Minisymposium XV. Transcriptional Regulation of Gene Expression in the Ovary
Chair(s): Davis, John,
Location: CCQ 2000A
(MS46) REGULATION OF TRANSFORMING GROWTH FACTOR-BETA1 (TGF) TRANSCRIPTION BY THE EARLY GROWTH RESPONSE FACTOR 1 (Egr1) TRANSCRIPTION FACTOR IN THE CORPUS LUTEUM (CL).
Hou, Xiaoying1, 2, Arvisais, Edward1, 2, Davis, John1, 2, 1 University of Nebraska Medical Center, Omaha, NE2 VA Medical Center, Omaha, NE
ABSTRACT- In mammals, including primates and humans, prostaglandin F2 (PGF2) is believed to be the trigger that induces the regression of the CL, whereby progesterone synthesis is inhibited, the luteal structure involutes, and the menstrual or estrus cycle resumes. However, the cellular and molecular mechanisms of PGF2-induced CL regression remain poorly understood. As it is well established that PGF2 activates the PKC/Raf/MEK/ERK signaling pathway, our objectives were to identify genes responsive to PGF2 and activators of this pathway. Our data demonstrate that the expression of Egr1 mRNA and protein is up-regulated in the CL during PGF2-induced luteolysis in vivo and in PGF2-treated luteal cells in vitro. Studies have shown that Egr1 protein can induce the activation of various proapoptotic proteins, suggesting that Egr1 may play a role in luteal regression. Our hypothesis is that Egr1 mediates the actions of PGF2 by inducing the expression of key proapoptotic proteins. Egr1 protein was elevated in nuclear extracts prepared from PGF2-treated cells, and nuclear extracts bound a GC-rich Egr1 consensus motif, indicating that the newly synthesized Egr1 transcription factor was functional. Using a variety of chemical and genetic approaches, the PKC/Raf/MEK/ERK pathway was identified as the proximal signaling event required for the induction of Egr1 in PGF2-treated cells. TGF is believed to exert proapoptotic effects in many cell types, and is expressed in the CL during regression. Treatment with PGF2 increased the expression of TGF mRNA and protein in bovine luteal cells. The effect of PGF2 on TGF expression was mimicked by PKC activators or overexpression of Egr1. The stimulatory effect of PGF2 on TGF mRNA and protein secretion was inhibited by blockade of PKC/Raf/MEK/ERK signaling and overexpression of NAB2, a co-repressor that binds to and inhibits Egr-1 transcriptional activity. Treatment of luteal cells with TGF reduced progesterone secretion and DNA synthesis, implicating TGF in luteal regression. These studies demonstrate that PGF2 via the PKC/Raf/MEK/ERK signaling pathway regulates the expression of Egr1 and TGF in the CL. We suggest that Egr1 may play a role the induction of genes that coordinate the regression of the CL.
KEY WORDS: the early growth response factor 1, Prostaglandin F 2 , Transforming growth factor 1, corpus luteum