RASSF1A downregulates AREG by activation of Hippo pathway RASSF1A-mediated regulation of amphiregulin via the Hippo pathway in hepatocellular carcinoma

Ras association domain family 1 isoform A (RASSF1A) is a tumor suppressor and the methylation thereof is known to be involved in many human cancers including hepatocellular carcinoma (HCC). RASSF1A has been shown to suppress tumors via activation of components of the Hippo tumor suppressor pathway, including mammalian STE20-like kinase (MST). Amphiregulin (AREG), a target gene for Yes-associated protein (YAP), is a known oncogenic component of the Hippo pathway; however, the tumor suppressive effect of RASSF1A on AREG in regards to regulation of the Hippo pathway remains unclear in HCC. In this study, overexpression of RASSF1A in HCC cells (Hep3B, SK-Hep1, and PLC/PRF/5), which lack functional RASSF1A, significantly inhibited cell proliferation and induced apoptosis by activating the Hippo pathway. Consequently, overexpression of RASSF1A inhibited the oncogenic functions of YAP, leading to a significant reduction in AREG secretion via regulation of the Hippo pathway. In human study, greater expression of RASSF1A was observed in chronic hepatitis (CH)/cirrhosis than in HCC, whereas expression of YAP and AREG was higher in 81% and 86% of HCC than corresponding CH/cirrhosis, respectively. Furthermore, a gradual decrease in RASSF1A protein expression was detected as multistep hepatocarcinogenesis progressed from CH/cirrhosis, dysplastic nodules (DNs), toward HCCs, while the protein expression of YAP and AREG gradually increased. These findings give evidence to the regulation of YAP and AREG (YAP signature) by RASSF1A in human multistep hepatocarcinogenesis. In conclusion, our results suggest that RASSF1A might play a crucial role in HCC suppression by regulating AREG expression via activation of the Hippo tumor suppressor pathway, leading to inactivation of oncogenic YAP. on June 27, 2017. © 2013 American Association for Cancer Research. mcr.aacrjournals.org Downloaded from Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. Author Manuscript Published OnlineFirst on April 17, 2013; DOI: 10.1158/1541-7786.MCR-12-0665