Sex-specific response of rat costochondral cartilage growth plate chondrocytes to 17β-estradiol involves differential regulation of plasma membrane associated estrogen receptors.

Both male and female rat growth plate chondrocytes express estrogen receptors (ERs); however 17β-estradiol (E(2)) induces membrane responses leading to activation of phospholipase A(2) (PLA(2)), phospholipase C (PLC), prostaglandin E(2) (PGE(2)) production, protein kinase C (PKC), and ultimately mitogen protein kinase (MAPK) only in female cells. This study investigated if these sex-specific responses are due to differences in the actual ERs or in downstream signaling. Western blots and flow cytometry of costochondral cartilage resting zone chondrocytes (RCs) showed 2-3 times more ERα in plasma membranes (PMs) from female cells than male cells. Tunicamycin blocked E(2)-dependent ER-translocation to the PM, indicating palmitoylation was required. Co-immunoprecipitation showed E(2) induced complex formation between ER isoforms only in female RCs. To examine if the lack of response on PKC and PGE(2) in males is due to differences in signaling, we examined involvement of ERs and the role of PLC and PLA(2). Selective ERα (propylpyrazole triol, PPT) and ERβ (diarylproprionitrile, DPN) agonists activated PKC in female RCs only. The PLC inhibitor, U73122 blocked E(2)'s effect on PKC and the cytosolic PLA(2) inhibitor, AACOCF3 inhibited the effect on PGE(2) in female RCs, confirming involvement of PLC and PLA(2) in the mechanism. The PLC activator, m-3M3FβS activated PKC and PLAA peptide increased PGE(2) levels in male and female RCs, showing that the signaling pathways are present. These data indicate that differences in membrane ER amount, localization, translocation and interaction are responsible for the sexual dimorphic response to E(2).