| Summary: | 碩士 === 中山醫學大學 === 醫學研究所 === 95 === Optimal prolactin signaling in mammary epithelial cells requires cell adhesion to basement membrane. However, the underlying mechanism remains obscure. Here we investigate into the role of the RhoA/Rho kinase (ROK) pathway in the regulation of prolactin signaling since lower RhoA activity has been detected in mammary cells cultured on basement membrane compared to those cultured on plastic. Firstly, we have demonstrated that expression of prolactin receptor mRNA is influenced by substrata. Cells cultured on basement membrane exhibit higher level of prolactin receptor mRNA. Furthermore, overexpression of activated RhoA (L63RhoA) in cells cultured on basement membrane reduces prolactin receptor mRNA level, prolactin-induced Stat5 tyrosine phosphorylation and the downstream β-casein gene expression. On the contrary, overexpression of dominant negative RhoA (N19RhoA) in cells cultured on plastic results in the elevation in levels of prolactin receptor mRNA and of Stat5 phosphorylation. Similar results were obtained by expressing dominant negative ROK and application of the ROK inhibitor Y27632 in these cells. Inclusion of Y27632 in cells cultured on plastic also exerts a positive effect on Rac activity, leading to an increase in Rac activity. Thus, the RhoA/ROK pathway is, at least in part, responsible for the inefficiency of prolactin signaling in mammary cells cultured on plastc.
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