Antibodies to the α(q) subfamily of guanine nucleotide-binding regulatory protein α subunit attenuate activation of phosphatidylinositol 4,5-bisphosphate hydrolysis by hormones

The subfamily of guanine nucleotide-binding regulatory (G proteins) designated G(q) has been shown to regulate the activity of phospholipase C by reconstitution. However, the role of these proteins in hormonal regulation of this activity has not been demonstrated: Two antisera were used in attempts to interrupt this pathway. Antiserum W082, developed against a peptide representing an internal sequence in α(q), was specific for α(q) by immunoblots but did not recognize the native protein. Antiserum X384 was developed against a peptide representing the 12 amino acids of the common carboxyl termini of α(q) and α₁₁. It had a broader specificity for this subfamily of G protein α subunits and recognized the native proteins. Antiserum X384 specifically immunoprecipitated α(q) and its homologs from purified preparations and detergent extracts of membranes. Affinity-purified antibodies attenuated stimulation of phosphatidylinositide 4,5-bisphosphate hydrolysis by bradykinin, angiotensin, and histamine in membranes derived from NG108-15 cells, rat liver, and 1321N1 cells, respectively. Activation of the phospholipase C activity by guanosine 5'-3-O-(thio)triphosphate alone was also inhibited. Inclusion of the peptide to which the antisera were raised blocked the effect of the antibody. In contrast, affinity-purified W082, which did not recognize native proteins, did not alter regulation of phospholipase C. This indicates that the G(q) family of signaling proteins can couple to several receptors and is responsible for the hormonal regulation of phospholipase C in these diverse systems. The further generality of this regulatory pathway remains to be established.