Abstract 804: A Novel Vascular Smooth Muscle Cell Specific Histone Acetyl-transferase Regulates Vascular Smooth Muscle Differentiation
The appearance of smooth muscle (SM) gene activity is important for the formation of the cardiovascular system during embryonic development. The expression of SM marker genes is transcriptionally controlled by serum response factor (SRF) interacting with multiple co-factors including myocardin, GATA factors and LIM-domain only factor CRP2. The histone acetyl-transferases (HAT) have been suggested to be recruited to the complexes and remodel the chromatin. We here report that a novel HAT, SM-HAT regulates expression of SM marker genes. The SM-HAT contains a carboxyl-terminal HAT domain which is sufficient for acetylating core histones in vitro. The staining of SM-HAT lacZ knock-in mouse embryos suggested that SM-HAT was expressed specifically in vascular smooth muscles in early embryonic development. Knocking-down of the endogenous SM-HAT in rat vascular SM cell-line A7r5 by siRNA reduced the endogenous expression level of SM genes SM22, calponin and SM-MHC, suggesting SM-HAT is indispensable for SM gene expression. Overexpression of SM-HAT alone in A7r5 cells can elevate the expression level of SM22 and SM-MHC. Luciferase reporter assays suggest the SM-HAT can synergistically activate SM markers with either SRF/CRP2/GATA6 or SRF/myocardin. The SM-HAT interacts with SRF, CRP2 and myocardin as shown by immunocoprecipitation and GST pull-down assays. The interaction domain of SM-HAT was mapped to the region adjacent to the amino-terminal of HAT domain. Using chromatin-immunoprecipitation (ChIP), the SM-HAT was found on the serum response elements (SREs) in the SM gene promoters. The overexpression of SM-HAT leaded to the hyperacetylation of histones in the promoter regions with SRE sites. In the summary the novel SMC specific HAT, SM-HAT interacts with multiple co-factors in the SRF transcription complex and is recruited to the SMC promoters. It increases the transcription activity of SMC marker genes by locally acetylating the histones.