PKA implicated in the phosphorylation of Cx43 induced by stimulation with FSH in rat granulosa cells.
Connexin 43 (Cx43)-mediated gap junctional communication in granulosa cells is crucial for germ line development and postnatal folliculogenesis. We previously showed that follicle-stimulating hormone (FSH) promoted phosphorylation of Cx43 in rat primary granulosa cells. We further identified Ser365, Ser368, Ser369, and Ser373 in the carboxy-terminal tail as the major sites of phosphorylation by FSH, and found that the phosphorylation of these residues was essential for channel activity. In this study, we investigated the protein kinase(s) responsible for FSH-induced phosphorylation. H89, a cyclic AMP-dependent protein kinase (PKA) inhibitor, inhibited FSH-induced phosphorylation both in vivo and in vitro, whereas PD98059, a mitogen-activated protein kinase kinase (MEK) inhibitor, had little effect on the phosphorylation level. Ca2+-dependent protein kinase (PKC) appeared to negatively regulate phosphorylation. Phosphopeptide mapping with or without H89 treatment indicated that PKA could be responsible for phosphorylation of the four serine residues. In addition, the purified catalytic subunit of PKA could phosphorylate the recombinant C-terminal region of Cx43, but not the variant in which all four serine residues were substituted with alanine. These results suggest that FSH positively regulates Cx43-mediated channel formation and activity through phosphorylation of specific sites by PKA.
Graduate School of Biological Sciences, Nara Institute of Science and Technology, Japan. ke-yogo@bs.naist.jp
Keiichiro
K
Yogo
Takuya
T
Ogawa
Motofusa
M
Akiyama
Norihiro
N
Ishida-Kitagawa
Hiroshi
H
Sasada
Eimei
E
Sato
Tatsuo
T
Takeya
D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D018031:Connexin 43 / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000502:physiology*; D006107:Granulosa Cells / Q000378:metabolism*; D007473:Ion Channels / Q000096:biosynthesis; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012694:Serine / Q000378:metabolism
D018031:Connexin 43; D007473:Ion Channels; D012694:Serine; D005640:Follicle Stimulating Hormone; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C