HSP27 in signal transduction and association with contractile proteins in smooth muscle cells

Sustained smooth muscle contraction is mediated by protein kinase C (PKC) t hrough a signal transduction cascade leading to contraction. Heat-shock pro tein 27 (HSP27) appears to be the link between these two major events, i.e. , signal transduction and sustained smooth muscle contraction. We have inve stigated the involvement of HSP27 in signal transduction and HSP27 associat ion with contractile proteins (e.g., actin, myosin, tropomyosin, and caldes mon) resulting in sustained smooth muscle contraction. We have carried out confocal microscopy to investigate the cellular reorganization and colocali zation of proteins and immunoprecipitation of HSP27 with actin, myosin, tro pomyosin, and caldesmon as detected by sequential immunoblotting. Our resul ts indicate that 1) translocation of Raf-1 to the membrane when stimulated with ceramide is inhibited by vasoactive intestinal peptide (VIP), a relaxa nt neuropeptide; 2) PKC-alpha and mitogen-activated protein kinase transloc ate and colocalize on the membrane in response to ceramide, and PKC-alpha t ranslocation is inhibited by VIP; 3) HSP27 colocalizes with actin when cont raction occurs; and 4) HSP27 immunoprecipitates with actin and with the con tractile proteins myosin, tropomyosin, and caldesmon. We propose a model in which HSP27 is involved in sustained smooth muscle contraction and modulat es the interaction of actin, myosin, tropomyosin, and caldesmon.