Protein kinase Ctheta expression is increased upon differentiation of human skeletal muscle cells: dysregulation in type 2 diabetic patients and a possible role for protein kinase Ctheta in insulin-stimulated glycogen synthase activity.
Protein kinase C (PKCtheta) is a key enzyme in regulating a variety of cellular functions, including growth and differentiation. PKCtheta is the most abundant PKC isoform expressed in skeletal muscle; however, its role in differentiation and metabolism is not clear. We examined the effect of muscle cell differentiation on PKCtheta expression in human skeletal muscle cells from normal and type 2 diabetic subjects. Low levels of PKCtheta messenger RNA (mRNA) and protein were detected in human myoblasts from both types of subjects. Upon differentiation into myotubes, PKCtheta mRNA and protein were increased 12-fold in myotubes from normal subjects. In human skeletal muscle cells obtained from type 2 diabetic subjects, increases in PKCtheta mRNA and protein were not observed upon differentiation into myotubes although expression of other markers of differentiation and fusion increased. Cells from type 2 diabetic subjects also exhibited decreased insulin-stimulated glycogen synthase activity. To determine whether the up-regulation of PKCtheta was important for the metabolic actions of insulin, PKCtheta was overexpressed in L6 rat skeletal muscle cells. Increased expression of PKCtheta occurred with differentiation of skeletal muscle myoblasts to myotubes. Glycogen synthase activity was further increased in L6 myotubes stably transfected with the complementary DNA for PKCtheta. The decreased expression of PKCtheta found in cells from type 2 diabetic subjects may be linked to insulin resistance and decreased glycogen synthase activity.
Department of Biochemistry and Molecular Biology, University of South Florida College of Medicine, Tampa 33612, USA.
C E
CE
Chalfant
T P
TP
Ciaraldi
J E
JE
Watson
S
S
Nikoulina
R R
RR
Henry
D R
DR
Cooper
D000328:Adult; D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D003847:Deoxyglucose / Q000378:metabolism; D003924:Diabetes Mellitus, Type 2 / Q000201:enzymology* / Q000473:pathology; D015870:Gene Expression; D006006:Glycogen Synthase / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D007527:Isoenzymes / Q000235:genetics*; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000201:enzymology / Q000473:pathology*; D011493:Protein Kinase C / Q000032:analysis / Q000235:genetics* / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D014162:Transfection
D007328:Insulin; D007527:Isoenzymes; D012333:RNA, Messenger; D003847:Deoxyglucose; D006006:Glycogen Synthase; D011493:Protein Kinase C