Cloning of human PRP4 reveals interaction with Clk1

Prp4 is a protein kinase of Schizosaccharomyces pombe identified through it s role in pre-mRNA splicing, and belongs to a kinase family including mamma lian serine/arginine-rich protein-specific kinases and Clks, whose substrat es are serine/arginine-rich proteins. We cloned human PRP4 (hPRP4) full-len gth cDNA and the antiserum raised against a partial peptide of hPRP4 recogn ized 170-kDa polypeptide in HeLa S3 cell extracts. Northern blot analysis r evealed that hPRP4 mRNA was ubiquitously expressed in multiple tissues. The extended NH2-terminal region of hPRP4 contains an arginine/serine-rich dom ain and putative nuclear localization signals. hPRP4 phosphorylated and int eracted with SF2/ASF, one of the essential splicing factors. Indirect immun ofluorescence analysis revealed that endogenous hPRP4 was distributed in a nuclear speckled pattern and colocalized with SF2/ASF in HeLa S3 cells. Fur thermore, hPRP4 interacted directly with Clk1 on its COOH terminus, and the arginine/serine-rich domain of hPRP4 was phosphorylated by Clk1 in vitro. Overexpression of Clk1 caused redistribution of hPRP4, from the speckled to the diffuse pattern in nucleoplasm, whereas inactive mutant of Clk1 caused no change of hPRP4 localization. These findings suggest that the NH2-termi nal region of hPRP4 may play regulatory roles under an unidentified signal transduction pathway through Clk1.