RB loss abrogates cell cycle control and genome integrity to promote liver tumorigenesis.
OBJECTIVE
The retinoblastoma (RB) tumor suppressor is functionally inactivated in most hepatocellular carcinomas (HCC), although the mechanisms by which RB suppresses liver tumorigenesis are poorly defined. We investigated the impact of RB loss on carcinogen-induced liver tumorigenesis.


METHODS
Mice harboring liver-specific RB ablation and normal littermates were exposed to the hepatocarcinogen diethylnitrosamine (DEN). The influence of RB loss on liver tumorigenesis was assessed by evaluating tumor multiplicity, proliferation, and genome integrity within tumors arising in RB-deficient and wild-type livers. In silico analyses were used to probe the association between gene expression signatures for RB loss and chromosomal instability and the ability of genes up-regulated by RB loss to predict the survival of human HCC patients.


RESULTS
RB deficiency significantly increased tumor multiplicity in livers exposed to DEN. Although hepatocytes in nontumor regions of DEN-exposed livers were quiescent regardless of RB status, tumors arising in RB-deficient livers were significantly more proliferative than those in normal livers and expressed high levels of RB/E2F target genes. Analysis of genes up-regulated by RB loss demonstrated significant overlap with a gene expression signature associated with chromosomal instability. Correspondingly, tumors arising in RB-deficient livers were significantly more likely to harbor hepatocytes exhibiting altered ploidy. Finally, gene expression analysis of human HCCs demonstrated that elevated expression of RB-regulated genes independently predicts poor survival.


CONCLUSIONS
RB deletion in the mouse liver enhances DEN-induced tumorigenesis, associated with increased hepatocyte proliferation and compromised genome integrity. Evaluation of RB status may be a useful prognostic factor in human HCC.
Mayhew
Christopher N
CN
Department of Cell and Cancer Biology, University of Cincinnati, Cincinnati, Ohio 45267-0521, USA.
Carter
Scott L
SL
Fox
Sejal R
SR
Sexton
Charlene R
CR
Reed
Christopher A
CA
Srinivasan
Seetha V
SV
Liu
Xiangdong
X
Wikenheiser-Brokamp
Kathryn
K
Boivin
Gregory P
GP
Lee
Ju-Seog
JS
Aronow
Bruce J
BJ
Thorgeirsson
Snorri S
SS
Knudsen
Erik S
ES
D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology*; D002453:Cell Cycle / Q000502:physiology*; D043171:Chromosomal Instability / Q000502:physiology; D004273:DNA, Neoplasm / Q000235:genetics; D004052:Diethylnitrosamine; D004195:Disease Models, Animal; D015972:Gene Expression Regulation, Neoplastic; D016678:Genome / Q000235:genetics / Q000502:physiology*; D008099:Liver / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D008113:Liver Neoplasms / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology*; D051379:Mice; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D010766:Phosphorylation; D011003:Ploidies; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism*
D004273:DNA, Neoplasm; D016160:Retinoblastoma Protein; D004052:Diethylnitrosamine