Date of Award
Open Access Thesis
Medical Doctor (MD)
James H. Segars
Medicine, Biology, Obstetrics and gynecology
Background--Uterine leiomyomas, or fibroids, are prevalent tumors that are dependent on sex steroids for growth. Clinically, progesterone promotes fibroid growth and anti-progestins cause a durable reduction in fibroid size, yet the mechanisms underlying progesterone action are unclear. A-kinase anchoring protein 13 (AKAP-13, also known as AKAP-Brx) functions as a Rho-GEF and is over-expressed in fibroids. AKAP-Brx has been shown to activate estrogen and glucocorticoid receptors, and bind these receptors via a nuclear receptor-binding motif. However, it is not known whether AKAP-Brx also binds progesterone receptor or augments progesterone action.
Objective--The purpose of this study was to determine if AKAP-Brx affected the activity of progesterone receptor B (PR-B), the more active isoform of the nuclear progesterone receptors.
Design--Controlled laboratory research studies.
Results--AKAP-Brx more than doubled progesterone-dependent gene activation by PR-B in two cell lines, including Cos7 cells and immortalized fibroid cells, and for two hormone dependent promoters. On the contrary, silencing of AKAP-Brx via RNA interference reduced progesterone dependent gene activation of endogenous PR-B-controlled-genes in a dose-dependent manner. In vitro and ex vivo binding studies suggest that AKAP-Brx and PR-B interact directly. Inhibition of MEK reduced AKAP-Brx enhancement of PR-B activity, suggesting that AKAP-Brx may affect PR-B via a pathway involving p44/42 MAPK (ERK1/2) phosphorylation. Inhibition of p38 MAPK, on the other hand, did not affect PR-B activation by AKAP-Brx.
Conclusion--This is the first report that AKAP-Brx augments gene activation by PR-B in a ligand-dependent manner in various cell types, including fibroids. AKAP-Brx may bind directly to PR-B and enhance its activity via ERK1/2 phosphorylation. These data suggest that the increased expression of AKAP-Brx in fibroids could promote progesterone-mediated fibroid growth.
Jorge, Soledad, "The Rho-Gef Akap-Brx Is A Co-Activator Of Progesterone Receptor B In Uterine Leiomyoma Cells" (2013). Yale Medicine Thesis Digital Library. 1805.