More than 600,000 people die from Hepatocellular carcinoma (HCC) worldwide annually. The environmental factors that cause HCC are well known and include infection by hepatitis B and C viruses (HBV and HCV), exposure to Aflatoxin B1, and excessive alcohol intake. However, no effective treatments exist for HCC and the prognosis of HCC patients is usually poor, with an overall median survival of less than one year. The RB tumor suppressor and its family member's p107 and p130 are functionally inactivated in nearly all cases of human HCC. This inactivation is due to increased CDK4 kinase activity resulting from the silencing of the CDK4 inhibitor p16 or from increased expression of the CDK4 partner Cyclin D1. In addition, some proteins produced by HBV and HCV can inactivate RB family members, including by triggering their degradation. We generated a mouse model for human HCC by deleting RB family genes in the liver of adult mice to model this functional inactivation of RB family proteins. RB/p107/p130 triple knockout (TKO) mice develop liver tumors whose histology and gene expression profiles resemble human HCCs. The activity of E2F transcription factors, which are normally inhibited by the RB family, is high in TKO HCC cells. TKO HCCs initiate from progenitor cells and not hepatocytes, which do not divide due to unknown mechanisms that suppress their proliferation. The TKO HCC model provides a unique in vivo system to query the mechanisms of tumorigenesis in the liver and to specifically interrogate how RB/E2F transcriptional regulatory complexes control HCC development. Our general hypothesis is that inactivation of the RB pathway drives cancer initiation at least in part by deregulating E2F activity and compromising the balance between regulatory networks in acutely sensitive cell populations. Specifically, we propose that increased E2F activity engages pathways that promote the expansion of mutant cells, including liver progenitors, but also triggers negative feedback loops preventing cancer initiation from mature hepatocytes and limiting the growth of HCC cells. We will first test the specific hypothesis that activation of p21 by E2F in the TKO model blocks the proliferation of hepatocytes, thereby preventing HCC initiation from these mature cells. Next, we will test the idea that activation of Notch signaling y E2F limits the expansion of HCC cells during tumorigenesis. Finally, we will examine the possibility that activation of the EZH2 methyltransferase by E2F promotes the growth of both liver progenitors and HCC cells. To test these hypotheses, we will manipulate the activity of RB and E2F family members, p21 and CDK2, Notch pathway members, and EZH2 in adult liver progenitor cells, mature hepatocytes, and HCC cells in vivo. These experiments in mutant mice will be complemented by analyses of human liver cells ex vivo. Our studies will identify novel means to diagnose, detect, and treat HCC. In addition, because genetic, epigenetic, and/or viral inactivation of the RB pathway is a nearly universal event in human cancer cells, these studies are generally relevant to a broad cross-section of cancer patients.
Hepatocellular carcinoma (HCC) is a malignant tumor of the liver that develops in patients with risk factors such as alcohol abuse, viral hepatitis, and metabolic liver disease;most HCC patients die within one year of diagnosis. Our goal is to develop and study mouse models of HCC associated with loss of function of the RB pathway, a common event in human HCC, to gain a better understanding of the molecular and cellular mechanisms underlying HCC development. We hope that the results of these studies will help identify novel means to diagnose, detect, and treat HCC in patients.
|Ehmer, Ursula; Sage, Julien (2016) Control of Proliferation and Cancer Growth by the Hippo Signaling Pathway. Mol Cancer Res 14:127-40|
|Kareta, Michael S; Gorges, Laura L; Hafeez, Sana et al. (2015) Inhibition of pluripotency networks by the Rb tumor suppressor restricts reprogramming and tumorigenesis. Cell Stem Cell 16:39-50|
|George, Julie; Lim, Jing Shan; Jang, Se Jin et al. (2015) Comprehensive genomic profiles of small cell lung cancer. Nature 524:47-53|
|Kareta, Michael S; Sage, Julien; Wernig, Marius (2015) Crosstalk between stem cell and cell cycle machineries. Curr Opin Cell Biol 37:68-74|
|Xu, Lei; Hazard, Florette K; Zmoos, Anne-Flore et al. (2015) Genomic analysis of fibrolamellar hepatocellular carcinoma. Hum Mol Genet 24:50-63|
|Ehmer, Ursula; Zmoos, Anne-Flore; Auerbach, Raymond K et al. (2014) Organ size control is dominant over Rb family inactivation to restrict proliferation in vivo. Cell Rep 8:371-81|
|Ntziachristos, Panagiotis; Lim, Jing Shan; Sage, Julien et al. (2014) From fly wings to targeted cancer therapies: a centennial for notch signaling. Cancer Cell 25:318-34|
|Santos, Mirentxu; MartÃnez-FernÃ¡ndez, MÃ³nica; DueÃ±as, Marta et al. (2014) In vivo disruption of an Rb-E2F-Ezh2 signaling loop causes bladder cancer. Cancer Res 74:6565-77|
|Attardi, Laura D; Sage, Julien (2013) RB goes mitochondrial. Genes Dev 27:975-9|
|Sage, Julien (2012) The retinoblastoma tumor suppressor and stem cell biology. Genes Dev 26:1409-20|
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