Protein kinase C isoforms in human airway smooth muscle cells: activation of PKC-zeta during proliferation.

Protein kinase C (PKC) is implicated in the regulation of smooth muscle contractility and growth. We have previously described the pattern of isoform expression of PKC in canine airway smooth muscle. This study identified the isoforms present in human cultured airway smooth muscle cells and also addressed the question of whether mitogenesis in these cells is associated with changes in a specific isoform, PKC-zeta. Western blot analysis revealed the presence of PKC-alpha, -betaI, and -betaII of the conventional group; PKC-delta, -theta, -epsilon, and -eta of the novel group; and PKC-zeta, -mu, and -iota of the atypical group. There was a significant increase in density of the Western blot for PKC-zeta in cells proliferating in response to 10% fetal bovine serum (FBS) to 372 +/- 115% of control values (P < 0.05; n = 3 patients) in the cytosolic fraction. Platelet-derived growth factor (PDGF) produced increases in PKC-zeta in both the cytosolic and membrane fractions to 210 +/- 49 and 443 +/- 227%, respectively, of control values (P < 0.05; n = 4 patients). There was no change in expression of PKC-alpha, -betaI, -betaII, -theta, -epsilon, -eta, -delta, or -iota in response to the same stimuli. PGE2 (1 microM) added to the cells 30 min before PDGF reduced incorporation of [3H]thymidine from 5,580 +/- 633 (SE) to 3, 980 +/- 126 dpm (P < 0.05; n = 3 patients) and, in addition, reduced expression of PKC-zeta in the membrane fraction as determined by Western blotting from 266 +/- 66 to 110 +/- 4% of control values (P < 0.05; n = 3 patients). PKC-zeta activity in stimulated cells (10% FBS), as assessed by immunoprecipitation and phosphorylation of glycogen synthase peptide, was approximately 3-fold greater than that in unstimulated cells, and the amount of PKC-zeta protein correlated with isoenzyme activity (r2 = 0.91; P < 0.02; n = 4 patients). In conclusion, this study 1) provides the first description of which isoforms of PKC are present in human cultured airway smooth muscle cells and 2) shows that proliferation of these cells is associated with upregulation of PKC-zeta. Whether activation of PKC-zeta is a primary or secondary event in airway smooth muscle cell proliferation remains to be determined.