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

Keiko Horiuchi,Takeshi Kawamura,Hiroko Iwanari,Riuko Ohashi,Makoto Naito,Tatsuhiko Kodama,Takao Hamakubo

doi:10.1074/jbc.m113.500397

Keiko Horiuchi, Takeshi Kawamura + Show 5 more

Open Access

https://doi.org/10.1074/jbc.m113.500397

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Abstract

Wilms' tumor 1-associating protein (WTAP) is a putative splicing regulator that is thought to be required for cell cycle progression through the stabilization of cyclin A2 mRNA and mammalian early embryo development. To further understand how WTAP acts in the context of the cellular machinery, we identified its interacting proteins in human umbilical vein endothelial cells and HeLa cells using shotgun proteomics. Here we show that WTAP forms a novel protein complex including Hakai, Virilizer homolog, KIAA0853, RBM15, the arginine/serine-rich domain-containing proteins BCLAF1 and THRAP3, and certain general splicing regulators, most of which have reported roles in post-transcriptional regulation. The depletion of these respective components of the complex resulted in reduced cell proliferation along with G2/M accumulation. Double knockdown of the serine/arginine-rich (SR)-like proteins BCLAF1 and THRAP3 by siRNA resulted in a decrease in the nuclear speckle localization of WTAP, whereas the nuclear speckles were intact. Furthermore, we found that the WTAP complex regulates alternative splicing of the WTAP pre-mRNA by promoting the production of a truncated isoform, leading to a change in WTAP protein expression. Collectively, these findings show that the WTAP complex is a novel component of the RNA processing machinery, implying an important role in both posttranscriptional control and cell cycle regulation.

Highlights

Wilms’ tumor 1-associating protein (WTAP) is a ubiquitously expressed nuclear protein that is required for mammalian early embryo development and cell cycle progression
The WTAP Complex Is Required for Cell Proliferation—We examined the effect of the respective depletion of the major components Hakai, Virilizer, KIAA0853, BCLAF1, THRAP3, and RBM15 on cell proliferation in HUVECs
The WTAP Complex Autoregulates Alternative Splicing of WTAP Pre-mRNA—While investigating the effect of the depletion of WTAP-interacting proteins by siRNA, we found that WTAP protein expression was up-regulated in BCLAF1/ THRAP3, Virilizer, KIAA0853, and Hakai siRNA-treated cells (Fig. 6A)

Summary

Background

WTAP is a ubiquitously expressed nuclear protein that is required for mammalian early embryo development and cell cycle progression. We show that WTAP forms a novel protein complex including Hakai, Virilizer homolog, KIAA0853, RBM15, the arginine/ serine-rich domain-containing proteins BCLAF1 and THRAP3, and certain general splicing regulators, most of which have reported roles in post-transcriptional regulation. The depletion of these respective components of the complex resulted in reduced cell proliferation along with G2/M accumulation. We found that the WTAP complex regulates alternative splicing of the WTAP pre-mRNA by promoting the production of a truncated isoform, leading to a change in WTAP protein expression These findings show that the WTAP complex is a novel component of the RNA processing machinery, implying an important role in both posttranscriptional control and cell cycle regulation. Our findings suggest that WTAP localizes to nuclear speckles through the interaction of BCLAF1 or THRAP3 and takes part in posttranscriptional regulation

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION