Regulation of G-proteins in differentiation. Altered ratio of alpha- to beta-subunits in 3T3-L1 cells.
The complexion of the adenylate cyclase system and in particular, the regulation of G-proteins was examined in 3T3-L1 cells during differentiation from a fibroblast-like to an adipocyte-like phenotype. Gs alpha (the identified regulatory component of hormone-sensitive adenylate cyclase that mediates stimulation), measured by cholera toxin-catalyzed ADP-ribosylation, increased by approximately 6-fold from day 0 to day 8. Gs alpha, measured by functional reconstitution, increased in specific activity by approximately 3-fold from day 0 to day 8. Both Gi alpha (the G-protein with alpha-subunit Mr 40,000-41,000 whose function is in part the mediation of inhibition of adenylate cyclase) and Go alpha (the highly abundant G-protein first isolated from bovine brain whose effector system remains to be established) measured by pertussis toxin-catalyzed ADP-ribosylation increased by approximately 4-fold over this same period. 3T3-L1 cells possess beta-subunits of G-proteins displaying Mr = 36,000 (beta 36) and Mr = 35,000 (beta 35). The increase in the beta 35 as well as beta 36 subunits was approximately 2-fold. Using quantitative immunoblotting techniques and specific antisera, the total amount of beta-subunits was determined to be 150 as compared to 70 pmol/mg of membrane protein, while the amount of Go alpha was 40 and 10 pmol/mg of membrane protein in adipocytes and fibroblasts, respectively. Since Go alpha is the most abundant G-protein alpha-subunit observed to date in both phenotypes, the overall ratio of beta- to alpha-subunits of G-proteins appears to decrease from approximately 4.7 in fibroblasts to 2.5 in adipocytes. These data suggest that in differentiation not only is the complexion of G-proteins altered but more importantly, the relative amounts of alpha- to beta-subunits are regulated.
D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D037361:Adenylate Cyclase Toxin; D000262:Adenylyl Cyclases / Q000378:metabolism; D000273:Adipose Tissue / Q000166:cytology; D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002772:Cholera Toxin / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D007118:Immunoassay; D008970:Molecular Weight; D037342:Pertussis Toxin; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D010566:Virulence Factors, Bordetella; D000246:Adenosine Diphosphate Ribose; D002772:Cholera Toxin; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases