Decreased 8N3-[gamma-32P]GTP photolabeling of Gs alpha in tumorigenic lung epithelial cell lines: association with decreased hormone responsiveness and loss of contact-inhibited growth.
The 45-kDa alpha subunit of the signal transducing Gs protein complex, which stimulates receptor-coupled adenylate cyclase, incorporated less of the photoaffinity probe, 8N3-[gamma-32P]GTP, in extracts from tumorigenic cell lines in comparison with nontumorigenic cell lines derived from mouse lung epithelium. Immunoblotting experiments using anti-Gs alpha antibodies demonstrated that tumor cells do not have a decreased amount of Gs alpha and photolabeling of tumor cell Gs alpha increased when the rate of nucleotide exchange was promoted. Therefore, tumor cell Gs alpha function may be altered. Consistent with this hypothesis is the observation that the tumor cells exhibited decreased responsiveness to the beta-adrenergic agonist, isoproterenol. Gs alpha photolabeling in growing nontumorigenic cells was reduced to a level resembling that observed in tumor cells, but photolabeling increased when cells became contact-inhibited. This increase in 8N3-[gamma-32P]GTP incorporation into Gs alpha by normal cells at confluence was not seen in the tumorigenic cells. Since Gs alpha photolabeling was inversely proportional to the percentage of [3H]thymidine-labeled nuclei at confluence, we suggest that the altered Gs alpha in tumor cells is involved in the loss of cell growth regulation.
Droms
K A
KA
Molecular and Environmental Toxicology Program, School of Pharmacy, University of Colorado, Boulder 80309.
Haley
B E
BE
Smith
G J
GJ
Malkinson
A M
AM
D000345:Affinity Labels / Q000378:metabolism*; D000818:Animals; D001345:Autoradiography; D001386:Azides / Q000378:metabolism*; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D004848:Epithelium; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives* / Q000378:metabolism; D008168:Lung; D046911:Macromolecular Substances; D051379:Mice; D008970:Molecular Weight; D010761:Phosphorus Radioisotopes; D015398:Signal Transduction
C021961:8-azidoguanosine triphosphate; D000345:Affinity Labels; D001386:Azides; D046911:Macromolecular Substances; D010761:Phosphorus Radioisotopes; D006160:Guanosine Triphosphate; D000242:Cyclic AMP; D019204:GTP-Binding Proteins