| Summary: | 碩士 === 國立成功大學 === 生理學研究所 === 81 === Epidermal growth factor (EGF), a 53-amino acid polypeptide,
is a potent mitogen for proximal tubular cells. However, no one
has successfully demonstrated that EGF accelerated
proliferation of proximal tubular cells. Using primary culture
of rabbit proximal tubules, we recently found that EGF induced
37% increase in cell number of cultured proximal tubule cells
at day 5 approaching subconfluent stage, but did not
accelerate proliferation when added at the lag phase. Since
thymidine incorporation and cell cycle analysis have
demonstrated that no significant change is found after EGF
treatment, it clearly indicated EGF is not mitogen at this
phase. On the contrary,it reduced protein contents of cultured
proximal tubular cells dose-dependently.We further determined
whether the decrease in protein contents was caused by cell
floating, and our data confirmed the suspicion. Other growth
factors or mitogens, such as TGFa, aFGF, bFGF, IGF-1, ADP and
ATP,also induced cell floating in the same setting. Since we
also observed that there were cell floating and morphological
changes in cultured proximal tubular cells after 2-3 hr
incubation of 10 ng/ml EGF, we therefore proposed that the
cytoskeletal changes induced by EGF may lead to cell floating.
Using immunocytochemical methods to determine whether EGF
altered the appearance of actin, cytokeratin and b-tubulin, we
found that EGF, at the dose of 0.1 ng/ml and up induced
redistribution of actin, reorganization of cytokeratin
filaments and elongation of b-tubulin. TGFa, IGF-1, and bFGF
induced similar changes, but ADP did not. The underlying
mechanisms are to be elucidated. Interestingly, the minimal
dosage of EGF to induce cytoskeletal changes of proximal
tubules lies within the physiological range of plasma
concentration, suggesting that EGF play some roles in
maintenance of cell morphology.
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