Insulin-like growth factors (IGF1 and IGF2), insulin and some insulin therapies promote intestinal growth but are also linked to colorectal cancer (CRC) and increased CRC risk in obesity or diabetes. The IGF1 receptor, (IGF1R), and insulin receptor (IR) mediate IGF and insulin action. The specific roles of IGF1R and IR in intestinal growth, CRC, obesity-associated CRC and intestinal epithelial stem cells (IESC) that drive tumor initiation are undefined. IGFs and insulin can each activate IGF1R or IR. Whether IGF1R or IR is activated depends on ligand levels, IGF1R and IR expression levels, whether receptors are homodimers or heterodimers, and levels of IR-A and IR-B isoforms of IR. IR-B mediates metabolic actions of insulin. IR-A regulates fetal growth and is up-regulated in some cancers. Preliminary data demonstrate expression patterns of IGF1R, IR-A and IR-B, which predict distinct roles of these receptors in IESC and differentiated cells. Mice with Villin-Cre (VC) mediated deletion of IGF1R (VC-IGF-IR(/( ) or IR (VC-IR(/() and mice cross-bred with Lgr5- EGFP and Sox9-EGFP stem cell reporters, will be used to dissect the specific roles of IGF1R and IR in intestinal epithelium and normal or tumor-associated IESC.
Specific aims will test a central hypothesis that IGF1R is a major mediator of tumorigenesis in the intestinal epithelium, while IR normally limits tumorigenesis and promotes differentiation or differentiated function.
Aim 1 will define the effects of intestinal epithelial deletion of IGF1R on intestinal tumorigenesis and hormone induced growth. Azoxymethane (AOM) and ApcMin/+ models will be used to confirm preliminary data that VC-IGF1R(/( mice show dramatic reductions in early precancerous lesions. Treatment with IGFs, insulin or a long-acting insulin-glargine linked to CRC will define if IGF1R is required for growth or tumor- promoting effects of hormones, or if IR can mediate these effects.
Aim 2 will define the effects of intestinal epithelial deletion of IR on intestinal tumorigenesis and hormone induced growth. AOM and ApcMin/+ models will be used to test the hypothesis that VC-IR(/( mice will show enhanced or accelerated early stage tumorigenesis. Treatment with IGF1 or insulin-glargine will test if loss of IR enhances hormone-induced IGF1R activation, growth or tumorigenesis.
Aim 3 will define whether IGF1R or IR mediate the effects of high fat diet (HFD)-induced hyperinsulinemia and obesity on intestinal growth or tumorigenesis. IESC reporter mice and VC- IGF1R(/( and VC-IR(/( mice, will be used to define the effects of HFD on IESC, or adaptive changes in growth or differentiation and test whether IGF1R or IR mediate these effects, or the tumor-promoting effects of diet- induced obesity Each aim will define molecular mechanisms associated with loss of IGF1R or IR in IESC, normal epithelium, tumors or stem cells. Our findings will advance mechanistic understanding of the roles of IGF1R and IR in intestinal growth, stem cells and spontaneous or obesity-associated CRC
Insulin and insulin-like growth factors are essential to normal metabolism, growth and tissue repair. Excess levels of these hormones occur in obesity and some types of diabetes and increase risk of gastrointestinal cancers. This project will identify the receptors that drive beneficial growth effects or tumor promoting effects of the hormones. The aim is to identify safer, preventative strategies and therapies to combat gastrointestinal cancer and the cancer-promoting effects of obesity and diabetes.
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