RNA interference knockdown of hU2AF35 impairs cell cycle progression and modulates alternative splicing of Cdc25 transcripts

U2AF is a heterodimeric splicing factor composed of a large (U2AF(65)) and a small (U2AF(35)) subunit. In humans, alternative splicing generates two U2AF(35) variants, U2AF(35)a and U2AF(35)b. Here, we used RNA interference to specifically ablate the expression of each isoform in HeLa cells. Our results show that knockdown of the major U2AF(35)a isoform reduced cell viability and impaired mitotic progression, leading to accumulation of cells in prometaphase. Microarray analysis revealed that knockdown of U2AF(35)a affected the expression level of similar to 500 mRNAs, from which > 90% were underrepresented relative to the control. Among mRNAs underrepresented in U2AF(35)a-depleted cells we identified an essential cell cycle gene, Cdc27, for which there was an increase in the ratio between unspliced and spliced RNA and a significant reduction in protein level. Furthermore, we show that depletion of either U2AF(35)a or U2AF(35)b altered the ratios of alternatively spliced isoforms of Cdc25B and Cdc25C transcripts. Taken together our results demonstrate that U2AF(35)a is essential for HeLa cell division and suggest a novel role for both U2AF(35) protein isoforms as regulators of alternative splicing of a specific subset of genes.