Rapid activation of MAP kinase by estrogen in the bone cell line

We examined the effect of estrogen on mitogen-activated protein kinase (MAPK) in osteoblastic cells. Rat ROS 17/2.8 cells were exposed to 17 beta-estradiol (E-2) and MAPK activity in the cells was measured by an in vitro phosphorylation assay. E-2 treatment caused a rapid and transient MAPK activation within 5 min. Insulin-like growth factor-I, which acts via their membrane receptors, caused a similar effect, but it required 10 min to reach the maximum level. Western blot analyses with anti-MAPK and anti-phosphotyrosine antibodies demonstrated that the E-2 activation of MAPK was accompanied by phosphorylation of the enzyme. The concentration range (10 nM-1 pM) of E-2 needed for this MAPK activation was less than that (1 mu M-0.1 nM) needed for the transcriptional activation via the nuclear estrogen receptor (ER). These data provide the first evidence of MAPK activation by E-2 through phosphorylation, which may be mediated through a putative plasma membrane receptor in the cultured bone cells. (C) 1997 Academic Press.