Adenylyl cyclase inhibition and altered G protein subunit expression and ADP-ribosylation patterns in tissues and cells from Gi2 alpha-/-mice.
The inhibition of alpha i2-/- mouse cardiac isoproterenol-stimulated adenylyl cyclase (AC; EC 4.6.1.1) activity by carbachol and that of alpha i2-/- adipocyte AC by phenylisopropyladenosine (PIA), prostaglandin E2, and nicotinic acid were partially, but not completely, inhibited. While the inhibition of cardiac AC was affected in all alpha i2-/- animals tested, only 50% of the alpha i2-/- animals showed an impaired inhibition of adipocyte AC, indicative of a partial penetrance of this phenotype. In agreement with previous results, the data show that Gi2 mediates hormonal inhibition of AC and that Gi3 and/or Gi1 is capable of doing the same but with a lower efficacy. Disruption of the alpha i2 gene affected about equally the actions of all the receptors studied, indicating that none of them exhibits a striking specificity for one type of Gi over another and that receptors are likely to he selective rather than specific in their interaction with functionally homologous G proteins (e.g., Gi1, Gi2, Gi3). Western analysis of G protein subunit levels in simian virus 40-transformed primary embryonic fibroblasts from alpha i2+/+ and alpha i2-/- animals showed that alpha i2 accounts for about 50% of the immunopositive G protein alpha subunits and that loss of the alpha i2 is accompanied by a parallel reduction in G beta 35 and G beta 36 subunits and by a 30-50% increase in alpha i3. This suggests that G beta-gamma levels may be regulated passively through differential rates of turnover in their free vs. trimeric states. The existence of compensatory increase(s) in alpha i subunit expression raises the possibility that the lack of effect of a missing alpha i2 on AC inhibition in adipocytes of some alpha i2-/- animals may be the reflection of a more pronounced compensatory expression of alpha i3 and/or alpha i1.
Rudolph
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U
Department of Cell Biology, Baylor College of Medicine, Houston, TX 77030, USA.
Spicher
K
K
Birnbaumer
L
L
D000246:Adenosine Diphosphate Ribose / Q000378:metabolism*; D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D000273:Adipose Tissue / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D002461:Cell Line, Transformed; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000172:deficiency* / Q000235:genetics*; D015870:Gene Expression; D018390:Gene Targeting; D051379:Mice; D009206:Myocardium / Q000378:metabolism; D037342:Pertussis Toxin; D010641:Phenotype; D011487:Protein Conformation; D014018:Tissue Distribution; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D010566:Virulence Factors, Bordetella; D000246:Adenosine Diphosphate Ribose; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins