SRPK2: A Differentially Expressed SR Protein-specific Kinase Involved in Mediating the Interaction and Localization of Pre-mRNA Splicing Factors in Mammalian Cells

Abstract

Abstract. Reversible phosphorylation plays an important role in pre-mRNA splicing in mammalian cells. Two kinases, SR protein-specific kinase (SRPK1) and Clk/Sty, have been shown to phosphorylate the SR family of splicing factors. We report here the cloning and characterization of SRPK2, which is highly related to SRPK1 in sequence, kinase activity, and substrate specificity. Random peptide selection for preferred phosphorylation sites revealed a stringent preference of SRPK2 for SR dipeptides, and the consensus derived may be used to predict potential phosphorylation sites in candidate arginine and serine-rich (RS) domain–containing proteins. Phosphorylation of an SR protein (ASF/SF2) by either SRPK1 or 2 enhanced its interaction with another RS domain–containing protein (U1 70K), and overexpression of either kinase induced specific redistribution of splicing factors in the nucleus. These observations likely reflect the function of the SRPK family of kinases in spliceosome assembly and in mediating the trafficking of splicing factors in mammalian cells. The biochemical and functional similarities between SRPK1 and 2, however, are in contrast to their differences in expression. SRPK1 is highly expressed in pancreas, whereas SRPK2 is highly expressed in brain, although both are coexpressed in other human tissues and in many experimental cell lines. Interestingly, SRPK2 also contains a proline-rich sequence at its NH2 terminus, and a recent study showed that this NH2-terminal sequence has the capacity to interact with a WW domain protein in vitro. Together, our studies suggest that different SRPK family members may be uniquely regulated and targeted, thereby contributing to splicing regulation in different tissues, during development, or in response to signaling.

Interactions between two fission yeast serine/arginine-rich proteins and their modulation by phosphorylation

“…addition, the SR proteins are phosphorylated predominately on serine residues in the RS domain [14,16,17], presumably by SR protein-specific kinases, including the SR protein kinases (SRPKs) [17,18] and the Cdc2\Cdc28-like kinases (CLK\STY) [16]. The phosphorylation affects the cellular localization and the protein-RNA interactions of the SR proteins [19].…”

Nuclear Relocalization of the Pre-mRNA Splicing Factor PSF during Apoptosis Involves Hyperphosphorylation, Masking of Antigenic Epitopes, and Changes in Protein Interactions

“…A number of mammalian kinases have been shown to cause disassembly of nuclear speckles and relocalization of splicing factors, and to subsequently affect splicing factor activity. SRPK-1/2, Clk-1/2/3/4, cdc2-kinase, cyclin Ecdk2, topoisomerase I, U1 70-kDa associated kinase, cGMPdependent kinase, and lamin B-receptor kinase were all shown to phosphorylate SR proteins and other splicing factors in vitro (Woppmann et al, 1993;Gui et al, 1994;Colwill et al, 1996;Nikolakaki et al, 1996;Rossi et al, 1996;Nayler et al, 1997;Duncan et al, 1998;Kuroyanagi et al, 1998;Okamoto et al, 1998;Seghezzi et al, 1998;Wang et al, 1998;Koizumi et al, 1999;Wang et al, 1999). In addition, some of these kinases were shown to affect the splicing activity of such factors (Mermoud et al, 1994;Cao et al, 1997;Xiao and Manley, 1998;Prasad et al, 1999).…”

“…How all of these enzymes work in concert in vivo, if at all, is unknown. Cell-and tissue-specific differences in expression of these kinases (Nayler et al, 1997;Kuroyanagi et al, 1998;Wang et al, 1998;Papoutsopoulou et al, 1999) can only provide a partial explanation. A more likely hypothesis is that different kinases are recruited to nuclear speckles during different cell states and phosphorylate splicing factors in a manner specific to their biochemical properties.…”

Regulation of Alternative Splicing of Human Tau Exon 10 by Phosphorylation of Splicing Factors

“…In the nucleus, factors involved in pre-mRNA processing are concentrated in speckles-dynamic structures (Misteli et al, 1997) that are sensitive to phosphorylation (Nayler et al, 1998b). A number of kinases, phosphorylating RS domains, have been described, among them a U1 70K-associated kinase (Woppmann et al, 1993), SRPK1 (Gui et al, 1993), and SRPK2 (Wang et al, 1998). In addition, four kinases termed CLK (cdc2-like kinases) have been shown to phosphorylate SR proteins and to regulate their subnuclear localization (Colwill et al, 1996a,b;Nayler et al, 1997Nayler et al, , 1998b.…”