Submitted on March 2, 2009
Revised on May 4, 2009
Accepted on May 21, 2009
Epidermal Growth Factor Receptor cross-talks with ligand occupied Estrogen Receptor 
to modulate both lactotroph proliferation and prolactin gene expression
Shenglin Chen1, Madhavi Latha Yadav Bangaru1, Leighton Sneade2, Joseph Dunckley2, Nira Ben-Jonathan2, and Sanjay Kansra1*
1 Medical College of Wisconsin
2 University of Cincinnati
* To whom correspondence should be addressed. E-mail: skansra{at}mcw.edu.
Both estrogen (E2) and epidermal growth factor (EGF) regulate lactotrophs, and we recently demonstrated that EGF phosphorylates S118 on ER
, and requires ER to stimulate PRL release. However, the interactions between ligand occupied ER and activated ErbB1, and its impact on lactotroph function is unknown. Using rat GH3 lactotrophs we found that both E2 and EGF independently stimulated proliferation and PRL gene expression. Further, their combination resulted in an enhanced stimulatory effect on both cell proliferation and PRL gene expression. Inhibitors of ER as well as ErbB1 blocked the combined effects of E2 and EGF. Pretreatment with UO126 abolished the combined effects demonstrating Erk1/2 requirement. Although bi-directionality in ER-ErbB1 cross-talk is a well accepted paradigm, interestingly in lactotrophs, ErbB1 kinase inhibitor failed to block the effect of E2 on proliferation and stimulation of PRL gene expression, suggesting that ER does not require ErbB1 to mediate its effects. Further, E2 did not affect the ability of EGF to induce c-fos expression or modulate AP-1 activity. However, both E2 and EGF combine to enhance S118 phosphorylation of ER, leading to enhanced E2 mediated ERE transactivation. Taken together, our results suggest that in lactotrophs activated ErbB1 phosphorylates ER to enhance E2's stimulatory effect, thereby providing the molecular basis by which EGF amplifies E2's response.
