Summary: | 碩士 === 國立陽明大學 === 生物藥學研究所 === 91 === Protein methylation has been suggested to play pivotal roles in regulating diverse cellular processes. This is evident by our findings that protein methylation plays a crucial role in Ara-C inuced K-562 differentiation and calcium modulates methyl- transferase activity in in vitro methylation assays. In this study, I examined the role of calcium in modulation of protein methylation in vivo and in K-562 differentiation. Our results showed that depletion of cytosolic calcium dramatically affected protein methyltransferase activity in K-562 in a time- and dose-dependent manner. The altered methylation patterns were restored by the addition of calcium, suggesting that calcium modulated methyltransferase activity in K-562 cells. Moreover, Ara-C-induced erythroid differentiation, as detected by benzidine staining, was significantly suppressed by depletion of either intracellular or extracellular calcium, suggesting the involvement of calcium in Ara-C-induced differentiation. Suppression of differentiation caused by calcium depletion was associated with an inhibition of methyltransferase activity. In addition, the intracellular calcium concentration increased by three to four folds in K-562 cells upon Ara-C treatment. Taken together, our data suggested, for the first time, that calcium may regulate K-562 erythroid differentiation induced by Ara-C through modulating protein methylation. To investigate the molecular mechanisms through which calcium modulates protein methylation, protein kinase Ca, a protein kinase activated by calcium, was overexpressed in cells and the protein methylation patterns were assayed. Overexpression of PKCa caused a significant change in protein methylation patterns, concluding that a potential interplay between protein phosphorylation and protein methylation.
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