title: Smooth muscle 22 alpha maintains the differentiated phenotype of vascular smooth muscle cells by inducing filamentous actin bundling.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  The SM22 alpha-induced F-actin bundling enhances the contractility and mobility of VSMCs, and the activity of SM22 alpha is necessary for maintaining the differentiated phenotype of VSMCs.
authors.affiliation: Department of Biochemistry and Molecular Biology, Institute of Basic Medicine, Hebei Medical University, No. 361, Zhongshan East Road, Shijiazhuang 050017, China.
authors.forename: Mei
authors.initials: M
authors.lastname: Han
authors.forename: Li-Hua
authors.initials: LH
authors.lastname: Dong
authors.forename: Bin
authors.initials: B
authors.lastname: Zheng
authors.forename: Jian-Hong
authors.initials: JH
authors.lastname: Shi
authors.forename: Jin-Kun
authors.initials: JK
authors.lastname: Wen
authors.forename: Yunhui
authors.initials: Y
authors.lastname: Cheng
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D001013:Aorta, Thoracic / Q000166:cytology / Q000378:metabolism; D015153:Blotting, Western; D018929:Cell Culture Techniques; D002454:Cell Differentiation; D002465:Cell Movement / Q000502:physiology; D002478:Cells, Cultured; D016895:Culture Media, Serum-Free; D004591:Electrophoresis, Polyacrylamide Gel; D047468:Immunoprecipitation; D008297:Male; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D009119:Muscle Contraction / Q000502:physiology; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000378:metabolism; D010641:Phenotype; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000378:metabolism
chemical_list: D000199:Actins; D016895:Culture Media, Serum-Free; D008840:Microfilament Proteins; D009124:Muscle Proteins; D011993:Recombinant Fusion Proteins; C498862:Acta2 protein, rat; C051615:transgelin