Abstract

Purpose
Ras association domain family 4 (RASSF4) is a putative tumor suppressor that is frequently inactivated in multiple human cancers. However, its candidacy as a suppressor in gastric tumorigenesis remains undefined. To understand the role for RASSF4 in gastric tumorigenesis, we investigated its expression status in cancer cell lines and tissues and regulatory role in tumor growth.
Materials and Method
RASSF4 expression was analyzed in 13 cancer cell lines and 20 carcinoma tissues using PCR and immunoblot assays. RASSF4 effect on cell proliferation and apoptosis was examined by flow cytometry, colony formation, and [³H]thymidine incorporation assays and its regulation of p53 was determined using cycloheximide chase, promoter reporter, and immunoprecipitation assays. Mouse xenograft assay was performed to verify RASSF4 effect on tumor growth and therapeutic response.
Results
RASSF4 expression is epigenetically inactivated in 8 of 13 (61.5%) cancer cell lines and 15 of 20 (75%) primary carcinomas. RASSF4 suppresses cell proliferation by inducing a G2/M cell-cycle arrest and enhances apoptotic response to therapeutic drugs. RASSF4 is induced in response to genotoxic agents to facilitate stress-induced apoptosis in a highly p53-dependent fashion. Mechanistically, RASSF4 stabilizes p53 through Chk2 activation and its apoptotic function is profoundly impaired by depletion of either p53 or Chk2. RASSF4 attenuates xenograft tumor growth and enhances tumor response to 5-FU. Clinically, RASSF4 expression correlates strongly with the overall survival of gastric cancer patients.
Conclusion
RASSF4 suppresses gastric tumor growth through the activation of the Chk2-p53 axis, illuminating the mechanistic consequence of its inactivation in gastric tumorigenesis.

• Keywords: Stomach neoplasms, Tumor suppressor, RASSF4, p53, Chk2, Apoptosis, Promoter methylation, Cell-cycle arrest