Hyperplasia suppressor gene associates with smooth muscle alpha-actin and is involved in the redifferentiation of vascular smooth muscle cells.

Vascular smooth muscle cell (VSMC) differentiation and phenotypic modulation are characterized by changes in gene expression for smooth muscle (SM) marker contractile proteins such as SM alpha-actin and SM22alpha. Hyperplasia suppressor gene (HSG) is a potent VSMC proliferation-inhibiting factor; however, it is not known if HSG is involved in the redifferentiation of VSMCs. Here, the redifferentiation of the dedifferentiated VSMCs was induced by serum withdrawal or all-trans retinoic acid (atRA), HSG gene expression and its role in VSMC phenotypic modulation were studied by reverse transcription - polymerase chain reaction, Western blotting, and cell migration assay. The results indicated that HSG gene expression increased significantly during VSMC redifferentiation induced by serum deprivation or atRA and peaked at 24 h, then was maintained at higher levels. Meanwhile, SM marker contractile proteins SM alpha-actin and SM22alpha were increased by more than 2-fold. Coimmunoprecipitation and immunofluorescent experiments revealed that anti-HSG antibody could precipitate SM alpha-actin, and HSG and SM alpha-actin colocalized within the cytoplasm of differentiated VSMCs. Migration activity of VSMCs was dramatically suppressed after cells were transfected with HSG expression plasmids. These findings suggested that HSG is associated with SM alpha-actin in VSMC cytoplasm, and is involved in VSMC differentiation and migration.