Sox9 regulates cell proliferation and is required for Paneth cell differentiation in the intestinal epithelium

Abstract

The HMG-box transcription factor Sox9 is expressed in the intestinal epithelium, specifically, in stem/progenitor cells and in Paneth cells. Sox9 expression requires an active β-catenin–Tcf complex, the transcriptional effector of the Wnt pathway. This pathway is critical for numerous aspects of the intestinal epithelium physiopathology, but processes that specify the cell response to such multipotential signals still remain to be identified. We inactivated the Sox9 gene in the intestinal epithelium to analyze its physiological function. Sox9 inactivation affected differentiation throughout the intestinal epithelium, with a disappearance of Paneth cells and a decrease of the goblet cell lineage. Additionally, the morphology of the colon epithelium was severely altered. We detected general hyperplasia and local crypt dysplasia in the intestine, and Wnt pathway target genes were up-regulated. These results highlight the central position of Sox9 as both a transcriptional target and a regulator of the Wnt pathway in the regulation of intestinal epithelium homeostasis.

MiniSOX9, a dominant-negative variant in colon cancer cells

“…How MiniSOX9, devoid of transactivation domain, can activate Wnt? It might be a consequence of SOX9 inhibition, because SOX9 upregulates ICAT (inhibitor of b-catenin and T-cell factor (TCF))/TCF interaction (Tago et al, 2000) and the Groucho-related corepressors TLE2-4 (Cavallo et al, 1998;Roose et al, 1998) in HT29Cl.16E cells (Bastide et al, 2007), as well as CEACAM1 , which binds to the armadillo repeats of b-catenin, thereby inducing its redistribution from the cytosol to the plasma membrane (Jin et al, 2008;Leung et al, 2008). Moreover, MiniSOX9 is able to activate the Wnt pathway on its own, through its capacity to bind to b-catenin and inducing b-catenin accumulation in the nucleus.…”

“…As SOX9 deleted of its transactivation domain represses wild-type SOX9 activity in colon cancer cells (Blache et al, 2004;Bastide et al, 2007;Zalzali et al, 2008), we reasoned that such variants may well be expressed in colon cancer cells. We thus looked for a SOX9 splice variant resulting in a protein without the transactivation domain encoded by exon3.…”

“…MiniSOX9 inhibits SOX9 activity, inhibits PKCa promoter activity and stimulates the Wnt/bcatenin pathway by interacting with b-catenin We previously showed that a truncated SOX9 protein (SOX9DC) lacking the transactivation domain inhibited the DNA-binding-dependent SOX9 activity and activated the canonical Wnt pathway (Blache et al, 2004;Jay et al, 2005;Bastide et al, 2007). To examine if MiniSOX9 behaves as SOX9DC, we first addressed the impact of MiniSOX9 on SOX9 activity using a reporter MiniSOX9 in colon tumor R Abdel-Samad et al construct in which luciferase expression is driven by SOX-binding sites (Jay et al, 2005).…”

“…SOX9 is overexpressed in tumors from many origins and particularly in colon (Blache et al, 2004;Jay et al, 2005), but its role in cancer appears mostly antioncogenic. SOX9 is a canonical Wnt/b-catenin response gene (Blache et al, 2004) that exerts a negative feedback control on this pathway in colon cells (Bastide et al, 2007). Moreover, SOX9 directly upregulates the tumor suppressor CEACAM1 (CarcinoEmbryonic Antigenrelated Cell Adhesion Molecule 1) in the intestine epithelium , while it downregulates the carcinoembryonic antigen (CEA or CEACAM5) in human colon carcinoma cells (Jay et al, 2005).…”

“…Moreover, SOX9 directly upregulates the tumor suppressor CEACAM1 (CarcinoEmbryonic Antigenrelated Cell Adhesion Molecule 1) in the intestine epithelium , while it downregulates the carcinoembryonic antigen (CEA or CEACAM5) in human colon carcinoma cells (Jay et al, 2005). SOX9 also increases apoptosis in colon tumor cells (Jay et al, 2005) and reduces cell proliferation rate, as illustrated by hyperplasia and dysplasia induced by Sox9 abrogation in the intestine epithelium (Bastide et al, 2007;Zalzali et al, 2008). The anti-proliferative activity of SOX9 was also evidenced in retinoid-treated breast cancer cell lines and melanomas (Afonja et al, 2002;Passeron et al, 2009;Muller et al, 2010).…”