β-arrestins regulate gonadotropin receptor-mediated cell proliferation and apoptosis by controlling different FSHR or LHCGR intracellular signaling in the hGL5 cell line.
Hepatocyte growth factor (HGF) is a mesenchymal-derived paracrine factor that acts through a c-met receptor. The activated c-met receptor recruits various signal proteins. We used a steroidogenic human granulosa-like tumor cell line (KGN cells) to analyze the biological function of HGF in human ovary cells. First, we designed a method to analyze local production and action of HGF in the human ovary. Although c-met mRNA is expressed in KGN cells, granulosa lutein, theca, and ovarian stroma cells, we observed HGF mRNA only in theca and stroma cells. Adding HGF to the medium enhanced mitogenic activity in KGN cells. We next examined the activation of intracellular signal transduction molecules induced by HGF in KGN cells. Here, we showed that HGF activated the distinct phosphorylation of Raf-1, MEK1/2, and ERK1/2, but did not induce phosphorylation of Akt. HGF enhanced the phosphorylation of Elk-1 and c-Jun as nuclear transcription factors. U0126, a MEK1/2 inhibitor, completely abrogated the phosphorylation of ERK1/2 and the cell proliferation in response to HGF. In contrast, H-89, a protein kinase A inhibitor, further enhanced the HGF-induced phosphorylation of ERK1/2 and cell proliferation. In addition, we revealed that HGF suppressed progesterone synthesis in KGN cells. Adding HGF suppressed the forskolin-induced steroidogenic acute regulatory protein (StAR) expression, which is a key regulator in progesterone synthesis. Crosstalk signals between PKA and the mitogen-activated protein kinase (MAPK) pathway were mutually inhibitory. These results demonstrated for the first time that theca cell-derived HGF may be capable of stimulating the proliferation of granulosa cells and suppressing progesterone synthesis via an activating MAPK pathway.