Insulin-like growth factor-I-coupled mitogenic signaling in primary cultured human skeletal muscle cells and in C2C12 myoblasts. A central role of protein kinase Cdelta.
In this study, we have investigated the effects of insulin-like growth factor-I (IGF-I) on cellular responses of primary human skeletal muscle cells and mouse C2C12 myoblasts. In human muscle, IGF-I stimulated proliferation and fusion of the cells and the expression of the differentiation marker desmin. These effects were completely inhibited by Rottlerin, the inhibitor of the protein kinase C (PKC)delta, but were not affected by the inhibition of the mitogen-activated protein kinase (MAPK) or the phosphatidylinositide 3-kinase (PI-3K) pathways. Furthermore, IGF-I initiated the selective translocation of PKCdelta to the nucleus. In C2C12 myoblasts, the growth-promoting effects of IGF-I were abrogated by inhibition of PKCdelta, but not by the inhibition of the PI-3K system. However, in contrast to the human data, the MAPK inhibitor PD098059 partially (yet significantly) also inhibited the action of IGF-I and, furthermore, IGF-I induced phosphorylation of the MAPK Erk-1/2. In addition, overexpression of constitutively active form of PKCdelta in C2C12 cells fully mimicked, whereas overexpression of kinase inactive mutant of the isoform prevented the action of IGF-I. Finally, the inhibition of PKCdelta suspended the IGF-I-induced phosphorylation of Erk-1/2 and, moreover, the inhibition of the MAPK pathway partially (yet significantly) inhibited the accelerated growth of C2C12 cells overexpressing PKCdelta. Taken together, these results demonstrate a novel, central and exclusive involvement of PKCdelta in mediating the action of IGF-I on human skeletal muscle cells, with an additional yet PKCdelta-dependent contribution of the MAPK pathway on C2C12 myoblasts.
Czifra
Gabriella
G
Department of Physiology, University of Debrecen, Medical and Health Science Center, Research Center for Molecular Medicine, Debrecen, Hungary.
Tóth
István Balázs
IB
Marincsák
Rita
R
Juhász
István
I
Kovács
Ilona
I
Acs
Péter
P
Kovács
László
L
Blumberg
Peter M
PM
Bíró
Tamás
T
D000818:Animals; D002454:Cell Differentiation; D002478:Cells, Cultured; D003893:Desmin / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008938:Mitosis / Q000502:physiology*; D018482:Muscle, Skeletal / Q000166:cytology*; D032446:Myoblasts / Q000166:cytology / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051745:Protein Kinase C-delta / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*
D003893:Desmin; D007527:Isoenzymes; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; D051745:Protein Kinase C-delta; D020928:Mitogen-Activated Protein Kinases