Regulatory mechanism in gene expression of regulatory proteins in cardiac and vascular smooth muscles

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Calponin is actin-, tropomyosin binding protein which we found in the smooth muscle cells. In this project we studied the localization of calponin in smooth muscle cell and the physiological function of calponin.(1) We obtained thin filaments which contained actin, tropomyosin, caldesmon and calponin in molar rations of 7 : 0.9 : 0.6 : 0.7. Co-localization of actin and calponin was shown along stress fibers of smooth muscle cells from rat aorta.(2) We studied the function of calponin in vitro. Calponin inhibited the actinactivated myosin MgATPase activity in a dose-dependent manner. This inhibition was Ca-independent. The decrease in enzymatic activity of myosin was correlated with binding of calponin to actin-tropgmypsin filaments. Caldesmon showed a further inhibition of the calponin-induced inhibition of MgATPase activity of the thiophosphorylated myosin. Calponin-induced inhibition of the myosin MgATPase was reversed by the addition of calmodulin in the presence of Ca. These results suggest that calponin acts as an inhibitory component of smooth muscle thin filaments.(3) We performed cDNA cloning of SM22 from the chicken gizzard smooth muscle and rat aorta smooth muscle. Cloned cDNA encoding SM22 from the chicken gizzard smooth muscle had a total length of 1214bp and contained a single open reading frame which encodes 200 amino acids with a calculated molecular weight 22214. The predicted amino acid sequence was in complete agreement with the sequence determined by Pearlstone et al. who discovered the protein, except for two additional residues, isoleucine and serine at the C-terminus. The cDNA from rat aorta was 1186bp. in length and encoded 201 amino acids (Mr 22602). The predicted amino acid sequence showed an 85% Tdentity with the chicken gizzard SM22.