Wilms’ Tumor 1–Associating Protein Regulates the Proliferation of Vascular Smooth Muscle Cells

Abstract

Abstract-Smooth muscle cells (SMCs) are called on to proliferate during vascular restructuring but must return to a nonproliferative state if remodeling is to appropriately terminate. To identify mediators of the reacquisition of replicative quiescence, we undertook gene expression screening in a uniquely plastic human SMC line. As proliferating SMCs shifted to a contractile and nonproliferative state, expression of TIMP-3, Axl, and KIAA0098 decreased whereas expression of complement C1s, cathepsin B, cellular repressor of E1A-activated genes increased. Wilms' tumor 1-associating protein (WTAP), a nuclear constituent of unknown function, was also upregulated as SMCs became nonproliferative. Furthermore, WTAP in the intima of injured arteries was substantially upregulated in the late stages of repair. Introduction of WTAP complementary DNA into human SMCs inhibited their proliferation, with a corresponding decrease in DNA synthesis and an increase in apoptosis. Knocking down endogenous WTAP increased SMC proliferation, because of increased DNA synthesis and G 1 /S phase transition, together with reduced apoptosis. WTAP was found to associate with the Wilms' tumor-1 protein in human SMCs and WTAP overexpression inhibited the binding of WT1 to an oligonucleotide containing a consensus WT1 binding site, whereas WTAP knockdown accentuated this interaction. Expression of the WT1 target genes, amphiregulin and Bcl-2, was suppressed in WTAP-overexpressing SMCs and increased in WTAP-deficient SMCs. Moreover, exogenous amphiregulin rescued the antiproliferative effect of WTAP. These findings identify WTAP as a novel regulator of the cell cycle and cell survival and implicate a WTAP-WT1 axis as a novel pathway for controlling vascular SMC phenotype. (Circ Res. 2006;99:1338-1346.)Key Words: amphiregulin Ⅲ smooth muscle cells Ⅲ Wilms' tumor 1-associating protein Ⅲ vascular smooth muscle cell proliferation P henotype plasticity is a feature of adult vascular smooth muscle cells (SMCs). A widely studied example of this is the dedifferentiation of mature, nonproliferative SMCs into proliferative SMCs, a process central to vascular remodeling. 1,2 Although less well studied, an equally important manifestation of SMC plasticity is the reverse shift, whereby proliferative adult SMCs convert back to a nonproliferative state. This particular phenotype switch is essential for limiting SMC accumulation and for terminating vascular remodeling. As such, the regulatory factors that drive proliferative SMCs into a nonproliferative state, and hold them in that state, are critical for effective vascular remodeling and for limiting vascular disease.We have generated unique lines of nonimmortalized human SMCs that are capable of converting between proliferative and nonproliferative states. 2,3 In the presence of serum, these SMCs proliferate, migrate, and elaborate extracellular matrix similar to primary SMCs. On withdrawal of serum however they undergo a reproducible program of cellular maturation whereby they exit the cell cycle, migrate...

Identification of Wilms' Tumor 1-associating Protein Complex and Its Role in Alternative Splicing and the Cell Cycle

“…On the other hand, Small et al (19,20) reported that WTAP inhibits SMC proliferation and activates apoptosis by modulating the alternative splicing of the apoptosis regulator survivin. In addition, recent studies have shown that WTAP is overexpressed in glioblastoma (21) and cholangiocarcinoma (22) and promotes the migration and invasion of these cancer cells with an effect on cell proliferation under a condition of 1% FBS.…”

Nuclear Degradation of Wilms Tumor 1-associating Protein and Survivin Splice Variant Switching Underlie IGF-1-mediated Survival

“…WTAP (Wilms tumor 1-associating protein) is a recently identified nuclear protein that, as its name implies, can interact with the WT1 suppressor protein (3,4). The precise molecular actions of WTAP are not well understood, but the importance of this protein is highlighted by the early lethality of WTAP-null mouse embryos (5,6).…”

“…Furthermore, overexpression of WTAP in cultured SMCs suppressed their accumulation, whereas WTAP knockdown stimulated population growth. These effects were mediated, at least in part, by the capacity for WTAP to activate apoptosis (4).…”

“…One group has reported that WTAP stabilizes cyclin A2 mRNA in human umbilical vein endothelial cells (5). Another level of action relates to the ability of WTAP to prevent WT1 from binding to its transcriptional target DNA (4). There is also evidence that WTAP may act as a splicing regulator (7).…”

IGF-1 deficiency in a critical period early in life influences the vascular aging phenotype in mice by altering miRNA-mediated post-transcriptional gene regulation: implications for the developmental origins of health and disease hypothesis

“…WTAP is a newly discovered component of the m6 A methyltransferase complex, which plays a critical role in epitranscriptomic regulation of RNA metabolism (Ping et al 2014). Recent studies show that WTAP inhibits the proliferation of vascular smooth muscle cells and endothelial cells and promotes apoptosis, regulating vascular remodeling (Small et al 2006(Small et al , 2007. During development of the vasculature IGF-1 was shown to downregulate WTAP, which is necessary for IGF-1 to confer its antiapoptotic effects, regulating smooth muscle cell fate (Small and Pickering 2009).…”