Phosphorylation of the small heat shock-related protein, HSP20, in vascular smooth muscles is associated with changes in the macromolecular associations of HSP20

Cyclic nucleotide-dependent vasorelaxation is associated with increases in the phosphorylation of a small heat shock-related protein, HSP20, We hypoth esized that phosphorylation of HSP20 in vascular smooth muscles is associat ed with alterations in the macromolecular associations of HSP20, Treatment of bovine carotid artery smooth muscles with the phosphodiesterase inhibito r, 3-isobutyl-1-methylxanthine, and the adenylate cyclase activator, forsko lin, led to increases in the phosphorylation of HSP20 and dissociation of m acromolecular aggregates of HSP20, However, 3-isobutyl-1-methylxanthine and forskolin treatment of a muscle that is uniquely refractory to cyclic nucl eotide-dependent vasorelaxation, human umbilical artery smooth muscle, did not result in increases in the phosphorylation of HSP20 or to dissociation of macromolecular aggregates. HSP20 can be phosphorylated in vitro by the c atalytic subunit of cAMP-dependent protein kinase (PKA) in both carotid and umbilical arteries and this phosphorylation of HSP20 is associated with di ssociation of macromolecular aggregates of HSP20. Activation of cyclic nucl eotide-dependent signaling pathways does not lead to changes in the macromo lecular associations of another small heat shock protein, HSP27. interestin gly, the myosin light chains (MLC20) are in similar fractions as the HSP20, and phosphorylation of HSP20 is associated with changes in the macromolecu lar associations of MLC20. These data suggest that increases in the phospho rylation of HSP20 are associated with changes in the macromolecular associa tions of HSP20. HSP20 may regulate vasorelaxation through a direct interact ion with specific contractile regulatory proteins.