The Tumor Suppressor Gene, RASSF1A, Is Essential for Protection against Inflammation -Induced Injury

Abstract

Ras association domain family protein 1A (RASSF1A) is a tumor suppressor gene silenced in cancer. Here we report that RASSF1A is a novel regulator of intestinal inflammation as Rassf1a+/−, Rassf1a−/− and an intestinal epithelial cell specific knockout mouse (Rassf1a IEC-KO) rapidly became sick following dextran sulphate sodium (DSS) administration, a chemical inducer of colitis. Rassf1a knockout mice displayed clinical symptoms of inflammatory bowel disease including: increased intestinal permeability, enhanced cytokine/chemokine production, elevated nuclear factor of kappa light polypeptide gene enhancer in B-cells (NFκB) activity, elevated colonic cell death and epithelial cell injury. Furthermore, epithelial restitution/repair was inhibited in DSS-treated Rassf1a−/− mice with reduction of several makers of proliferation including Yes associated protein (YAP)-driven proliferation. Surprisingly, tyrosine phosphorylation of YAP was detected which coincided with increased nuclear p73 association, Bax-driven epithelial cell death and p53 accumulation resulting in enhanced apoptosis and poor survival of DSS-treated Rassf1a knockout mice. We can inhibit these events and promote the survival of DSS-treated Rassf1a knockout mice with intraperitoneal injection of the c-Abl and c-Abl related protein tyrosine kinase inhibitor, imatinib/gleevec. However, p53 accumulation was not inhibited by imatinib/gleevec in the Rassf1a−/− background which revealed the importance of p53-dependent cell death during intestinal inflammation. These observations suggest that tyrosine phosphorylation of YAP (to drive p73 association and up-regulation of pro-apoptotic genes such as Bax) and accumulation of p53 are consequences of inflammation-induced injury in DSS-treated Rassf1a−/− mice. Mechanistically, we can detect robust associations of RASSF1A with membrane proximal Toll-like receptor (TLR) components to suggest that RASSF1A may function to interfere and restrict TLR-driven activation of NFκB. Failure to restrict NFκB resulted in the inflammation-induced DNA damage driven tyrosine phosphorylation of YAP, subsequent p53 accumulation and loss of intestinal epithelial homeostasis.

Netrin-1 exerts oncogenic activities through enhancing Yes-associated protein stability

“…Imaginably, the cancer cells can secrete the intracellular netrin-1 and activate the receptors on the plasma membrane via autocrine, leading to YAP signaling regulation. It is also reported that YAP activity in modulation of proliferation and senescence is regulated by Ras association domain family 1A (RASSF1A) (28) and RASSF4 (29), respectively. The RASSF family of proteins consists of 10 members, most of which are considered as tumor suppressor proteins that undergo loss of expression through promoter methylation in various types of cancers.…”

RASSF tumor suppressor gene family: Biological functions and regulation

“…We also recently demonstrated that, under conditions of acute intestinal inflammation, RASSF1A restricts NFjB activity by interfering with the ability of the membrane proximal TLR/MyD88/TRAF6/IRAK2/4 complex to promote downstream signaling to NFjB [46]. The restriction of NFjB activity also led to restriction of tyrosine (Y) 357 phosphorylation of Yes associated protein (YAP), a key Hippo-dependent transcription factor linked to proliferation [46]. We determined that Y357 phosphorylation of YAP may arise due to increased inflammation and DNA damage -both of which are prominent during intestinal inflammation injury stimulated by the colonic irritant, dextran sodium sulfate (DSS) [46].…”

“…These associations function to prevent excessive growth and allow RASSF1A to function as a tumor suppressor. We also recently demonstrated that, under conditions of acute intestinal inflammation, RASSF1A restricts NFjB activity by interfering with the ability of the membrane proximal TLR/MyD88/TRAF6/IRAK2/4 complex to promote downstream signaling to NFjB [46]. The restriction of NFjB activity also led to restriction of tyrosine (Y) 357 phosphorylation of Yes associated protein (YAP), a key Hippo-dependent transcription factor linked to proliferation [46].…”

“…The restriction of NFjB activity also led to restriction of tyrosine (Y) 357 phosphorylation of Yes associated protein (YAP), a key Hippo-dependent transcription factor linked to proliferation [46]. We determined that Y357 phosphorylation of YAP may arise due to increased inflammation and DNA damage -both of which are prominent during intestinal inflammation injury stimulated by the colonic irritant, dextran sodium sulfate (DSS) [46]. We are currently exploring the molecular mechanisms modulating the Y357 phosphorylation of YAP and of its importance for the appearance and/or progression of inflammatory bowel disease.…”

“…Recently, we showed that Rassf1a À/À mice are susceptible to DSS-induced colitis [46]. Rassf1a À/À mice displayed clinical symptoms of inflammatory bowel disease (IBD) including increased intestinal permeability, enhanced cytokine/chemokine production, elevated NFjB activity and elevated colonic cell death and epithelial cell injury [46].…”