Epidermal growth factor induces c-fos and c-jun mRNA via Raf-1/MEK1/ERK-dependent and -independent pathways in bovine luteal cells.
Epidermal growth factor (EGF) modulates the actions of gonadotropins in the corpus luteum. The membrane-associated EGF receptors undergo rapid tyrosine phosphorylation and internalization upon ligand binding in ovarian cells, including luteal cells. However, little is known about the post-receptor signaling events induced by EGF that lead to the transcriptional regulation of EGF-responsive genes in the ovary. The present study was designed to examine in bovine luteal cells (1) activation of the extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) signaling cascade (Raf/MEK/ERK) by EGF; (2) mRNA expression of AP-1 transcription factors, i.e. c-fos and c-jun, in response to EGF; and (3) the role of ERK in EGF-induced expression of c-fos and c-jun mRNA. Raf-1 and B-Raf, but not A-Raf, were activated by EGF (10 ng/ml) and the pharmacological protein kinase C (PKC) activator phorbol myristate acetate (PMA, 20 nM). Activation of Raf resulted in the phosphorylation and activation of MAPK kinase (MEK1) which subsequently activated ERKs. Treatment with EGF-induced the phosphorylation of both ERK2 and ERK1 in a time and concentration dependent manner. Additionally, activated ERK was found in the nucleus of the cells following treatment with EGF (10 ng/ml) and PMA (PMA, 20 nM) for 5 min. Depletion of PKC by chronic PMA treatment (2.5 microM, 24 h) only partially inhibited the stimulatory effects of EGF on Raf-1, ERK2 and ERK1. These data demonstrate that PKC-dependent and independent-mechanisms are involved in EGF activation of the Raf/MEK/ERK signaling cascade in bovine luteal cells. EGF rapidly and transiently stimulated the expression of c-fos and c-jun mRNA in bovine luteal cells. Maximal induction of c-fos and c-jun mRNA by EGF occurred within 30 min of treatment with 10 ng/ml EGF. Treatment with the MEK1 inhibitor PD098059 (50 microM) abolished EGF-induced ERK activation. However, blocking EGF-induced ERK activation by pretreatment with PD098059 only partially attenuated EGF-induced c-fos and c-jun mRNA expression. Thus, additional pathways are implicated in the regulation of c-fos and c-jun mRNA expression by EGF in bovine luteal cells.
Chen
Dong-bao
DB
The Women's Research Institute, Department of Obstetrics and Gynecology, University of Kansas School of Medicine-Wichita, 1010 North Kansas, Wichita 67214, USA. dochen@ucsd.edu
Davis
John S
JS
D000818:Animals; D002417:Cattle; D002467:Cell Nucleus / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D005260:Female; D008184:Luteal Cells / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism*; D048369:MAP Kinase Kinase 1; D020935:MAP Kinase Signaling System; D019950:Mitogen-Activated Protein Kinase 1 / Q000032:analysis / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000032:analysis / Q000378:metabolism; D011493:Protein Kinase C / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D048491:Proto-Oncogene Proteins A-raf; D048493:Proto-Oncogene Proteins B-raf; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis* / Q000235:genetics; D016755:Proto-Oncogene Proteins c-jun / Q000096:biosynthesis* / Q000235:genetics; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis
D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D004815:Epidermal Growth Factor; D017346:Protein Serine-Threonine Kinases; D048491:Proto-Oncogene Proteins A-raf; D048493:Proto-Oncogene Proteins B-raf; D019908:Proto-Oncogene Proteins c-raf; D011493:Protein Kinase C; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases