Abstract
The mechanisms that regulate smooth muscle development and differentiation are poorly understood. Although recent studies have suggested the possible role of a zinc finger transcription factor, GATA-6, in the differentiation of vascular smooth muscle cells (VSMCs), the downstream gene targeted by GATA-6 is unknown. The expression of smooth muscle-myosin heavy chain (Sm-MHC) provides a highly specific marker for the differentiated phenotype of VSMCs as well as the smooth muscle cell lineage. Here, we show that GATA-6 bound to a GATA-like motif (-810/-805) within the rat Sm-MHC promoter in a sequence-specific manner and activated this promoter through this site. In addition, we show that the transcriptional coactivator p300 associated with GATA-6 during the transcription of the Sm-MHC gene. A p300/GATA-6 complex in VSMCs was up-regulated by induction of the quiescent phenotype. A wild-type E1A, which interferes with endogenous p300, but not a mutant E1A defective for p300 binding, markedly down-regulated the expression of endogenous Sm-MHC in quiescent-phenotype VSMCs. These studies provide the first identification of a functionally important GATA-6 binding site within a smooth muscle-specific promoter and suggest a role for p300 in the maintenance of the differentiated phenotype in VSMCs as a coactivator of GATA-6.
Highlights
The intimal proliferation of vascular smooth muscle cells (VSMCs)1 is known to play an integral role in development of atherosclerotic disease and restenosis after angioplasty [1,2,3,4,5,6,7]
Recent studies have suggested the possible role of a zinc finger transcription factor, GATA-6, in the differentiation of vascular smooth muscle cells (VSMCs), the downstream gene targeted by GATA-6 is unknown
To determine whether the distal GATA-like motif (Ϫ810/Ϫ805) in the rat smooth muscle-myosin heavy chain (Sm-MHC) promoter can interact with GATA-6, Electrophoretic Mobility Shift Assays (EMSAs) were performed
Summary
The intimal proliferation of vascular smooth muscle cells (VSMCs) is known to play an integral role in development of atherosclerotic disease and restenosis after angioplasty [1,2,3,4,5,6,7]. Overexpression of GATA-6 in proliferating VSMCs induces cell cycle arrest [20] These data suggest that GATA-6 plays a role in the maintenance of the differentiated phenotype in VSMCs. the downstream smooth muscle-specific gene targeted by GATA-6 has yet to be identified. We reported that adenovirus E1A oncoprotein represses the GATA-5-dependent transactivation of a promoter derived from the cardiac-restricted atrial natriuretic factor gene. This repression was correlated with the interaction of E1A with p300, indicating that p300 participates in GATA-5dependent transactivation [21]. The interaction of p300 and GATA proteins and a possible role of GATA-6 in VSMC differentiation suggest the hypothesis that p300 mediates smooth muscle-specific gene expression. The SmMHC gene provides a potentially useful promoter for studying the regulation of the SMC differentiation state and the factors involved in specifying the proliferative or quiescent/differentiated SMC phenotype
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