Determination of IGFBP-3 and -4 mRNA Downregulation by HB-EGF

Miami University Oxford, Oxford OH

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Abstract

[unreadable] DESCRIPTION (provided by applicant): The primary goal of our laboratory is to understand the role of growth factors in diabetes. We will investigate the mechanisms of heparin-binding EGF-like growth factor (HBEGF) in the insulin-like signaling pathway. HB-EGF stimulates cell proliferation and is up-regulated in response to diabetic conditions (Lee et al., 1995). In order to investigate the role of HB-EGF in diabetes, we will induce diabetes in both HB-EGF transgenic mouse mice that over-expresses HB-EGF in the kidney (Provenzano et al., 2005) and an HB-EGF null mouse model (Jackson et al., 2003) which lack HB-EGF. The kidneys will be analyzed for renal hypertrophy, an early indicator of diabetes, prior to the onset of puberty and immediately after puberty. Furthermore, a second growth factor, insulin-like growth factor (IGF-I), an important mediator of growth, accumulates in the kidney under diabetic conditions. Serum and kidney IGF-I levels will be measured in diabetic and nondiabetic animals. IGF-I levels are in part regulated by insulin-like binding proteins (IGFBPs). We have previously demonstrated that HB-EGF transgenic mice downregulate IGFBP-3 and -4 specifically in the kidney. In light of these data, we will quantify IGFBP-1 -5 in the kidney of diabetic and nondiabetic HB-EGF transgenic and HB-EGF null mice to determine the effects of these IGFBPs on diabetes by HB-EGF. HB-EGF is a single membrane spanning protein that undergoes extensive proteolytic processing the results in both extracellular and intracellular domains that are each capable of stimulating cellular division. We will determine whether one or both of these domains are responsible for mediating the insulin-like effects or whether the insulin-like effects are solely mediated by proteolytic processing. To gain insight into the HB-EGF structural requirements for insulin-like signaling, we will individually disrupt each of the 3 disulfide bonds within the EGF-like domain to determine which of these disulfide [unreadable] bonds are necessary to elicit biological activity. In sum, this proposal outlines experiments that will determine the emerging role of HB-EGF in renal disease as a result of diabetes. [unreadable] [unreadable] [unreadable]