title: Unique impact of RB loss on hepatic proliferation: tumorigenic stresses uncover distinct pathways of cell cycle control.
abstract: The retinoblastoma (RB) tumor suppressor pathway is disrupted at high frequency in hepatocellular carcinoma. However, the mechanisms through which RB modulates physiological responses in the liver remain poorly defined. Despite the well established role of RB in cell cycle control, the deletion of RB had no impact on the kinetics of cell cycle entry or the restoration of quiescence during the course of liver regeneration. Although these findings indicated compensatory effects from the RB-related proteins p107 and p130, even the dual deletion of RB with p107 or p130 failed to deregulate hepatic proliferation. Furthermore, although these findings suggested a modest role for the RB-pathway in the context of proliferative control, RB loss had striking effects on response to the genotoxic hepatocarcinogen diethylnitrosamine. With diethylnitrosamine, RB deletion resulted in inappropriate cell cycle entry that facilitated secondary genetic damage and further uncoupling of DNA replication with mitotic entry. Analysis of the mechanism underlying the differential impact of RB status on liver biology revealed that, while liver regeneration is associated with the conventional induction of cyclin D1 expression, the RB-dependent cell cycle entry, occurring with diethylnitrosamine treatment, was independent of cyclin D1 levels and associated with the specific induction of E2F1. Combined, these studies demonstrate that RB loss has disparate effects on the response to unique tumorigenic stresses, which is reflective of distinct mechanisms of cell cycle entry.
authors.affiliation: Department of Cancer Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Reed
authors.forename: Christopher N
authors.initials: CN
authors.lastname: Mayhew
authors.forename: A Kathleen
authors.initials: AK
authors.lastname: McClendon
authors.forename: Erik S
authors.initials: ES
authors.lastname: Knudsen
mesh_terms: D000477:Alkylating Agents / Q000494:pharmacology*; D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects* / Q000235:genetics; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism; D004249:DNA Damage / Q000187:drug effects* / Q000235:genetics; D004261:DNA Replication / Q000187:drug effects / Q000235:genetics; D004052:Diethylnitrosamine / Q000494:pharmacology*; D050687:E2F1 Transcription Factor / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D008113:Liver Neoplasms / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D016160:Retinoblastoma Protein; D050720:Retinoblastoma-Like Protein p107 / Q000235:genetics / Q000378:metabolism; D050717:Retinoblastoma-Like Protein p130 / Q000235:genetics / Q000378:metabolism
chemical_list: D000477:Alkylating Agents; C530105:Ccnd1 protein, mouse; D050687:E2F1 Transcription Factor; C493754:E2f1 protein, mouse; C489485:Rbl1 protein, mouse; C493838:Rbl2 protein, mouse; D016160:Retinoblastoma Protein; D050720:Retinoblastoma-Like Protein p107; D050717:Retinoblastoma-Like Protein p130; D019938:Cyclin D1; D004052:Diethylnitrosamine