| Summary: | 碩士 === 國立中山大學 === 生物科學系研究所 === 96 === The TSG101 protein has been implicated in multiple biological functions including the regulation of gene transcription, vesicular trafficking, cellular growth and differentiation. Previous reports indicated the steady-state level of TSG101 must be maintained in a narrow range. Either deprivation or overexpression of TSG101 protein could result in neoplastic transformation. However, cellular signals that control TSG101 functions are not clear. TSG101 protein contains many kinase phosphorylation sites including two GSK-3β phosphorylation sites, S-172 (S172-P-Y-P-S176 ) and S202 (S202-Q-Y-P-S206). Our previous in vitro kinase assay result indicated TSG101 could be phosphorylated by GSK-3β. In the present study, we demonstrated that 47 kDa TSG101 is monoubiquitination of 42 kDa TSG101. The GSK-3β inhibitors, LiCl and TDZD8 could decrease TSG101 level in both HeLa and HEp-2 cells. On the contrary, activation of GSK-3β by serum starvation or by transfection of a plasmid encodes for constitutive active GSK-3β led to the increase of TSG101 level in a dose-dependent manner. The effect of LiCl and TDZD8 could be blocked by MG132, implying the involvement of proteaosome mediated mechanism. Expression of constitutive active GSK-3bmutS9A led to a dose-dependent increases of wildtype and HA-TSG101mutS172176A, but decrease of HA-TSG101mutS202206A protein. In addition, either wildtype or mutant HA-TSG101 could complex with GFP-GSK-3b. The mutation of S202 GSK-3b phosphorylation site of TSG101 compromised its ability to for complex with GSK-3b. In summary, our data support that GSK-3b is an important cellular signaling in regulation of monoubiquitinated TSG101 steady-state level. Whether it also affects the subcellular localization of TSG101 awaits further investigation.
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