Gata3 and Ezh2 are Inversely Modulated by Progesterone in the Murine Mammary Gland.

CENCIARINI M, ; IZZO F; MERCOGLIANO MF; AMASINO MF; DA ROS V; DI GIORGIO NP; CHERVO MF; DE MARTINO M; LUX-LANTOS VA; CORDO RUSSO R; ELIZALDE PV; PROIETTI CJ

Chicago

Congreso; 100th Annual Meeting of the Endocrine Society; 2018

Endocrine Society

The mammary epithelium is a dynamic, highly hormone-responsive tissue. Transcription factor GATA3 is a master regulator that drives mammary luminal epithelial cell differentiation, and loss of its expression or function is associated with aggressive breast cancer (BC) development. The epigenetic mark H3K27me3 also emerged as a key mediator of lineage specification and hormone responsiveness. EZH2, the methyl-transferase responsible for this histone modification, is often overexpressed in BC, where it is associated with a more aggressive disease. We have already reported that progestins downregulate GATA3 to promote BC growth, in part by transcriptional repression through EZH2 and H3K27me3. As progesterone (P4) is the hormone that drives ductal branching and proliferation of the epithelial cells, we hypothesized that this mechanism was also taking place in the mammary gland. To test this, ovariectomized BALB/c mice were inoculated s.c. with either a P4 (5 mg) or a vehicle pellet for 7 days, after which mammary glands were extracted and processed to obtain whole protein extracts, RNA extracts and FFPE tissue. Similar to our report in BC, we found by both immunoblot and RT-qPCR that P4 downregulates GATA3 in the murine mammary gland. Also, immunoblot and IHC showed that EZH2 levels are increased after P4 exposure, as well as H3K27me3 levels. We had already found that progestin-induced GATA3 downregulation promotes BC cell proliferation by Cyclin A2 upregulation. This was also observed by IHC in the mammary glands of P4-treated mice. In order to gain insight into the physiological regulation of GATA3 by P4 throughout the estrous cycle, we extracted mammary glands of BALB/c mice in each of the four different phases: diestrus, proestrus, estrus, and metestrus. P4 serum levels increased progressively from estrus to proestrus (p