| Summary: | 碩士 === 國立成功大學 === 生理學研究所 === 92 === We previously showed that substratum rigidity down-regulated the expression of focal adhesion complex proteins such as FAK, paxillin and talin. However, the physiological significance of this finding has not been explored. Intact FAK remained constant levels in brain, heart, lung and liver throughout development and maturation. In contrast, we found that FAK was initially degraded into 100 kDa, 90 kDa and 85 kDa N-terminal fragments from embryonic 19.5 day and subsequently the intact
FAK was completely absent after birth in kidney. Other focal adhesion complex proteins such as paxillin, p130cas and cytosolic protein c-src were
also down-regulated during kidney development. To determine whether substratum rigidity affect expression of FAK, We employed primary culture of renal proximal tubular cells freshly isolated from 3-month-old rat kidney. Proximal tubular cells cultured on normal dish and collagen gel-coated dish exhibited focal adhesion complex proteins. However, collagen gel prevented the re-expression of focal adhesion complex proteins in primary culture. The expression level of FAK mRNA was not
altered in developmental kidney or in primary proximal tubular cells cultured on different rigidity, suggesting that the regulation of expression of FAK was mediated by post-transcriptional mechanism. Immunohistochemical study showed that FAK immunostaining were present in interstitial cells, but lost in developing nephrons in embryonic kidney. After birth, FAK immunostaining were completely absent in renal
cortex and expressed mostly in epithelial cells in inner medulla. Interestingly, nuclear localization of FAK immunostaining was quite prominent in mature kidney medulla, indicating the role of 85 kDa species in nuclear translocation. In addition, the phosphorylation at Y397, Y407 and Y577 of N-terminal FAK remained high in renal medulla during kidney maturation. Taken together, this study demonstrated that the rigidity might be involved in down-regulation of focal adhesion complex protein in developing kidney. Sumoylation of FAK may be the cases of phosphorylation of N-terminal FAK and translocation of N-terminal FAK
into nucleus of medullar tubular cells during kidney maturation.
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