Mechanical strain inhibits airway smooth muscle gene transcription via protein kinase C signaling

Mechanical strain affects airway myocyte phenotype, cytoskeletal architecture, proliferation, and contractile function. We hypothesized that (i) short-term mechanical strain modulates transcription of smooth muscle-specific gene promoters for SM22 and smooth muscle myosin heavy chain (smMHC); and (ii) strain-induced change is mediated by altered actin polymerization in association with activation of protein kinase C (PKC). Primary cultured canine tracheal myocytes were transiently transfected with luciferase reporter plasmids harboring a murine SM22, human smMHC, or artificial serum response factor (SRF)-specific gene promoter and then subjected to cyclic strain for 48 h. This strain protocol significantly reduced transcriptional activity of SM22 and smMHC promoters and an artificial SRF-dependent promoter by 55 5.9%, 57 +/- 6.4%, and 75 +/- 7.9%, respectively, with concomitant reduction in F/G actin ratio by 31 +/- 8%. PKC inhibitors, GF109203X or Go6976, significantly attenuated these affects. Similar to strain, strain-independent activation of PKC inhibited SM22, smMHC, and SRF-dependent promoter activity by 61 +/- 4%, 66 +/- 5%, and 28 +/- 15%, respectively, and reduced the F/G actin ratio by 30 +/- 5%. Gel shift assay revealed that PKC activation led to decreased binding of the required transcription factor, SRF, to CArG elements in the SM22 promoter. These data suggest a previously unknown role for PKC isoforms in mechanosensitive signaling in airway myocytes that is associated with coordinated regulation of actin cytoskeletal dynamics and smooth muscle-specific gene transcription.