The cellular localization of the murine serine/arginine-rich protein kinase CLK2 is regulated by serine 141 autophosphorylation

Pre-mRNA splicing is catalyzed by a multitude of proteins including serine/ arginine-rich (SR) proteins, which are thought to play a crucial role in th e formation of spliceosomes and in the regulation of alternative splicing. SR proteins are highly phosphorylated, and their kinases are believed to re gulate the recruitment of SR proteins from nuclear storage compartments kno wn as speckles. Recently, a family of autophosphorylating kinases termed CL K (CDC2/CDC28-like kinases) was shown to phosphorylate SR proteins and to i nfluence alternative splicing in overexpression systems. Here we used endog enous CLK2 protein to demonstrate that it displays different biochemical ch aracteristics compared with its overexpressed protein and that it is differ entially phosphorylated in vivo. Furthermore, CLK2 changed its nuclear loca lization upon treatment with the kinase inhibitor 5,6-dichloro-1-beta-D-rib ofuranosylbenzimidazole. We have also identified a CLK2 autophosphorylation site, which is highly conserved among all CLK proteins, and we show by sit e-directed mutagenesis that its phosphorylation influences the subnuclear l ocalization of CLK2. Our data suggest that CLK2 localization and possibly a ctivity are influenced by a balance of CLK2 autophosphorylation and the reg ulation by CLK2 kinases and phosphatases.