Physiological functions of Wilms’ tumor 1-associating protein and its role in tumourigenesis

The Wilms’ tumor-associated gene WT1 encodes a tumor suppressor gene, which is implicated in renal differentiation and development of adult urogenital system. Wilms’ tumor 1-associating protein (WTAP) is initially identified as a nuclear protein that specifically interacts with WT1 in both in vitro and in vivo assays. WTAP is ubiquitously expressed in different tissues and various growth periods, and its expression is involved in cell cycle, RNA splicing and stabilization, N6-methyladenosine RNA modification, cell proliferation, and apoptosis as well as embryonic development. In the present review, we aimed to summarize the functions of WTAP in various physiological and pathological processes, in particular with regard to the current knowledge about the role of WTAP in tumorigenesis of different cancers.     

mTORC1 stimulates cell growth through SAM synthesis and m6A mRNA-dependent control of protein synthesis

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Degradation of WTAP blocks antiviral responses by reducing the m6A levels of IRF3 and IFNAR1 mRNA

N ⁶‐methyladenosine (m⁶A) is a chemical modification present in multiple RNA species and is most abundant in mRNAs. Studies on m⁶A reveal its comprehensive roles in almost every aspect of mRNA metabolism, as well as in a variety of physiological processes. Although some recent discoveries indicate that m⁶A can affect the life cycles of numerous viruses as well as the cellular antiviral immune response, the roles of m⁶A modification in type I interferon (IFN‐I) signaling are still largely unknown. Here, we reveal that WT1‐associated protein (WTAP), one of the m⁶A “writers”, is degraded via the ubiquitination‐proteasome pathway upon activation of IFN‐I signaling. With the degradation of WTAP, the m⁶A levels of IFN‐regulatory factor 3 (IRF3) and interferon alpha/beta receptor subunit 1 (IFNAR1) mRNAs are reduced, leading to translational suppression of IRF3 and instability of IFNAR1 mRNA. Thus, the WTAP‐IRF3/IFNAR1 axis may serve as negative feedback pathway to fine‐tune the activation of IFN‐I signaling, which highlights the roles of m⁶A in the antiviral response by dictating the fate of mRNAs associated with IFN‐I signaling.     

Wilms’ tumor 1-associating protein complex regulates alternative splicing and polyadenylation at potential G-quadruplex-forming splice site sequences

Wilms’ tumor 1-associating protein (WTAP) is a core component of the N6-methyladenosine (m6A)-methyltransferase complex, along with VIRMA, CBLL1, ZC3H13 (KIAA0853), RBM15/15B, and METTL3/14, which generate m6A, a key RNA modification that affects various processes of RNA metabolism. WTAP also interacts with splicing factors; however, despite strong evidence suggesting a role of Drosophila WTAP homolog fl(2)d in alternative splicing (AS), its role in splicing regulation in mammalian cells remains elusive. Here we demonstrate using RNAi coupled with RNA-seq that WTAP, VIRMA, CBLL1, and ZC3H13 modulate AS, promoting exon skipping and intron retention in AS events that involve short introns/exons with higher GC content and introns with weaker polypyrimidine-tract and branch points. Further analysis of GC-rich sequences involved in AS events regulated by WTAP, together with minigene assay analysis, revealed potential G-quadruplex formation at splice sites where WTAP has an inhibitory effect. We also found that several AS events occur in the last exon of one isoform of MSL1 and WTAP, leading to competition for polyadenylation. Proteomic analysis also suggested that WTAP/CBLL1 interaction promotes recruitment of the 3′-end processing complex. Taken together, our results indicate that the WTAP complex regulates AS and alternative polyadenylation via inhibitory mechanisms in GC-rich sequences.     

mTORC1 promotes cell growth via m6A-dependent mRNA degradation

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RNA甲基化酶WTAP对乳腺癌MCF-7和耐阿霉素MCF-7/ADR细胞迁移的影响

为了深入探讨乳腺癌治疗耐药的发生机制并寻找乳腺癌治疗耐药的潜在治疗手段,我们以乳腺癌MCF-7和耐阿霉素MCF-7/ADR细胞为研究对象,研究RNA甲基化酶WTAP对其迁移的影响。MTT试验发现阿霉素对MCF-7细胞活力的抑制作用大于对MCF-7/ADR细胞的抑制作用。qPCR和western-blot试验发现WTAP在耐阿霉素细胞MCF-7/ADR中高表达,同时transwell试验发现在MCF-7细胞中增加WTAP的表达对MCF-7细胞的迁移没有影响,而在MCF-7/ADR细胞中敲低WTAP的表达会抑制MCF-7/ADR细胞的迁移。western-blot试验进一步证明了这一作用是通过抑制上皮间质转化(EMT)来发挥的。这一发现有助于为乳腺癌的临床治疗提供新的理论依据并为乳腺癌的治疗提供新的策略。