Zhao, Yuanyuan

Abstract Sprouting angiogenesis is a highly coordinately process controlled by vascular endothelial growth factor receptor (VEGFR)‐Notch signaling. Here we investigated whether Tripartite motif‐containing 28 (TRIM28), which is an epigenetic modifier implicated in gene transcription and cell differentiation, is essential to mediate sprouting angiogenesis. We observed that knockdown of TRIM28 ortholog in zebrafish resulted in developmental vascular defect with disorganized and reduced vasculatures. Consistently, TRIM28 knockdown inhibited angiogenic sprouting of cultured endothelial cells (ECs), which exhibited increased mRNA levels of VEGFR1, Delta‐like (DLL) 3, and Notch2 but reduced levels of VEGFR2, DLL1, DLL4, Notch1, Notch3, and Notch4.The regulative effects of TRIM28 on these angiogenic factors were partially mediated by hypoxia‐inducible factor 1 α (HIF‐1α) and recombination signal‐binding protein for immunoglobulin kappa J region (RBPJκ). In vitro DNA‐binding assay showed that TRIM28 knockdown increased the association of RBPJκ with DNA sequences containing HIF‐1α‐binding sites. Moreover, the phosphorylation of TRIM28 was controlled by VEGF and Notch1 through a mechanism involving RBPJκ‐dual‐specificity phosphatase (DUSP)‐p38 MAPK, indicating a negative feedback mechanism. These findings established TRIM28 as a crucial regulator of VEGFR‐Notch signaling circuit through HIF‐1α and RBPJκ in EC sprouting angiogenesis.

Abstract Vascular smooth muscle cells (VSMCs) in the normal arterial media continually express contractile phenotypic markers which are reduced dramatically in response to injury. Tripartite motif‐containing proteins are a family of scaffold proteins shown to regulate gene silencing, cell growth, and differentiation. We here investigated the biological role of tripartite motif‐containing 28 (TRIM28) and tripartite motif‐containing 27 (TRIM27) in VSMCs. We observed that siRNA‐mediated knockdown of TRIM28 and TRIM27 inhibited platelet‐derived growth factor (PDGF)‐induced migration in human VSMCs. Both TRIM28 and TRIM27 can regulate serum response element activity and were required for maintaining the contractile gene expression in human VSMCs. At the same time, TRIM28 and TRIM27 knockdown reduced the expression of PDGF receptor‐β (PDGFRβ) and the phosphorylation of its downstream signaling components. Immunoprecipitation showed that TRIM28 formed complexes with TRIM27 through its N‐terminal RING‐B boxes‐Coiled‐Coil domain. Furthermore, TRIM28 and TRIM27 were shown to be upregulated and mediate the VSMC contractile marker gene and PDGFRβ expression in differentiating human bone marrow mesenchymal stem cells. In conclusion, we identified that TRIM28 and TRIM27 cooperatively maintain the endogenous expression of PDGFRβ and contractile phenotype of human VSMCs.