title: Hepatitis B virus X protein differentially regulates cell cycle progression in X-transforming versus nontransforming hepatocyte (AML12) cell lines.
abstract: Hepatitis B virus (HBV) X protein (pX) is implicated in hepatocarcinogenesis of chronically infected HBV patients. To understand mechanism(s) of pX-mediated cellular transformation, we employed two tetracycline-regulated, pX-expressing cell lines, constructed in AML12 immortalized hepatocytes: one a differentiated (3pX-1) and the other a de-differentiated (4pX-1) hepatocyte cell line. Only 3pX-1 cells undergo pX-mediated transformation, via sustained Ras-Raf-mitogen-activated protein kinase pathway activation. pX-nontransforming 4pX-1 cells display sustained, pX-dependent JNK pathway activation. To understand how pX mediates different growth characteristics in 3pX-1 and 4pX-1 cells, we report, herein, comparative cell cycle analyses. pX-transforming 3pX-1 cells display pX-dependent G(1), S, and G(2)/M progression evidenced by cyclin D(1), A, and B(1) induction, and Cdc2 kinase activation. pX-nontransforming 4pX-1 cells display pX-dependent G(1) and S phase entry, followed by S phase pause and absence of Cdc2 kinase activation. Interestingly, 4pX-1 cells exhibit selective pX-induced expression of cyclin-dependent kinase inhibitor p21(Cip1), tumor suppressor p19(ARF), and proapoptotic genes bax and IGFBP-3. Despite the pX-mediated induction of growth arrest and apoptotic genes and the absence of pX-dependent Cdc2 activation, 4pX-1 cells do not undergo pX-dependent G(2)/M arrest or apoptosis. Nocodazole-treated, G(2)/M-arrested 4pX-1 cells exhibit pX-dependent formation of multinucleated cells, similar to human T-cell lymphotropic virus type I Tax-expressing cells. We propose that in 4pX-1 cells, pX deregulates the G(2)/M checkpoint, thus rescuing cells from pX-mediated apoptosis.
authors.affiliation: Department of Basic Medical Sciences, Purdue University, West Lafayette, Indiana 47907-1246, USA.
authors.forename: Sook
authors.initials: S
authors.lastname: Lee
authors.forename: Chi
authors.initials: C
authors.lastname: Tarn
authors.forename: Wen-Horng
authors.initials: WH
authors.lastname: Wang
authors.forename: Sigeng
authors.initials: S
authors.lastname: Chen
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Hullinger
authors.forename: Ourania M
authors.initials: OM
authors.lastname: Andrisani
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D015153:Blotting, Western; D016203:CDC2 Protein Kinase / Q000378:metabolism; D002453:Cell Cycle; D002460:Cell Line; D002461:Cell Line, Transformed; D019925:Cyclin A / Q000378:metabolism; D019926:Cyclin B / Q000378:metabolism; D056744:Cyclin B1; D019938:Cyclin D1 / Q000378:metabolism; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D005434:Flow Cytometry; D005786:Gene Expression Regulation; D022781:Hepatocytes / Q000378:metabolism*; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism; D048055:Mitogen-Activated Protein Kinase 8; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D015739:Nocodazole / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013752:Tetracycline / Q000494:pharmacology; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured; D025803:Tumor Suppressor Protein p14ARF / Q000378:metabolism; D054334:Viral Regulatory and Accessory Proteins; D051028:bcl-2-Associated X Protein
chemical_list: D000970:Antineoplastic Agents; C494826:BAX protein, human; C534699:CCNB1 protein, human; C493956:CDKN1A protein, human; C534700:Ccnb1 protein, mouse; C417743:Cdkn2a protein, mouse; D019925:Cyclin A; D019926:Cyclin B; D056744:Cyclin B1; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D018972:Insulin-Like Growth Factor Binding Protein 3; D011500:Protein Synthesis Inhibitors; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D015534:Trans-Activators; D025803:Tumor Suppressor Protein p14ARF; D054334:Viral Regulatory and Accessory Proteins; D051028:bcl-2-Associated X Protein; C057628:hepatitis B virus X protein; D019938:Cyclin D1; D016203:CDC2 Protein Kinase; D048055:Mitogen-Activated Protein Kinase 8; D020928:Mitogen-Activated Protein Kinases; D013752:Tetracycline; D015739:Nocodazole