattern. Kidneys were maintained at the liquid–gas interface in the presence of medium consisting of a 1 : 1 mixture Paraffin-embedded sections were dewaxed in xylene, rinsed of Dulbecco’s modified Eagle’s medium (DMEM) and F12 twice in 100% ethanol for 10 min each, and air-dried. Tissues supplemented with 10% fetal bovine serum (FBS) and a 5  were rehydrated through a series of graded ethanol solutions, concentration of MITO serum extender (Becton Dickenson, rinsed three times in ice-cold PBS containing 0.1% Tween 20 Bedford, MA, USA), a source of kidney-relevant hormones (PBT), washed in PBT for 30 min at 41C, brought in PBT to and growth factors. room temperature, and treated with 50 mg proteinase K/ml in PBT at room temperature for 4 min. Sections were fixed in 4% formaldehyde for 10 min followed by washing in PBT three Hydrocarbon treatment times and dehydration through graded ethanol. BaP was added to the medium at 3 mm daily for 4 days. An Probe preparation. Mouse 1170-bp WT1 cDNA (nt 750– equivalent volume of DMSO was used as control. This 1170) was kindly provided by Dr Bryan Williams (Cleveland concentration was chosen based on concentration range- Clinic, Cleveland, OH, USA). WT1 cDNA was prepared as finding studies detailed previously (Bowes and Ramos, 1994). cRNA sense and antisense probes and synthesized with the On day 4, kidneys were harvested and fixed in situ for further uridine 50-triphosphate digoxigenin (DIG-UTP) labeling pro- examination. tocol (Boehringer Mannheim, IN, USA). Full-length cRNA probes were reduced in size to approximately 150 bp by alkaline hydrolysis with 0.2 m carbonate buffer, pH 10.2, and Morphometric analysis verified with agarose gel electrophoresis. H&E slides (5 mm sections) were examined by brightfield light Probe hybridization and detection. The procedure for RNA– microscopy. Computer-assisted morphometric analysis of RNA in situ hybridization using DIG-labeled probes was glomeruli was performed at the Image Acquisition and adopted from methods previously developed by Boehringer Morphometric Analysis Facility of the Center for Environ- Mannheim and sections examined under brightfield micro- mental and Rural Health. Images were captured using the scopy.

Oncogene Role of Ahr signaling in WT1 splicing MH Falahatpisheh and KS Ramos 2170 Real-time PCR was quantified using a computerized image analysis system as described by Gutierrez et al. (1997). Sections from control and The double-stranded DNA-binding dye method was used to BaP-treated cultures were processed together under identical measure RNA levels. WT1 gene primers were chosen using conditions and using the same batch of reagents. For Oligo 4.0 (National Biosciences, Plymouth, MN, USA) and quantitative immunocytochemistry, a standard optical density designed to amplify all major variants of the gene. Reverse (OD) calibration curve was generated from 11 preset neutral transcription of RNA was carried out in a final volume of 20 ml density filters in 0.1 OD steps from 0 to 1.0 (Stouffer Graphics containing IX RT–PCR buffer, 1 mm each of deoxynucleotide Arts equipment, South Bend, IN, USA). The experimental OD triphosphates, 5 mm MgCl ,1U/ml RNase inhibitor, 2.5 U/ml 2 of 20 glomeruli from control and BaP-treated cultures values RT, 50 U oligo d(T), and 200 mg of total RNA. Samples were were in the linear portion of the calibration curve. The values incubated at room temperature for 10 min and 421C for were corrected by subtracting the corresponding background 30 min, and inactivated with heating at 991C for 5 min and in the parenchyma and normalized by glomerular tuff area. cooling at 51C for 5 min. Real-time PCR amplification was The ODs of each group were averaged and the means for BaP- performed using an ABI Prism 7700 Sequence Detection treated cultures compared to control cultures. Statistical System (Perkin–Elmer Applied Biosystems). For each run, analyses data were performed using the Student’s t-test 25 ml of 2X SYBR Master mix (Perkin–Elmer Applied (a ¼ 0.05). Biosystems) and 0.4 mm of both forward and reverse primer along with 10 ml each of appropriate transcriptase samples were mixed. The thermal cycling conditions comprised an Protein harvesting initial denaturation step at 951C for 10 min, 50 cycles at 951C Cultured metanephros were washed with PBS and crushed for 15 s, and 651C for 1 min. All experiments were performed with a needle, adding 50 ml HEGD+PMSF. Next, KC1 in duplicate. (0.5 m) and Triton X-100 (0.01%) were added and samples were incubated on ice for 1 h. Tubes were centrifuged at Immunolocalization of WT1 14000 r.p.m. for 10 min and the supernatant was transferred to fresh tubes. Protein concentration was measured by the A peroxidase-based detection system and secondary reagent method of Bradford (1976). system were used to localize WT1 protein in sections of metanephros organ cultures as described by Yeger et al. (1996). Western analysis Protein samples were boiled for 2 min and applied to 10% Image capture and quantification SDS–PAGE gels. After electrophoresis, proteins were trans- ferred to PDVF membranes and filters probed with a WT1 Immunocytochemistry was quantified by densitometry with a polyclonal antibody (WT (180): sc-846, Santa Cruz Biotech- computer-based image analysis system. Images were captured nology, CA, USA), which recognizes Wilms’ tumor nuclear with the NIH-Image v1.60 freeware (developed at the National protein. Signals were visualized with horseradish peroxidase- Institutes of Health and available via the internet at ftp:// conjugated secondary antibody. zippy.nimh.nih.gov/pub/nih-image). The video signals were converted into a gray-scale digital image consisting of a 640 Â 480 grid of pixels. The brightness level of each pixel ranged from 0 to 225 gray levels. To capture the image, one Acknowledgments glomerulus in the metanephros section was selected and the We thank Drs Robert C Burghardt and Rola Barhoumi for point of focus was moved off the tissue without changing any assistance with electron microscopy and image analysis, and setting and the blank field was captured. Selected sections were Mr Marc Holderman for assistance with Western blot analysis. moved back into view and the same image was captured for 20 Also, we thank Dr Bhagavatula Moorthy for facilitating the glomeruli. The software automatically subtracted the blank acquisition of C57BL/6J Ahr null mice and Dr Cheryl Walker field from the averaged images and corrected images were for valuable comments. This study was supported by NIEHS saved as TIFF files. The intensity of the tissue immunoreaction Grants ES04917 and ES09106.

References

Abbott BD. (1995). Toxicology, 105, 365–373. Bruening W and Pelletier J. (1996). J. Biol. Chem., 271, Aswin M, Lasley M, Micholas DH and Andreas S. (1998). 8646–8654. Kidney Int., 53, 1512–1518. Cantrell SM, Joy-Schlezinger J, Stegeman JJ, Tillitt DE and Avner ED. (1993). Sem. Nephrol., 13, 427–435. Hannink M. (1997). Toxicol. Appl. Pharmacol., 148, 24–34. Avner ED and Sweeney WE. (1990). Pediatr. Nephrol., 4, Carver LA and Bradfield CA. (1997). J. Biol. Chem., 272, 372–377. 11452–11456. Barbaux S, Niaudet P, Gubler MC, Grunfeld JP, Jaubert F, Crews ST and Fan CM. (1999). Curr. Opion. Gen. Dev., 9, Kuttern F, Fekete CN, Souleyreau-Theville N, Thibaud E, 580–587. Fellous M and McElreavey K. (1997). Nat. Genet., 17, Dressler GR. (1997). Adv. Nephrol. Necker Hosp., 26, 1–17. 467–470. Drumond IA, Madden SL, Rohwer NP, Bell GI, Suklhatme Bowes RC, Parrish AR, Steinberg MA, Willet KL, Zhao W, VP and Rauscher FI. (1992). Science, 257, 674–678. Savas U, Jefcoate CR, Safe SH and Ramos KS (1996). Gessler M, Konig A and Bruns GA. (1992). Genomics, 12, Biochem. Pharmacol., 52, 587–595. 807–813. Bowes RC and Ramos KS (1994). Toxicol. In Vitro, 8, Gutierrez A, Khan ZU, Miralles CP, Mehta AK, Ruano D, 1151–1160. Araujo F, Victorica J and De Blas AL. (1997). Mol. Brain Bradford MM. (1976). Anal. Biochem., 72, 248–254. Res., 45, 59–70.

Oncogene Role of Ahr signaling in WT1 splicing MH Falahatpisheh and KS Ramos 2171 Haber DA, Sohn RL, Bucker AJ, Pelletier J, Call KM and Peters JM, Narotsky MG, Elizondo G, Fernandez-Salguero Housman DE. (1991). Proc. Natl. Acad. Sci. USA, 88, PM, Gonzalez FJ and Abbott BD. (1999). Toxicol. Sci., 47, 9618–9622. 86–92. Habib R, Loirat C, Gubler MC, Niaudet P, Bensam A, Levy Peterson RE, Theobald HM and Kimmel GL. (1993). Crit. M and Broyer M. (1985). Clin. Nephrol., 24, 269–278. Rev. Toxicol., 23, 283–337. Hammes A, Guo JK, Lutsch G, Leheste JR, Landrock D, Pritchard-Jones K, Flering S, Davidson D, Bickmore W, Siegler U, Gubler MC and Schedl A. (2001). Cell, 106, Porteus D, Gosden C, Bard J, Buckler A, Pelletier J and 319–329. Housman D. (1990). Nature, 346, 194–197. Hewitt SM and Saunders GF. (1996). Anticancer Res., 16, Renshaw J, King-Underwood L and Pritchard-Jones K. 621–626. (1997). Genes Chrom. Cancer, 19, 256–266. Hida M, Omori S and Awazu M. (2002). Kidney Int., 61, Ryan G, Steelepperkins V, Morris JF, Rauscher FJ and 1252–1262. Dressler GR. (1995). Development, 121, 867–875. Hundeiker C, Pineau T, Gassar G, Betensky RA, Gleichmann Saxon L. (ed). (1987). Organogenesis of the Kidney. Cambridge E and Esser C. (1999). Int. J. Immunopharmacol., 21, University Press: Cambridge, UK. 841–859. Scharnhorst V, Deker P, Vander-EB AJ and Jochemsen AG. Hushka LJ, Williams JS and Greenlee WF. (1998). Toxicol. (1999). J. Biol. Chem., 274, 23456–23462. Appl. Pharmacol., 152, 200–210. Scharnhorst V, Kranenburg O, Van Der EB AJ and Kafafi SA, Afeefy HY, Said HK and Kafafi AG. (1993). Chem. Jochemsen AG. (1997). Cell Growth Differ., 8, 133–143. Res. Toxicol., 6, 328–334. Schmidt JV, Huei-Ting Su GH, Reddy JK, Simon MC and Kim DW, Gazourian L, Quadri SA, Romieu-Mourez R, Bradfield CA. (1996). Proc. Natl. Acad. Sci. USA, 93, Sherr DH and Sonenshein GE. (2000). Oncogene, 19, 6731–6736. 5498–5506. Sharma PM, Bowman M, Madden SL, Rauscher FJ and Kreidberg JA, Sariola H, Loring JM, Maeda M, Pelletier J, Sukumar S. (1994). Genes Dev., 8, 720–731. Housman D and Jaenisch R. (1993). Cell, 74, 679–691. Toth T and Takebayashi S. (1996). Nephron, 74, 64–71. Kudoh T, Ishidate T, Nakamura T, Toyoshima K and Walker C, Rutten F, Yuan X, Pass H, Mew DM and Everitt J. Akiyama T. (1996). Oncogene, 13, 1431–1439. (1994). Cancer Res., 54, 3101–3106. Lahvis GP, Lindell SL, Thomas RS, McCluskey RS, Murphy Wang ZY, Masdden SL, Deuel TF and Rauscher FI. (1992). J. C, Glover E, Bentz M, Southard J and Bradfield CA. (2000). Biol. Chem., 267, 21999–22002. Proc. Natl. Acad. Sci. USA, 97, 10442–10447. Winn LM and Wells PG. (1997). Free Rod. Biol. Med., 22, Laity JH, Chung J, Dyson J and Wright PE. (2000). 607–621. Biochemistry, 39, 5341–5348. Yeger H, Forget D, Alami J and Williams B. (1996). In Vitro Larsson SH, Charlieu JP, Miyagawa K, Engelkamp D, Cell Dev. Biol., 32, 496–504. Rassoulzadegan M, Ross A, Cuzin F, Heyningen V and Zaher H, Fernandez-Salguero PM, Letterio J, Sheikh MS, Hastie ND. (1995). Cell, 81, 391–401. Fornace AJ, Roberts AB and Gonzalez FJ. (1998). Mol. Nebert DW. (1994). Biochem. Pharmacol. 47, 25–37. Pharmacol., 54, 313–321.

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