Expression of cellular repressor of E1A-stimulated genes in vascular smooth muscle cells of different phenotypes

Abstract

The phenotypic modulation of vascular smooth muscle cells (VSMC) plays a central role in the pathogenesis of arteriosclerosis. The purpose of this study was to investigate the expression of the cellular repressor of E1A-activated genes (CREG) at the transcriptional and protein level in human internal thoracic artery smooth muscle cells (HITASY), which express different patterns of differentiation markers after serum withdrawal. After cloning and recombining the CREG vector, the antiserum against the CREG protein was produced from the rabbits immunized by the purification CREG protein. The specificity of purified polyclonal antibody was detected by Western blot assay. The DNA synthesis of HITASY cultured in serum-free and serum-supplemented medium was measured by the [(3)H]-thymidine incorporation. Western blot analysis detected the expression of smooth muscle-specific markers (smooth muscle alpha-actin, calponin). The localization of CREG in cells was examined with immunohistochemistry staining and expression of CREG mRNA and protein were analyzed by RT-PCR and Western blot in HITASY after serum withdrawal. The high specificity of polyclonal antibody against CREG obtained from rabbits was confirmed by Western blot assay. In response to serum withdrawal, cultured HITASY cells exhibited phenotypic conversion from synthetic into contractile one as evidenced by the data of [(3)H]-thymidine incorporation and Western blot. The DNA synthesis of HITASY precipitously dropped to background levels after serum withdrawal and nearly restored after reintroduction of serum to culture medium 2 days later. Western blot revealed a reversible upregulation of smooth muscle alpha-actin and calponin in HITASY after serum deprivation. Moreover, serum withdrawal also induced a prominent increase of CREG mRNA and protein expression which reached a peak on 3 days and decreased gradually on 5 approximately 7 days after serum withdrawal. Immunohistochemistry stain indicated the CREG protein mainly localizes in a perinuclear pattern in HITASY cells. Those data provide evidence that the coordinated changes in CREG gene and protein expression as well as smooth muscle-specific markers may take place in connection with the process of phenotypic modulation of VSMC in vitro.