| Summary: | 碩士 === 中山醫學大學 === 醫學研究所 === 91 === Abstract
Extracellular matrix (ECM) affects a number of cellular responses through modulation of growth factor signaling. For mammary epithelia, insulin-stimulated signaling is propagated properly when cells are in contact with basement membrane, but it is hindered when cells are cultured on plastic or collagen I. Under the latter situation, tyrosine phosphorylation of insulin receptor (IR) is not affected but phosphorylation of insulin receptor substrate-1 (IRS-1) is substantially impaired. Therefore, a novel ECM-dependent control point in insulin signaling is at the level of tyrosine phosphorylation of IRS-1. In this study, we investigated into the regulatory mechanisms for insulin signaling in mammary epithelial cells, especially focusing on the membrane proximal events. We found that insulin signaling probably did not take place in lipid rafts since disruption of them exerted no effect on signaling; however, cytoskeleton integrity was critical for it. Incubation of aspirin and PGJ2 that have been shown to revert insulin resistance did not increase the extent of IRS-1 tyrosine phosphorylation. By contrast, inhibition of phosphatidylinositol 3 kinase (PI3K) by wortmannin led to greater degree of IRS-1 recruitment to the receptor, and tyrosine phosphorylation of IRS-1, especially for those cells cultured on plastic. This suggests that the inertness of the cells cultured on plastic to insulin signaling is probably mediated by PI3K. Lastly, we examined the expression of protein tyrosine phosphatases (PTP) in cells cultured on plastic and basement membrane as it plays an important role in controlling the homeostasis of tyrosine phosphorylation. We found that the levels of PTP1B, SHP-2 and RPTP were comparable in cells on both substrata, but the expression of LAR was more prominent in cells cultured on BM. Thus, we were still not clear which PTP might be involved in regulation of insulin signaling in cells cultured on plastic.
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