The RASSF1A Tumor Suppressor Blocks Cell Cycle Progression and Inhibits Cyclin D1 Accumulation

Abstract

The RASSF1A locus at 3p21.3 is epigenetically inactivated at high frequency in a variety of solid tumors. Expression of RASSF1A is sufficient to revert the tumorigenicity of human cancer cell lines. We show here that RASSF1A can induce cell cycle arrest by engaging the Rb family cell cycle checkpoint. RASSF1A inhibits accumulation of native cyclin D1, and the RASSF1A-induced cell cycle arrest can be relieved by ectopic expression of cyclin D1 or of other downstream activators of the G₁/S-phase transition (cyclin A and E7). Regulation of cyclin D1 is responsive to native RASSF1A activity, because RNA interference-mediated downregulation of endogenous RASSF1A expression in human epithelial cells results in abnormal accumulation of cyclin D1 protein. Inhibition of cyclin D1 by RASSF1A occurs posttranscriptionally and is likely at the level of translational control. Rare alleles of RASSF1A, isolated from tumor cell lines, encode proteins that fail to block cyclin D1 accumulation and cell cycle progression. These results strongly suggest that RASSF1A is an important human tumor suppressor protein acting at the level of G₁/S-phase cell cycle progression.

We thank Woodring Wright, Rene Bernards, Charles Sherr, and Piotr Sicinski for some of the reagents used in these studies and for cyclin D1^−/− mice. We thank Dale Henry and Lesli Hasbini for excellent technical assistance.

This work was supported by NIH grant R01CA71443 (M.W.) and the Welch Foundation (M.W.). L.S. is supported by U.S. Department of Defense grant DAMD17-00-1-0439. Additional support was obtained from R01CA70896 (R.G.P.) and R01CA71618 (J.M.).