Smooth muscle 22 alpha maintains the differentiated phenotype of vascular smooth muscle cells by inducing filamentous actin bundling.
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.
Han
Mei
M
Department of Biochemistry and Molecular Biology, Institute of Basic Medicine, Hebei Medical University, No. 361, Zhongshan East Road, Shijiazhuang 050017, China.
Dong
Li-Hua
LH
Zheng
Bin
B
Shi
Jian-Hong
JH
Wen
Jin-Kun
JK
Cheng
Yunhui
Y
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
D000199:Actins; D016895:Culture Media, Serum-Free; D008840:Microfilament Proteins; D009124:Muscle Proteins; D011993:Recombinant Fusion Proteins; C498862:Acta2 protein, rat; C051615:transgelin