Regulation of Agonist- and Antagonist-Mediated Activation of Human Progesterone Receptors by Phosphorylation.
Annual rept. 1 Jul 94-30 Jun 95,
BAYLOR COLL OF MEDICINE HOUSTON TX
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Human progesterone receptor hPR in T47D breast cancer cells is phosphorylated upon hormonal treatment. The phosphorylation includes a rapid 32P incorporation into hPR followed by a characteristic decrease of hPR mobility on SDS gel electrophoresis SDS-PAGE without further significant increase of phosphorylation. Current studies have shown that hPR can be activated by the antiprogestin RU486 in the presence of 8-Br cAMP. This switch of RU486 antagonist activity to agonist activity is thought to related to the phosphorylation of hPR or factors associating with hPR. To understand the role of phosphorylation in hPR activity and the switch, I sought to locate the phosphorylation sites in hPR. Thus far, I have identified eight phosphorylation sites including three hormone-dependent phosphorylation sites, Ser102, Ser294 and Ser345 and five basal phosphorylation sites, Ser81, Ser162, Ser190, Ser294 and Ser548. Of these sites, Ser81, Ser102 and Ser162 are in the PR-B specific region. Interestingly, phosphorylation of Ser345 is required for the altered mobility on SDS gel electrophoresis. In addition, I have found that PR-B but not PR-A is responsible for the switch. Finally, I have shown that mutation of Ser81, a OKII site, to Ala dramatically decreased the transcriptional activity of the receptor using a transient transcription assay.
- Medicine and Medical Research