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Biomedical subjects

W Bai

Publications and source records attributed to W Bai.

7 recordsLinked to original sources
PubMed1995

Phosphorylation and progesterone receptor function.

Four phosphorylation sites have been identified in the chicken progesterone receptor. Two of these sites exhibit basal phosphorylation which is enhanced upon treatment with hormone and two of the sites are phosphorylated in response to hormone. Mutation of one of these hormone dependent sites, Ser530 to Ala530, causes a decrease in transcriptional activation at low concentrations of hormone, but the activity is unaffected at high concentrations. However, the hormone binding of the mutant is unaffected suggesting that phosphorylation of Ser530 plays a role in facilitating the response of the receptor to low concentrations of hormone. The chicken progesterone receptor can be activated by modulators of kinases in the absence of hormone. The finding that signals initiated by tyrosine phosphorylation (through treatment with EGF) or through the dopamine receptor suggests that there are multiple means of activating chicken progesterone receptor. In contrast, the human progesterone receptor does not exhibit ligand independent activation; however, its activity in the presence of the agonist R5020 is enhanced by treatment with 8-Br-cAMP, an activator of protein kinase A, and treatment with 8-Br-cAMP causes the antagonist, RU486, to act as an agonist.

Amino Acid Sequence↗
PubMed1994

Phosphorylation of Ser530 facilitates hormone-dependent transcriptional activation of the chicken progesterone receptor.

Phosphorylation regulates the activities of many proteins, including transcription factors. However, the evidence for the significance of phosphorylation in steroid hormone receptor action is mainly indirect. In this study, one of the hormone-induced phosphorylation sites of chicken progesterone receptor, Ser530, was mutated to alanine, a nonphosphorylatable amino acid, and the transcriptional activity of the mutant receptor was compared with that of wild type in a transient cotransfection assay. The results showed that this mutation resulted in reduced transcriptional activity of chicken progesterone receptor at low hormone concentrations but did not affect the maximal activity of the receptor at saturating levels of hormone, suggesting that the phosphorylation at Ser530 influences the response of the receptor to its ligand. The decreased sensitivity of the mutant receptor is not due to a decrease in hormone-binding affinity, leading to our hypothesis that Ser530 phosphorylation stabilizes the receptor in its active state, perhaps by preventing its reassociation with heat shock proteins or by maintaining a conformation suitable for interaction with other transcription factors.

Animals↗
PubMed1994

Multiple signaling pathways activate the chicken progesterone receptor.

We have previously reported that treatment of CV1 cells, transiently transfected with DNA encoding the chicken progesterone receptor (cPR) and a reporter plasmid PREtkCAT, with either 8-Br-cAMP or okadaic acid resulted in ligand-independent transcriptional activation of the cPR. The surprising finding that cPR can be activated in the absence of hormone has been followed by numerous studies from other laboratories examining the effects of modulators of kinases and phosphatases on the activity of other steroid receptors. These studies have yielded mixed results: ligand-independent activation has been observed in some cases, but not in others. In order to determine whether the ligand-independent activation of cPR was restricted to a specific reporter and cell type and to better characterize this phenomenon, the studies in this report were undertaken. Using both the original reporter, PREtkCAT, and a simpler reporter, GRE2E1bCAT, we found that ligand-independent activation of the cPR can be induced in both CV1 and HeLa cells. The magnitude of the response and the response of the reporter alone differed in the two cell types. Further analysis of the activation of cPR by inhibitors of protein phosphatases showed that inhibition of phosphatase 1 rather than phosphatase 2A was necessary for activation of cPR. Finally, treatment with vanadate, an inhibitor of phosphotyrosine phosphatases, or epidermal growth factor resulted in activation of cPR. These studies suggest that signals transduced through multiple signaling pathways can activate cPR.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1992

Evidence for interaction between v-Mos and a p34cdc2 isoform, p35cdk.

The c-mos gene product (c-Mos) encodes a serine/threonine kinase required for activation of pre-MPF (maturation-promoting factor) to MPF in oocytes undergoing meiosis and also for stabilization of MPF leading to metaphase arrest in unfertilized eggs. In order to determine whether the v-mos gene product (v-Mos) causes neoplastic transformation via interaction with cell cycle control elements, we have searched for proteins that interact with v-Mos. Extracts of NIH3T3 cells transformed by v-Mos encoded by Moloney murine sarcoma virus (Mo-MuSV) were examined by gel filtration, by immunoprecipitation with antibodies to a conserved region of p34cdc2, and by binding to beads that contain cross-linked p13suc1, a protein known to bind p34cdc2. Gel filtration detected a 500-kDa complex that contained v-Mos and a p34cdc2 isoform, termed p35cdk. The 500-kDa macromolecular complex also exhibited histone H1 phosphorylation activity, consistent with the presence of a cdc2 isoform. The identity of p35cdk is based on its recognition by anti-cdc2 PSTAIR but not by anti-cdc2 C-terminal antibodies, which detect authentic p34cdc2. Structures containing v-Mos and p35cdk were also detected by experiments involving co-immunoprecipitation of v-Mos with anti-cdc2 PSTAIR antibodies. Furthermore, both v-Mos and the p35cdk co-precipitated with p13suc1-Sepharose beads. Our findings raise the possibility of a v-Mos-p35cdk regulatory interaction in cells transformed by Mo-MuSV.

3T3 Cells↗
PubMed1992

The physical interactions between p37env-mos and tubulin structures.

The c-mos protein has been reported to be complexed with tubulin and to co-localize with microtubules in unfertilized Xenopus eggs as well as in NIH3T3 cells transformed by the Xenopus c-mos gene. We performed experiments to determine whether the viral mos protein, p37v-mos, also associates with tubulin. Both mouse c-mos and v-mos proteins synthesized in vitro co-polymerized with tubulin. Upon incubation at 37 degrees C, essentially all of the mos protein (both viral and cellular) co-polymerized with tubulin, while more than 50% of the tubulin remained in the depolymerized state. The mos-tubulin interaction was specific, as indicated by the insolubility of the v-mos protein following a second cycle of temperature-dependent depolymerization/polymerization. Beta-tubulin was shown to co-precipitate with p37v-mos and to be phosphorylated by the mos kinase in vitro. Although both v-mos and c-mos proteins co-polymerize with tubulin, p37v-mos behaved differently from p39c-mos on gel filtration columns under conditions that favor disassembly of microtubules. Like Xenopus c-mos, the bulk of the mouse c-mos protein synthesized in vitro appeared in structures that fractionate at about 500 kDa. In contrast to c-mos, the majority of the v-mos protein, either isolated from stably transformed NIH3T3 cells or synthesized in vitro, eluted in the 100 kDa fraction, co-fractionating with tubulin dimers. Therefore, the v-mos protein appears to have a higher affinity for unpolymerized tubulin than c-mos, under conditions that favor disassembly of microtubules.

3T3 Cells↗