Hbx) Protein-Expressing Liver Cells

Oncogene (2000) 19, 5163 ± 5172 ã 2000 Macmillan Publishers Ltd All rights reserved 0950 ± 9232/00 $15.00 www.nature.com/onc Chemotherapeutic drug, adriamycin, restores the function of p53 protein in hepatitis B virus X (HBx) protein-expressing liver cells Chawon Yun1,5, Jae-Ho Lee1,5, Hyelee Park1, Yoon-Mi Jin2, Sun Park3, Kyoungsook Park4 and Hyeseong Cho*,1 1Department of Biochemistry, Ajou University School of Medicine, Wonchon-dong 5, Paldal-ku, Suwon 442-749, Korea; 2Department of Pathology, Ajou University Hospital, Suwon 442-749, Korea; 3Department of Microbiology, Ajou University School of Medicine, Suwon 442-749, Korea; 4Samsung Biomedical Research Institute, Center for Molecular Medicine, Seoul, Korea Hepatitis B virus X (HBx) protein implicated in the HBx is a multifunctional transactivator for various development of liver cancer may inhibit the function of viral and cellular genes (Natoli et al., 1995). Transacti- p53 tumor suppressor protein through cytoplasmic vation function of HBx involves both activation of retention of p53 protein. Here, we attempt to investigate signal transduction cascades and direct protein-protein whether the functional inhibition of p53 protein by HBx interactions. HBx can transactivate several signaling protein is reversible. First, we provide the evidence for transduction pathways including protein kinase C the association of endogenous p53 protein with HBx by (KekuleÈ et al., 1993), ras/raf/MAP kinase (Benn and co-immunoprecipitation in stable Chang cells that Schneider, 1994; Benn et al., 1996), Jak1 kinase (Lee express HBx protein in an inducible manner (ChangX- and Yun, 1998) and src kinase (Klein et al., 1999). In 34). By immuno¯uorescence microscopy, the major addition, HBx directly interacts with transcription location of p53 protein of ChangX-34 cells was machinery such as RNA polymerase (Cheong et al., con®rmed at the nuclear periphery as well as in the 1995), TATA-binding protein and TF IIB (Haviv et al., cytoplasm where HBx protein is mainly expressed. 1998) and other cellular proteins such as p53 tumor Surprisingly, anticancer drug, adriamycin induces the suppressor protein. Thus, the pleiotropic activity of nuclear translocation of p53 protein sequestered in the HBx may contribute to the modulation of gene cytoplasm. This change is accompanied by the restora- expression, which ®nally leads to the formation of tion of p53 activity, which results in increased transcrip- liver cancer. tional activity at the p53-responsive DNA elements as p53 protein is a common target site in molecular well as increase of p21WAF1 mRNA expression. Further, pathogenesis of DNA tumor virus. Many viral we observed the induction of cell death and G1 arrest in oncoproteins disrupt p53 activity through direct these cells upon adriamycin treatment regardless of HBx protein-protein interaction (Teodoro and Branton, expression. Together, we demonstrate that functional 1997). These include large T antigen of simian virus inhibition of p53 protein through its cytoplasmic 40 (Peden et al., 1989), E6 protein of human retention by HBx protein is reversible. These results papillomavirus (Schener et al., 1990; Thomas et al., may be extended into other tumors of which p53 activity 1996), E1B 55-kDa of adenovirus (Rubenwolf et al., is modulated by viral oncoproteins. Oncogene (2000) 19, 1997) and HBx protein of HBV (Wang et al., 1994; Lin 5163 ± 5172. et al., 1997). Direct association between HBx and p53 proteins is observed with HBx-GST fusion proteins in Keywords: HBx; p53; liver cancer; chemotherapeutic vitro or with in vitro translated proteins (Truant et al., drug; subcellular localization; cytoplasmic sequestra- 1995). This association is suggested to be responsible tion for the mutual interference in the transactivation by HBx and p53 (Lin et al., 1997), and for blocking p53 entry into the nucleus in the HBx transgenic mouse Introduction (Ueda et al., 1995). Moreover, these interactions may relieve the p53-mediated inhibition of viral replication Chronic infection by hepatitis B virus (HBV) is (Lee et al., 1995). Thus, it is a general idea that associated with high incidence of hepatocellular modulation of p53 activity in viral pathogenesis is a carcinoma (HCC). Among HBV gene products, prerequisite for persistent replication of viral DNA as hepatitis B virus (HBx) protein is likely to play a well as deranged cell cycle control in host cells. Despite causative role in the development of HCC. Introduc- the important role of p53 in viral pathogenesis, tion of HBx gene into rodent cells causes cellular however, no one has demonstrated in vivo association transformation (HoÈ hne et al., 1990) and the of HBx with p53 in liver cells. In addition, cytoplasmic transforming activity is con®rmed by the HBx localization of p53 protein is never observed in either transgenic mice, which developed HCC (Kim et al., human hepatoma cells or liver specimens with 1991). preneoplastic nodules and HCC (Henkler et al., 1995; Greenblatt et al., 1997). Therefore, in human liver, it remains unclear for the actual association of these proteins and subsequent eects in HBx-induced *Correspondence: H Cho hepatocarcinogenesis. 5The ®rst two authors have contributed equally Received 15 February 2000; revised 22 August 2000; accepted 30 p53 activity in cancer cells is an important factor in August 2000 determining ecient cell death evoked by chemother- Reversible p53 activity in HBx-expressing liver cells C Yun et al 5164 apeutic drug or radiation. Radiation or drug treatment without doxycycline treatment, whereas a signi®cant on cells results in an accumulation of p53 protein amount of HBx protein was co-immunoprecipitated probably through posttranscriptional modi®cation of with anti-p53 antibody upon doxycycline treatment p53 protein itself (Chresta et al., 1996). Accumulated (Figure 2a). The level of HBx protein in the 1/20 of the p53 induces a number of downstream target genes such lysates used for immunoprecipitation indicated that as Fas, Killer/DR5 or bax, thereby mediating most of HBx protein induced by doxycycline was apoptosis (McCurrach et al., 1997; MuÈ ller et al., bound to p53 molecules. The speci®city of the 1997; Houghton, 1999; Wu et al., 1999). Many cancer interaction was con®rmed by immunoprecipitating the cells, however, contain mutant p53 gene or nonfunc- tional p53 protein modulated by viral oncoproteins. Therefore, cellular responses to drug or radiation in those cancer cells are expected to be altered and inecient. In fact, drug treatment induces rapid apoptosis in cells with wild-type p53, but not in p53 null teratocarcinoma cells (Zamble et al., 1998). And it is assumed that cells with p53-binding viral oncoproteins behave as if they have mutant p53 gene. However, it has never been addressed in detail how wild-type p53 protein bound to viral oncoproteins responds to radiation or drug treatment. In the present study, we take advantage of using human liver cells stably expressing HBx protein and demonstrate the cytoplasmic sequestration of endogenous p53 protein in HBx-dependent manner. We also provide the evidence that p53-mediated cellular responses to chemotherapeutic drug can be restored in these cells. Results Figure 1 Western blot analysis of HBx and p53 protein Expression of HBx and p53 proteins in HBx-expressing expressions in ChangX-34 cells. (a) After ChangX-34 cells were Chang liver cells treated with 2 mg/ml of doxycycline (Dox) for 0 ± 72 h, the cell lysates were prepared using RIPA buer and subjected to SDS ± We have established HBx protein-expressing Chang PAGE. The immunoblot was performed using anti-HA antibody. liver cell line (ChangX-34 cells) in a doxycycline- The protein concentration in each cell lysate was normalized by inducible manner in which HBx was tagged with HA at the level of a-tubulin content. (b) ChangX-34 cells were treated with doxycycline for 24 h and extracted with RIPA buer. The the carboxyl-terminus. Basal expression of HBx protein supernatant (s) and the pellet (p) were subjected to SDS ± PAGE was observed even in the absence of doxycycline and subsequently immunoblotted using anti-HA antibody, anti- treatment. When the cells were stimulated with 2 mg/ p53 antibody and anti-a tubulin antibody ml of doxycycline, HBx mRNA increased by more than 50-fold in a time-dependent manner (Kang H-J et al., submitted). The maximal increase of HBx protein was observed at 24 h after treatment and remained high up to 72 h (Figure 1a). Densitometry analysis demonstrated that HBx protein increased up to 7 ± 10- fold after normalization to the constitutive a-tubulin content. We next examined expression of p53 protein in these cells. Since Chang liver cells were known to contain wild-type p53 protein (Kim et al., 1998a), we used a combination of several anti-p53 antibodies to increase the sensitivity of detection. When the cells were extracted with RIPA buer, both HBx and p53 proteins were detected in the supernatant (Figure 1b). The expression level of p53 protein in these cells was not changed after treatment with doxycycline. HBx protein associates with p53 protein in ChangX-34 cells Figure 2 Co-immunoprecipitation of HBx and p53 proteins in ChangX-34 cells. (a) The cell lysates prepared from ChangX-34 To investigate the interaction between HBx and p53 cells were incubated with anti-p53 antibody and the immunopre- proteins, the total cell lysates of ChangX-34 cells were cipitates were analysed by Western blot using anti-HA antibody immunoprecipitated with anti-p53 antibody and

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