Transformer 2β1 (Tra2β1) is a splicing effector protein composed of a core RNA recognition motif flanked by two arginine-serine-rich (RS) domains, RS1 and RS2. Although Tra2β1-dependent splicing is regulated by phosphorylation, very little is known about how protein kinases phosphorylate these two RS domains. We now show that the serine-arginine protein kinase-1 (SRPK1) is a regulator of Tra2β1 and promotes exon inclusion in the survival motor neuron gene 2 (SMN2). To understand how SRPK1 phosphorylates this splicing factor, we performed mass spectrometric and kinetic experiments. We found that SRPK1 specifically phosphorylates 21 serines in RS1, a process facilitated by a docking groove in the kinase domain. Although SRPK1 readily phosphorylates RS2 in a splice variant lacking the N-terminal RS domain (Tra2β3), RS1 blocks phosphorylation of these serines in the full-length Tra2β1. Thus, RS2 serves two new functions. First, RS2 positively regulates binding of the central RNA recognition motif to an exonic splicing enhancer sequence, a phenomenon reversed by SRPK1 phosphorylation on RS1. Second, RS2 enhances ligand exchange in the SRPK1 active site allowing highly efficient Tra2β1 phosphorylation. These studies demonstrate that SRPK1 is a regulator of Tra2β1 splicing function and that the individual RS domains engage in considerable cross-talk, assuming novel functions with regard to RNA binding, splicing, and SRPK1 catalysis.
Digital Object Identifier (DOI)
This work was supported, in whole or in part, by National Institutes of Health Grants RO1 GM067969 (to J. A. A.) and a supplement to GM067969. The authors declare that they have no conflicts of interest with the contents of this article.
Jamros, Michael A.; Aubol, Brandon E.; Keshwani, Malik M.; Zhang, Zhaiyi; Stamm, Stefan; and Adams, Joseph A., "Intra-Domain Cross-Talk Regulates Serine-Arginine Protein Kinase 1-Dependent Phosphorylation and Splicing Function of Transformer 2β1" (2015). Molecular and Cellular Biochemistry Faculty Publications. 86.