Li X., Manley J. a change in WTAP protein expression. Collectively, these findings show that this WTAP complex is a novel component of the RNA processing machinery, implying an important role in both posttranscriptional control and cell cycle regulation. sex Rabbit Polyclonal to Actin-pan determination pathway, where female-specific expression of the RNA-binding protein SXL (sex-lethal) regulates the alternative splicing of (male-specific-lethal 2) pre-mRNA, which control sex-specific alternative splicing and/or translation of the genes responsible for sexual differentiation and SDZ 220-581 behavior (4C8). Genetic analyses have revealed that SDZ 220-581 three additional genes are required for female-specific alternative splicing of (sans fille) (9), (virilizer) (10), and (11). Previous studies with FL(2)D (female lethal d) antibodies showed the physical conversation of FL(2)D with SXL (12, 13), VIR (12), Snf, U2AF, U2A50, and U2AF38 (13) in embryo nuclear extracts, suggesting that FL(2)D may take action at an early step in the SXL-dependent regulation of alternative splicing. Wilms’ tumor 1-associating protein (WTAP),2 a mammalian homologue of and assays (14). WTAP and WT1 are present together throughout the nucleoplasm as well as in speckles and colocalize in part with splicing factors (14). In addition, WTAP has been found in functional human spliceosomes (15). Other proteomic studies have also isolated WTAP as a component of the interchromatin granule clusters that correspond to nuclear speckles, where a variety of proteins involved in gene expression, such as transcription factors and splicing factors, are assembled, modified and sorted (16). Thus, WTAP is considered to have an evolutionarily conserved role in the regulation of splicing in mammalian cells. However, the detailed molecular mechanism is not well comprehended, although its essential role has been established in mouse early embryo development and cell cycle regulation (17, 18). We previously reported that WTAP is required for G2/M cell cycle transition through the stabilization of cyclin A2 mRNA and is vital for early mouse development (17). WTAP stabilizes cyclin A2 mRNA through the 3-UTR sequence, and a suppression of WTAP expression by siRNA resulted in G2 phase accumulation in HUVECs and human neonatal dermal fibroblasts. On the other hand, Small (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. The cell type-specific effect of WTAP on cell proliferation suggests a sensitive dependence on the cellular context, such as the requisite presence of certain binding partners. In the work presented here, we generated anti-WTAP monoclonal antibodies and identified the proteins that interact with WTAP using shotgun proteomics. The components of the WTAP complex are enriched in proteins that are involved in post-transcriptional regulation, such as pre-mRNA splicing, mRNA stabilization, polyadenylation, and/or mRNA export. Among them, double knockdown of the SR-like proteins BCLAF1 (BCL2-associated transcription factor 1) and THRAP3 (thyroid SDZ 220-581 hormone receptor-associated protein 3) resulted in a decrease in the speckle localization of WTAP, whereas the nuclear speckles were intact. Depletion of the major components of the complex, such as Virilizer homolog, KIAA0853, BCLAF1/THRAP3, Hakai, and RBM15 (RNA-binding motif protein 15) resulted in reduced cell proliferation with G2 phase accumulation. Moreover, we found that the WTAP complex regulates alternative splicing of the pre-mRNA and, thereby, SDZ 220-581 the expression of full-length WTAP protein. Taken together, our findings suggest that WTAP localizes to nuclear speckles through the interaction of BCLAF1 or THRAP3 and thus takes part in posttranscriptional regulation. EXPERIMENTAL PROCEDURES Cell Culture HUVECs (Lonza) were cultured in EGM2 medium (culture medium supplemented with growth factors) (Lonza) and used SDZ 220-581 within the first six passages. HeLa and HEK293T cells were grown in Dulbecco’s modified Eagle’s medium supplemented with 10% fetal bovine serum. Antibodies The expressed GST-full-length human WTAP protein (396 amino acids (aa)) was purified on glutathione-agarose beads (Sigma) and injected into BALB/c mice to produce the monoclonal antibodies H1122 and H1137. The Y6828 monoclonal antibody against the human WTAP N terminus was raised using a baculoviral display.