Mutant alpha-subunit of the G protein G12 activates proliferation and inhibits differentiation of 3T3-F442A preadipocytes.
We studied the G protein alpha-subunit Galpha12 in various tissues and cell lines. Significant amounts of Galpha12 were detected by immunoblots in liver, chromaffin cells, RINm5F cells, 3T3-F442A cells, and preadipocytes, but not in adipocytes, sperm, kidney, NB2A cells, or brain. To study the role of Galpha12 in adipose tissue differentiation, the preadipocyte cell line 3T3-F442A was transfected with wild-type Galpha12 or a constitutively activated mutant of Galpha12. Stable expression of the activated mutant of Galpha12 stimulated cell growth and inhibited preadipocyte differentiation. In contrast, wild-type Galpha12 overexpression inhibited preadipocyte differentiation, without any effect on cell proliferation. The role of Galpah12 on the Raf/MEK/mitogen-activating protein kinase (MAPK) cascade was studied. In confluent preadipocytes, expression of the activated mutant of Galpha12 induced an increase in B-Raf expression, but no change in MAPK activity. Differentiation was associated with a decrease in MAPK activity in control 3T3-F442A cells. Wild-type Galpha12 overexpression prevented the decrease in MAPK activity and induced MEK1, but not B-Raf, expression. Moreover, the activated mutant of Galpha12 induced an increase in MAPK activity and in the expression of both MEK1 and B-Raf. These data indicate that the activated mutant of Galpha12 stimulates the proliferation of 3T3-F442A preadipocytes, possibly through an increase in B-Raf expression, independently of the MEK/MAPK pathway, but prevents differentiation, probably through an increase in MEK1 expression and MAPK activity.
Denis-Henriot
D
D
Laboratoire de Biochimie de la Faculté de Médecine Paris-Ouest, INSERM CJF 94-02, Université René Descartes Paris V, France.
de Mazancourt
P
P
Morot
M
M
Giudicelli
Y
Y
D017667:Adipocytes / Q000166:cytology* / Q000378:metabolism / Q000502:physiology; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D002460:Cell Line / Q000166:cytology / Q000502:physiology; D019204:GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D009154:Mutation / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D013234:Stem Cells / Q000166:cytology* / Q000378:metabolism / Q000502:physiology; D014162:Transfection
D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019204:GTP-Binding Proteins