RASSF1A inhibits estrogen receptor alpha expression and estrogen-independent signalling: implications for breast cancer development

Abstract

The Ras association domain family 1 isoform A (RASSF1A) is a tumor suppressor whose inactivation is implicated in the development of many human cancers, including breast carcinomas. Little is known about the tumor-suppressive function of RASSF1A in breast tissue and whether its inactivation is mechanistically involved in the initiation and progression of breast tumors. Here, we show that RASSF1A inhibits breast cancer growth in vivo, and suppresses estrogen receptor (ERa) expression and function. Reconstitution of RASSF1A in MCF7 cells led to decreased ERa levels and reduced sensitivity to estrogen (E2). Concomitantly, we observed decreased expression of Id1 as well as the E2-responsive genes Bcl-2 and c-Myc that cooperatively contribute to the immortalization and transformation of breast epithelial cells. This downregulation was associated with induction of cell-cycle arrest and senescence that constitute early barriers to cancer initiation and progression. Knockdown of ERa showed that downregulation of ERa suffices to increase senescence and inhibit expression of Bcl-2, c-Myc and Id1. However, enforced expression of ERa only partially rescued RASSF1A-mediated growth inhibition and senescence, suggesting that suppression of ERa expression and activity is not the only mechanism by which RASSF1A inhibits growth and survival of breast cancer cells. Ectopic expression of Bcl-2, c-Myc and Id1 had little or no effect on RASSF1A-mediated growth arrest, indicating that RASSF1A acts dominantly over these oncogenes. Mechanistically, RASSF1A was found to suppress ERa expression through Akt1. It also transiently inhibited ERa-induced Ras-MAPK activity after exposure of cells to E2. Together, our data show that RASSF1A acts as a tumor suppressor in ERa þ mammary epithelial cells, in part through inhibiting ERa expression and activity. These findings suggest that RASSF1A has a key role in suppressing the transformation of human breast epithelial cells and ERa þ breast cancer initiation.

CXCL12 and ADAM23 hypermethylation are associated with advanced breast cancers

“…These findings indicate a hormonal regulation of the DNA methylation process, which is visible in the hypermethylated genes and in the functional relationship between the individual genes and the hormone receptors, as was previously observed in an in vitro study showing that RASSF1A regulated ER expression in an estrogen-independent manner. 49 This association was supported by our finding of positive correlation between RASSF1A methylation levels and the percentage of cancer cells expressing ER and PR in BC samples. 40 During the progression of BC, many combinations of genetic and epigenetic changes occur, resulting in mutations or altered gene expression.…”

Genetic and epigenetic mutations of tumor suppressive genes in sporadic pituitary adenoma

“…In addition, RASSF1 induces cell cycle arrest by induction of p21 Cip1 independent of p53 (Thaler et al, 2009). Finally, RASSF1 represses expression of ERα, inhibiting estrogen independent signaling (Thaler et al, 2012). These data indicate that RASSF1 may suppress tumor growth via multiple pathways.…”

Aberrant Methylation of RASSF1A gene Contribute to the Risk of Renal Cell Carcinoma: a Meta-Analysis

“…The function of RASSSF1A is associated with cell cycle, apoptosis and microtubule (Agathanggelou , 2005). RASSF1A is a putative tumor suppressor gene (TSG) and can suppress the tumorigenic properties of different kinds of tumors (Thaler et al, 2012;Feng et al, 2014). It has the potential to be a predictor of RCC.…”