['Smooth muscle 22 alpha (SM22 alpha) is not required for the development and basal homeostatic function of smooth muscle cells (SMCs). However, a recent study demonstrated that SM22 alpha plays a role in inhibiting the phenotypic modulation of vascular SMCs (VSMCs) from contractile to synthetic/proliferative cells. The present study investigated the mechanism underlying the SM22 alpha-mediated maintenance of the contractile phenotype of VSMCs.', 'The redifferentiation of synthetic SMCs was induced by serum deprivation for 48-72 h. The expression plasmids containing full-length cDNA of rat SM22 alpha and a vector expressing SM22 alpha antisense transcripts were constructed, respectively. Coimmunoprecipitation, cosedimentation assay and immunofluorescence analyses were used to detect the interaction of SM22 alpha with F-actin.', 'The results revealed that SM22 alpha directly interacted and colocalized with F-actin and thus participated in the organization of the actin cytoskeleton in differentiated VSMCs. SM22 alpha facilitated the assembly of actin filaments into bundles. The blockade of SM22 alpha expression by SM22 alpha antisense RNA led to the thinning and dispersion of actin filaments. Consequently, the ratio of F-actin to globular (G)-actin was reduced, and the cell contractility was lost.'] Does smooth muscle 22 alpha maintain the differentiated phenotype of vascular smooth muscle cells by inducing filamentous actin bundling?