Differential Expression of S6K2 Dictates Tissue-Specific Requirement for S6K1 in Mediating Aberrant Mtorc1 Signaling and Tumorigenesis

Published OnlineFirst March 28, 2011; DOI: 10.1158/0008-5472.CAN-10-3962

Cancer Therapeutics, Targets, and Chemical Biology Research

Differential Expression of S6K2 Dictates Tissue-Specific Requirement for S6K1 in Mediating Aberrant mTORC1 Signaling and Tumorigenesis

Caterina Nardella1, Andrea Lunardi1, Giuseppe Fedele2, John G. Clohessy1, Andrea Alimonti1, Sara C. Kozma5, George Thomas5, Massimo Loda2–4,6, and Pier Paolo Pandolfi1

Abstract The S6K1 and S6K2 kinases are considered important mTOR signaling effectors, yet their contribution to tumorigenesis remains unclear. Aberrant mTOR activation is a frequent event in cancer that commonly results from heterozygous loss of PTEN. Here, we show for the first time a differential protein expression between S6K1 and S6K2 in both mouse and human tissues. Additionally, the inactivation of S6k1 in the context of Pten þ heterozygosity (Pten / ) suggests a differential requirement for this protein across multiple tissues. This tissue specificity appears to be governed by the relative protein expression of S6k2. Accordingly, we find that deletion of þ S6k1 markedly impairs Pten / mediated adrenal tumorigenesis, specifically due to low expression of S6k2. Concomitant observation of low S6K2 levels in the human adrenal gland supports the development of S6K1 inhibitors for treatment of PTEN loss–driven pheochromocytoma. Cancer Res; 71(10); 1–7. 2011 AACR.

Introduction splenomegaly (4) and are extremely susceptible to develop- ing a wide spectrum of epithelial tumors (5). Aberrant activation of the phosphatidylinositol-3 kinase Downstream of the PI3K/PTEN pathway, the mTOR complex (PI3K) pathway plays a key role in tumorigenesis through 1 (mTORC1) has been shown to be an essential effector regulation of pivotal biological processes including prolif- in promoting cell proliferation and susceptibility to cancer eration, growth, survival, and migration (1). A major reg- development (reviewed in ref. 6). mTORC1 becomes highly ulator of this pathway is the tumor suppressor phosphatase active in the absence of PTEN and promotes cell growth through and tensin homolog deleted on chromosome 10 (PTEN) phosphorylation of important regulators of protein translation gene. PTEN negatively regulates the PI3K signaling cascade including the well-characterized ribosomal protein S6 kinase and is now established as one of the most frequently (S6K) and the eukaryotic translation initiation factor 4E binding mutated, deleted, and silenced tumor suppressor genes in protein 1 (4EBP1; reviewed in ref. 7). These 2 mTORC1 sub- human cancer (2). We have previously established several strates represent 2 distinct signaling pathways downstream of faithful mouse models to elucidate the role of Pten in cancer mTORC1. Phosphorylation of 4EBP1 leads to its uncoupling (reviewed in ref. 3). Mice engineered to have only one allele from the eukaryotic initiation factor 4E (eIF4E), whereas activa- þ of Pten (Pten / mice) die prematurely as a result of an tion of the S6K protein family results in the phosphorylation of autoimmune disorder characterized by massive lympho- additional downstream targets including the 40S ribosomal protein S6 (RpS6; ref. 8), eIF4B (9), eEF2 kinase (10), and the tumor suppressor PDCD4 (11). Release of eIF4E from 4EBP1 and the phosphorylation of RpS6 result in the upregulation and Authors' Affiliations: 1Cancer Genetics Program, Beth Israel Deaconess activation of the translation machinery (7). Cancer Center, Departments of Medicine and Pathology, Beth Israel Deacon- ess Medical Center, Harvard Medical School; 2Department of Medical Downstream of mTOR, the role of the 4EBP1/eIF4E branch Oncology, Dana-Farber Cancer Institute; 3Departmentof Pathology, Brigham of the pathway in tumorigenesis has been extensively studied 4 and Women's Hospital, Harvard Medical School; Center for Molecular both in vivo and in vitro (12, 13; and reviewed in ref. 14). OncologicPathology, Dana-Farber Cancer Institute,Boston,Massachusetts; 5Department of Cancer and Cell Biology, Metabolic Diseases Institute, Uni- In contrast, the contribution of the S6K arm of the mTOR versity of Cincinnati, Cincinnati, Ohio; and 6Broad Institute of Harvard and signaling cascade in oncogenesis has been less well investi- Massachusetts Institute of Technology, Cambridge, Massachusetts gated. The S6K family consists of 2 kinases, S6K1 and S6K2 Note: Supplementary data for this article are available at Cancer Research (15–18). To date, both kinases are reported to be ubiquitously Online (http://cancerres.aacrjournals.org/). expressed, with mRNA expression detected in all mouse and Corresponding Author: Pier Paolo Pandolfi, Beth Israel Deaconess Med- – ical Center, Harvard Medical School, 330 Brookline Avenue, Boston, MA human tissues examined (15 17). In addition, knockout mice 02115. Phone: 617-735-2141; Fax: 617-735-2120; for S6k1 or S6k2 alone show that there is redundancy between E-mail: [email protected] both genes, and it has also been suggested that inactivation of doi: 10.1158/0008-5472.CAN-10-3962 one may be compensated for through upregulation of the 2011 American Association for Cancer Research. other (15, 19). This has made it difficult to properly understand

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the role of the S6K signaling arm in cancer. However, over- Human sample analysis expression of both S6K1 and S6K2 have been reported in Human tissue lysates (Leinco Technologies) were probed breast cancer (20), whereas a recent report showed that only with S6K1 (Cell Signaling Technology; 49D7 Rabbit S6k1 is required for insulinoma formation induced by expres- mAb); S6K2 (Bethyl Laboratories); and GAPDH (14C10 Cell sion of constitutively active Akt1 in the mouse pancreas (21). Signaling Technology). Human sections were analyzed by Thus, the tissue-specific requirement of both S6K1 and S6K2 immunohistochemistry (IHC) with S6K2 antibody (Bethyl in oncogenesis remains an open question, and one that is very Laboratories). relevant for the therapeutic targeting of this arm of the Original H&E sections from 16 postdiagnostic cases of pathway. human pheochromocytoma were reviewed to verify the his- Here we show that S6k1 genetic deletion can suppress tologic diagnosis. S6K1 immunostaining (Cell Signaling Tech- phenotypes mediated by Pten haploinsufficiency in an exqui- nology; 49D7 Rabbit mAb) was evaluated independently by 2 site tissue-specific fashion. This tissue specificity appears to be pathologists (M. Loda and G. Fedele) and scored as negative dictated by the abundance of S6K2 protein levels. Indeed, we (0), weak (1), moderate (2), or strong (3). All human sections report for the first time that, in contrast to S6K1, S6K2 protein were collected following Institutional Review Board approval levels vary profoundly among different tissues. at the Brigham and Women's Hospital.

Materials and Methods Phylogenetic analysis Multiple alignments of amino acid sequences were carried S6k1 and Pten mice out with ClustalW (23). Amino acid sequences for human þ S6k1 / and Pten / mice were previously generated (15, (Homo sapiens): RPS6Kb1 (NP_003152.1), RPS6Kb2 22) and were crossed through several generations of breeding (NP_003943.2); cow (Bos taurus): RPS6Kb1 (NP_991385.1), to ensure normalization of the background strains. All mouse RPS6Kb2 (XP_582478.4); rat (Rattus norvegicus): RPS6Kb1 work was carried out in accordance with our Institutional (NP_114191.1), RPS6Kb2 (NP_001010962); mouse (Mus mus- Animal Care and Use Committee approved protocol. For culus): RPS6Kb1 (NP_001107806), RPS6Kb2 (NP_067460.1); genotyping, tail DNA was subjected to PCR following the rabbit (Oryctolagus cuniculus): RPS6Kb1 (NP_001095160); protocols previously described (15; 22). chicken (Gallus gallus): RPS6K (NP_001025892.1); zebrafish (Danio rerio): RPS6K (NP_998241.1); frog (Xenopus laevis): Histopathology and immunohistochemistry RPS6Kb-1 (NP_001080935). Mice were autopsied, and tissues were extracted and fixed in 10% neutral-buffered formalin (Sigma) overnight, subse- Results quently washed once with PBS, transferred into 50% ethanol, and stored in 70% ethanol. After that, the tissues were S6k1 deletion impacts Pten heterozygous–driven embedded in paraffin, sectioned, and stained with hematox- phenotypes in a tissue-specific manner ylin and eosin (H&E) in accordance with standard procedures. To explore the contribution of the S6K1 arm of mTORC1 Sections were stained with the following antibodies: B220 (BD signaling to the phenotype dictated by Pten heterozygosity, we þ Pharmingen); CD3 (Dako); synaptophysin (Dako); phospho-S6 crossed Pten / mice with Rps6kb1-null (S6k1 / ) mice. In (S235/S236; Cell Signaling Technology); Ki-67 (Novacastra); particular, we have focused on 4 specific genotypes for our þ þ and S6K1 (Cell Signaling Technology; 49D7 Rabbit mAb). study: wild type (wt), S6k1 / , Pten / , and S6k1 / ;Pten / mice. Initially, these cohorts were evaluated for long-term Quantitative real-time PCR survival. Surprisingly, genetic deletion of S6k1 had no effect on þ Total RNA was prepared from mouse tissues using the the lifespan of Pten / mice (Fig. 1A). We have previously þ Trizol method (Invitrogen). cDNA was obtained with reported that Pten / mice die from an autoimmune disorder, iScriptTM cDNA Synthesis Kit (Bio-Rad). Taqman probes were characterized by a severe lymphadenopathy affecting mainly obtained from Applied Biosystems. Amplifications were run in the submandibular, axillary, and inguinal lymph nodes (4). þ a 7900 Real-Time PCR System (Applied Biosystems). Each Thus, we examined the S6k1 / ;Pten / mice to determine value was adjusted by using Hprt1 levels as reference. whether this was also the case for this population of mice. þ þ Indeed, the lymph nodes from Pten / and S6k1 / ;Pten / Western blot analysis on murine tissues mice were found to be indistinguishable in composition, with Cell lysates were prepared with RIPA buffer [1 PBS, 1% lymph nodes from both genotypes exhibiting an expansion Nonidet P40, 0.5% sodium deoxycholate, 0.1% SDS, and pro- of B- and T-lymphocytes as characterized by IHC with the tease inhibitor cocktail (Roche)] and cleaned by centrifuga- B-lymphocyte–specific marker B220 and the T-lymphocyte tion. The following antibodies were used for Western blot marker CD3 (Fig. 1B). Furthermore, lymph nodes from þ þ analysis: glyceraldehyde 3 phosphate dehydrogenase (GAPDH; Pten / and S6k1 / ;Pten / mice showed no significant 14C10 Cell Signaling Technology); S6K1 (Cell Signaling Tech- differences in positive staining for the cell proliferation marker nology; 49D7 Rabbit mAb); S6K2 [p70 S6 kinase b (C-19) Santa Ki-67 (Fig. 1C, top). Thus, these data suggest that S6k1 deletion Cruz Biotechnology]; phospho-S6 (S235/S236; Cell Signaling does not impact the increased lymph node proliferation Technology); total S6 (Cell Signaling Technology); and Pten triggered by Pten heterozygous loss. Additionally, staining þ (Cell Signaling Technology). of S6k1 / ;Pten / lymph nodes for phosphorylation of the

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A B 100

80 Wt (n = 24) Pten+/– Double S6k1–/– (n = 24) S6k1 60 Figure 1. Impact of genetic Pten+/– (n= 23) deletion on lymph node 40 Double (n = 22) proliferation and 20 pheochromocytoma formation survival Percentage ×10 ×10 triggered by heterozygous loss of 0 Pten. A, Kaplan–Meier plot for 0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 Pten+/– Double overall survival shows no Months difference between S61k/; C Pten+/– 30.7% ± 5.7% Double 29.3% ± 5.8% Ptenþ/ (double) and Ptenþ/ mice. B, sections of lymph B220 nodes from 12-month-old × × Ki-67 20 20 S6k1/;Ptenþ/ and Ptenþ/ × × mice stained with H&E (top); 40 40 Pten+/– Double anti-B220, a specific marker of B- Pten+/– 28.9% ± 5.5% Double 21.9% ± 4.6% lymphocytes (middle); anti-CD3, a specific marker of T-lymphocytes (bottom). C, sections of lymph CD3 H&E p-S6 nodes from 12-month-old ×20 ×20 / þ/ þ/ S6k1 ;Pten and Pten ×40 ×40 mice stained with Ki-67 (top); anti-phospho-S6 (bottom). H&E Synaptophysin Quantifications of Ki-67 and DEWt Pten+/– wt –/– phospho-S6 positive cells are wt S6k1 Double n = 14 indicated. D, sections of adrenal 100 n = 12 wt glands from 10-month-old , 80 S6k1/, Ptenþ/, and S6k1/; þ/ 60 Pten mice stained with: H&E ×10 ×10 n = 10 (left) and anti-synaptophysin, a 40 S6k1–/– S6k1–/– n =1 0 specific marker of the medulla of 20 the adrenal gland (right). E, n = 10 % pheocromocytoma n = 10 n = 9 n = 9 cumulative incidence of adrenal glands positive 0 8–12 months 13–16 months pheochromocytoma over time in þ wt, S6k1 / , S6k1 / ;Pten / , ×10 ×10 þ/ F and Pten mice. F, sections of +/– ± ± +/– Pten+/– Pten 12.4% 2.7% Double 2.6% 0.8% adrenal gland from 10-month-old Pten S6k1/;Ptenþ/ and Ptenþ/

mice stained with Ki-67 (top); Ki-67 anti-phospho-S6 (bottom). Quantifications of Ki-67 and ×10 ×10 ×40 ×40 phospho-S6 positive cells are Pten+/– 6.5% ± 3.04% Double 0.7% ± 0.2% indicated. Double Double p-S6

×40 ×40 ×10 ×10

þ S6K1 downstream target RpS6 (phospho-S6) showed only a To further characterize the S6k1 / ;Pten / mice we slight reduction in phosphorylation as compared with lymph examined the impact of S6k1 geneticdeletionintumorigen- þ þ nodes from Pten / mice (Fig. 1C, bottom). This observation esis driven by Pten heterozygous loss. Pten / mice are was further confirmed by Western blot analysis and its highly prone to develop spontaneous epithelial tumors in quantification (Supplementary Fig. S1A). a variety of tissues (5). However, some of the tumors driven Taken together, our data suggest that S6k1 deletion has by Pten heterozygosity occur after a long latency and at little impact on the proliferative advantage conferred by Pten incomplete penetrance. Thus, we focused on pheochromo- heterozygous loss, consistent with the comparable survival cytoma as it is the most penetrant phenotype at earlier time þ þ rates between Pten / and S6k1 / ;Pten / cohorts of mice. points in our genetic background (5). As we have previously þ Furthermore, the modest decrease in phospho-S6 staining and reported, Pten / mice develop a marked expansion and equivalent proliferation in the lymph nodes suggests redun- proliferation of chromaffin cells in the medulla of the dancy between S6k1 and S6k2, as previously reported for the adrenal gland. This expansion is typical of pheochromocy- þ S6k1-deficient mice (15). toma, with 100% of Pten / mice showing this phenotype by

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þ þ 9 months of age (5). Strikingly, the S6k1 / ;Pten / mice 100% in Pten / ;Fig.1E).Wealsoidentifiedaprofound showed a dramatic reduction in the proliferation of the suppression of proliferation as characterized by Ki-67 stain- þ þ chromaffin cells as compared with Pten / mice (Fig. 1D, ing in the adrenal medullas of the S6k1 / ;Pten / versus þ left). This is confirmed by staining the adrenal glands with those of the Pten / mice (Fig. 1F, top). In addition, deletion þ both synaptophysin and chromogranin A, specific markers of S6k1 in the Pten / background resulted in a notable of the adrenal medulla (Fig. 1D, right and Supplementary reduction in phoshpo-S6 in these adrenal glands (Fig. 1F, Fig. S1B, respectively). Pathologic analysis of the S6k1 / ; bottom and Fig. 2C), highlighting the relevance of the S6k1 þ Pten / mice at 8 to 12 months of age revealed a 20% arm of mTORC1 signaling in driving proliferation triggered incidence of pheochromocytoma when compared with com- by Pten heterozygous loss in this tissue. Thus, the marked þ þ plete penetrance in age-matched Pten / mice(Fig.1E).At impairment in Pten / driven pheochromocytoma indicates þ 13 to 15 months of age the S6k1 / ;Pten / still showed a a lack of redundancy between S6k1 an S6k2 in this tissue and, markedly lower penetrance of the tumor phenotype com- in conjunction with the contrasting results obtained in the þ þ pared with Pten / mice (40% in S6k1 / ;Pten / versus lymph nodes, clearly shows that the genetic deletion of S6k1

A 4.5

4 S6K1 3.5 S6K2 3

2.5

DDCt 2

1.5

0.5

0 Lymph node Adrenal Uterus Heart Kidney B gland

S6k1 Figure 2. S6K1 and S6K2 proteins are differentially expressed in S6k2 * mouse tissues. A, TaqMan RT- PCR analysis of the RNA from a Pten panel of tissues from wt mice with S6k1- and S6k2-specific probes. P-S6 Error bars show SD from 3 independent experiments. B, Western blot analysis from the S6 same tissues showed in A. The asterisk indicates S6k2 found in GAPDH the lymph node loaded as a control. C, Western blot analysis from the adrenal gland of 3 Lymph node Adrenal Uterus Heart Kidney different 13-month-old mice of the gland indicated genotypes. C wt Pten+/– Double

S6K1

S6K2

Pten

P-S6

GAPDH

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has a differential impact on specific phenotypes and in a across a panel of tissues. Previously published data have tissue-specific fashion. reported the mRNA for S6k1 and S6k2 to be ubiquitously Interestingly, an analysis of the effect of S6k1 inactivation expressed in all tissues analyzed (15–17). Indeed, using Taq- þ on uterine tumor formation in Pten / female mice, a less Man real-time PCR assays we confirmed the expression of penetrant phenotype in this background (5), leads to a mRNA for both genes in tissues obtained from wt mice, þ mildly reduced penetrance when compared with Pten / indicating that they are actively transcribed in all organs females alone (Supplementary Fig. S2). However, the reduc- tested (Fig. 2A). Surprisingly however, Western blot analysis ed penetrance is not as striking as that observed for the revealed a differential expression of the 2 proteins, with S6k2 adrenal glands. These data suggest that there may be in- levels found to vary profoundly (Fig. 2B and Supplementary complete redundancy between S6k1 and S6k2 in this tissue, Fig. S3). For example, comparing the amount of S6k2 protein which is in contrast to the complete redundancy observed between the lymph node and the adrenal gland shows strong þ with the lymph node phenotype of S6k1 / ;Pten / mice, differences in expression levels, whereas in contrast the S6k1 and again supports a tissue-specific role for the S6k1 and protein levels are comparable (Fig. 2B, left). In addition, it S6k2 proteins. should be noted that S6k2 showed clear protein expression in the uterus. These data suggest the existence of a posttran- Differential expression of S6k1 and S6k2 proteins in scriptional mechanism that fine-tunes the levels of the S6k2 mouse tissues protein in a tissue-specific manner. Additionally, we carried þ To understand the molecular basis underlying the tissue- out Western blot analysis on adrenal glands from wt, Pten / , þ specific differential response to deletion of S6k1, we decided to and S6k1 / ;Pten / mice and observed that S6k2 protein þ analyze in depth the expression status of both S6k1 and S6k2 levels did not increase in the S6k1 / ;Pten / glands (Fig. 2C).

S6K2 A S6K1

S6K2

GAPDH

Kidney ×20 ×20

AdrenalHum glandan cell line Kidney Adrenal gland

Figure 3. S6K1 and S6K2 protein expression in human tissues. A, B S6K1 left, Western blot analysis on human tissues lysates. As a control we have used a lysate from MCF7 human cell line. Right, IHC with anti-S6K2 on normal human tissues. B, staining with anti-S6K 60 (n = 9) on 16 cases of human ×20 ×20 50 pheochromocytoma. S6K1 immunostaining was scored as Score 0 Score 1 40 negative (0), weak (1), moderate 30 (2), or strong (3). C, phylogenetic cases of % 20 (n = 3) (n = 3) tree indicates the relationship and evolutionary descent of 10 (n = 1) various species based on protein 0 sequence of S6K1 and S6K2. 0123 ×20 ×20 Specifically, RPSKb-1 refers Intensity of staining to S6K1 protein and RPSKb-2 Score 2 Score 3 to S6K2.

G.gallusRPS6K C D.rerioRPS6K R.norvegicusRPSKbeta-2 M.musculusRPS6Kbeta-2 B.taurusRPSKbeta-2 HumanRPSKbeta-2 X.laevisRPS6Kb-1 M.musculusRPS6Kbeta-1 R.norvegicusRPSKbeta-1 O.cuniculusRPSKbeta-1 B.taurusRPSKbeta-1 H.sapiensRPS6Kbeta-1

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This finding indicates that S6k2 does not compensate for the of S6K1 (Fig. 3B), suggesting that targeting of this kinase may loss of S6k1 expression in this tissue. represent a potential avenue for treatment of this tumor. Takentogether,thesedataofferanexplanationforwhy S6k1 deletion has a differential impact on the phenotypes Discussion dictated by Pten heterozygosity. The minimal effect of S6k1 loss on uterine tumor formation and the lack of an effect on Overall, our data are in agreement with a model whereby lymph node proliferation may be accounted for through the response of Pten heterozygous phenotypes to the genetic compensation and redundancy with S6k2, whereas S6k1 deletion of S6k1 is tissue specific. This specificity may be deletion has a pronounced effect on the pheochromocytoma dictated by the relative protein expression of S6k2. Impor- incidence due to low protein expression of S6k2 in the tantly, we have shown that S6K2 protein levels vary drama- adrenal gland. tically between different tissues, in humans as well as in mice, whereas S6K1 is less susceptible to such extreme differences in Analysis of S6K1 and S6K2 protein expression in human protein expression. A phylogenetic analysis shows that S6K1 tissues is the ancestral kinase (Fig. 3C) and that S6K2 is only found Given the surprising finding that S6k2 protein levels were in mammalian organisms (15). This suggests that S6K2 may differentially expressed in the mouse, we sought to uncover have arisen at a later time and underscores our observation if this was also the case for the human adrenal gland and regarding the protein expression level of S6K1 relative to that kidney, the 2 mouse tissues that showed dramatically for S6K2 across multiple tissues, highlighting the importance reduced S6k2 expression. It has been previously reported of S6K1 for therapeutic targeting. that both S6K1 and S6K2 are ubiquitously expressed in Specifically, our data constitute the rationale to develop an humans at the mRNA level (16). However, as we showed S6K1-specific inhibitor to target tumors triggered by loss of in the mouse, Western blot analysis of human adrenal gland PTEN in tissues having low expression of S6K2. The precise revealed dramatically reduced S6K2 protein expression targeting of S6K1 in such tissues allows for inhibition of (Fig. 3A, left). In contrast, the human kidney tissue showed signaling downstream of mTORC1, while avoiding a general a relatively high S6K2 protein level, unlike our findings in toxicity due to inhibition of both in normal tissues, as sug- mouse. This result was further confirmed by IHC (Fig. 3A, gested by the perinatal lethality of the S6k1 / ;S6k2 / mice. right). From these data it appears that not only S6k2 protein An excellent example for such an S6K1 targeted therapy is expression can vary dramatically between different tissues represented by the treatment of pheochromocytoma, as is but also the tissue-specific pattern of expression can change clearly shown through our genetic inactivation of S6k1 in the þ between organisms. Although S6k2 protein levels were adrenal gland of Pten / mice and our concomitant human markedly different among the human tissues tested, we data. again found S6K1 protein expression to be more consistent (Fig. 3A). This finding further highlights the key role of S6K1 Disclosure of Potential Conflicts of Interest in signaling downstream mTORC1 in the human adrenal gland, as is the case for the mouse. No potential conflicts of interest were disclosed. Given that our data in mouse indicate a pivotal role for S6K1 in the proliferation of the adrenal medulla, and the fact that Acknowledgments the human adrenal gland expresses mainly S6K1, we decided to analyze the protein expression status of S6K1 in human The authors thank Leonardo Salmena and all the members of the Pandolfi laboratory for discussion and comments. They also thank Priyanka B. Patel and pheochromocytoma. We carried out IHC analysis on a number Kaitlyn Webster for their technical help with the histologic work. of human pheochromocytoma cases. Staining of S6K1 over- expression was quantified using a scale going from negative Grant Support (0), weak (1), moderate (2) to strong (ref. 3; Fig. 3B). The vast majority of pheochromocytoma cases expressed S6K1 at This work is supported through MMHCC (Mouse Models of Human Cancers various levels (Fig. 3B), whereas the normal adjacent tissue Consortium) and NCI (National Cancer Institute) grants (5U01CA141464-02 and – CA082328-12). scored as very weak (i.e., 0 1) for S6K1 expression (Supple- The costs of publication of this article were defrayed in part by the payment mentary Fig. S4). Although these data may be limited by a lack of page charges. This article must therefore be hereby marked advertisement in of additional information regarding the genetic determinants accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

underlying these tumors, it is important to note that 25% Received November 1, 2010; revised February 21, 2011; accepted March 3, (4 of 16) of the pheochromocytomas showed very high levels 2011; published OnlineFirst March 28, 2011.

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Differential Expression of S6K2 Dictates Tissue-Specific Requirement for S6K1 in Mediating Aberrant mTORC1 Signaling and Tumorigenesis

Caterina Nardella, Andrea Lunardi, Giuseppe Fedele, et al.

Cancer Res Published OnlineFirst March 28, 2011.

Updated version Access the most recent version of this article at: doi:10.1158/0008-5472.CAN-10-3962

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