Cloning and Characterization of an Alternatively Spliced Form of SR Protein Kinase 1 That Interacts Specifically with Scaffold Attachment Factor-B

Eleni Nikolakaki,Rachel Kohen,Annette M Hartmann,Stefan Stamm,Elena Georgatsou,Thomas Giannakouros

doi:10.1074/jbc.m104755200

Abstract

Serine/arginine protein kinases have been conserved throughout evolution and are thought to play important roles in the regulation of mRNA processing, nuclear import, germline development, polyamine transport, and ion homeostasis. Human SRPK1, which was first identified as a kinase specific for the SR family of splicing factors, is located on chromosome 6p21.2-p21.3. We report here the cloning and characterization of SRPK1a, which is encoded by an alternatively processed transcript derived from the SRPK1 gene. SRPK1a contains an insertion of 171 amino acids at its NH(2)-terminal domain and is similar to SRPK1 in substrate specificity and subcellular localization. Moreover, both isoforms can induce alternative splicing of human tau exon 10 in transfected cells. Using the yeast two-hybrid assay, we found that the extended NH(2)-terminal domain of SRPK1a interacts with Scaffold Attachment Factor-B, a nuclear scaffold-associated protein. Confirmation of this interaction was provided by in vitro binding assays, as well as by co-immunoprecipitation from 293T cells doubly transfected with SRPK1a and SAF-B. Our studies suggest that different SRPK family members are uniquely regulated and targeted and thus the multiple SRPK kinases present in higher eukaryotes may perform specialized and differentiable functions.

Highlights

Serine/arginine protein kinases have been conserved throughout evolution and are thought to play important roles in the regulation of mRNA processing, nuclear import, germline development, polyamine transport, and ion homeostasis
Because it is well documented that human SRPK1 is mapped to chromosome 6p21.2-p21.3 [41] and the genomic sequence is available (EMBL data bank, locus HS422H11, accession number Z99128) we compared the sequence of the isolated clone with the genomic sequence
The sequence alignment revealed that the SRPK1 gene comprises 16 exons (Fig. 2A, see EMBL data bank, locus HS422H11, accession number Z99128, gene ϭ dJ422H11.1)

Summary

Introduction

Serine/arginine protein kinases have been conserved throughout evolution and are thought to play important roles in the regulation of mRNA processing, nuclear import, germline development, polyamine transport, and ion homeostasis. SRPK1a contains an insertion of 171 amino acids at its NH2-terminal domain and is similar to SRPK1 in substrate specificity and subcellular localization. Both isoforms can induce alternative splicing of human tau exon 10 in transfected cells. It has been proposed that the formation of complexes between SF2/ASF and SRPKs may modulate the subcellular distribution of SF2/ASF [21] The lack both of authentic SR proteins in the yeast genome and of alternative mRNA splicing in yeast suggests that these kinases play roles in the regulation of cellular processes in addition to that of mRNA splicing. Sky1p was found to regulate nuclear import of Npl3p by promoting the interaction between Npl3p

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Conclusion