Cell cycle-dependent coupling of the vasopressin V(1a) receptor to different G proteins

Abstract

Arginine vasopressin (AVP) regulates biological processes by binding to G protein-coupled receptors. In Swiss 3T3 fibroblasts, expressing the V(1a) subtype of vasopressin receptors, AVP mobilizes calcium from intracellular stores. In proliferating cells, the AVP-induced increase in intracellular calcium concentration ([Ca2+](i)) was mediated by G proteins of the G(q) family, which are insensitive to pertussis toxin (PTX) pretreatment of the cells. In quiescent cells, the AVP-induced increase in [Ca2+](i) was partially PTX-sensitive, suggesting an involvement of G(i) proteins. We confirmed this by photoaffinity labeling of G proteins in Swiss 3T3 cell membranes activated by AVP. In Swiss 3T3 cells arrested in the G0/G1 phase of the cell cycle, the AVP-induced increase in [Ca2+](i) was also partially PTX-sensitive but was PTX-insensitive in cells arrested in other phases of the cell cycles. The blocking effect of PTX pretreatment in G0/G1 cells was mimicked by microinjection of antisense oligo-nucleotides suppressing the expression of the Gα(i3) subunits. These results were confirmed by microinjection of antibodies directed against the C terminus of G protein α-subunits. The data presented indicate that in Swiss 3T3 fibroblasts synchronized in the G0/G1 phase of the cell cycle the V(1a) receptor couples to G(q/11) and G(i3) to activate the phospholipase C-β, leading to release of intracellular calcium.