ABSTRACT
SOX transcription factors have the capacity to modulate stem/progenitor cell proliferation and differentiation in a dose-dependent manner. SOX9 is expressed in the small intestine epithelial stem cell zone. Therefore, we hypothesized that differential levels of SOX9 may exist, influencing proliferation and/or differentiation of the small intestine epithelium. Sox9 expression levels in the small intestine were investigated using a Sox9 enhanced green fluorescent protein (Sox9(EGFP)) transgenic mouse. Sox9(EGFP) levels correlate with endogenous SOX9 levels, which are expressed at two steady-state levels, termed Sox9(EGFPLO) and Sox9(EGFPHI). Crypt-based columnar cells are Sox9(EGFPLO) and demonstrate enriched expression of the stem cell marker, Lgr5. Sox9(EGFPHI) cells express chromogranin A and substance P but do not express Ki67 and neurogenin3, indicating that Sox9(EGFPHI) cells are postmitotic enteroendocrine cells. Overexpression of SOX9 in a crypt cell line stopped proliferation and induced morphological changes. These data support a bimodal role for SOX9 in the intestinal epithelium, where low SOX9 expression supports proliferative capacity, and high SOX9 expression suppresses proliferation.
Subject(s)
Cell Differentiation , Cell Proliferation , Enteroendocrine Cells/metabolism , Intestinal Mucosa/metabolism , Intestine, Small/metabolism , SOX9 Transcription Factor/metabolism , Stem Cells/metabolism , Animals , Cell Differentiation/genetics , Cell Line , Cell Shape , Chromogranin A/metabolism , Gene Expression Regulation , Genes, Reporter , Genotype , Intestinal Mucosa/cytology , Intestine, Small/cytology , Mice , Mice, Transgenic , Paneth Cells/metabolism , Phenotype , Rats , Receptors, G-Protein-Coupled/metabolism , SOX9 Transcription Factor/genetics , Substance P/metabolism , Transduction, GeneticABSTRACT
Reduced apoptosis of crypt stem/progenitor cells and elevated insulin and IGFs are linked to colon cancer risk. Insulin receptor substrate-1 (IRS-1) mediates the actions of insulin, IGF-I, and IGF-II, but the role of endogenous IRS-1 in crypt apoptosis and cancer is undefined. Using IRS-1(-/-), IRS-1(+/-), and IRS-1(+/+) mice, we tested the hypothesis that reduced IRS-1 expression increases apoptosis of intestinal crypt cells and protects against Apc(min/+) (Min)/beta-catenin-driven intestinal tumors. Expression of Sox9, a transcriptional target of Tcf/beta-catenin and putative biomarker of crypt stem cells, was assessed in intestine of different IRS-1 genotypes and cell lines. Irradiation-induced apoptosis was significantly increased in the crypts and crypt stem cell region of IRS-1-deficient mice. Tumor load was significantly reduced by 31.2 +/- 14.6% in IRS-1(+/-)/Min and by 64.1 +/- 7.6% in IRS-1(-/-)/Min mice, with more prominent reductions in tumor number than size. Compared with IRS-1(+/+)/Min, IRS-1(-/-)/Min mice had fewer Sox9-positive cells in intestinal crypts and reduced Sox9 mRNA in intestine. IRS-1 overexpression increased Sox9 expression in an intestinal epithelial cell line. We conclude that even small reductions in endogenous IRS-1 increase apoptosis of crypt stem or progenitor cells, protect against beta-catenin-driven intestinal tumors, and reduce Sox9, a Tcf/beta-catenin target and putative stem/progenitor cell biomarker.
