Date of Award

January 2013

Document Type

Open Access Thesis

Degree Name

Medical Doctor (MD)

Department

Medicine

First Advisor

James H. Segars

Second Advisor

Joshua Johnson

Subject Area(s)

Medicine, Biology, Obstetrics and gynecology

Abstract

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.

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