Poster abstracts
Poster number 71 submitted by Vikas Kaushik
mTORC2 phosphorylation induces configurational changes in IMP1 resulting in modulation of RNA recognition
Vikas Kaushik (Biochemistry and Molecular Biology, Saint Louis University School of Medicine), Abhinav Vayyeti (GCE4All Research Center, Oregon State University), Rahul Chadda (Biochemistry and Molecular Biology, Saint Louis University School of Medicine), Richard Cooley (GCE4All Research Center, Oregon State University, Corvalis, OR ), Ryan Mehl (GCE4All Research Center, Oregon State University, Corvalis, OR ), Edwin Antony (Biochemistry and Molecular Biology, Saint Louis University School of Medicine)
Abstract:
RNA binding proteins (RBPs) have important functions in the regulation of gene expression. One such family of RBPs, insulin like growth factor 2 mRNA binding proteins (IMP), consists of IMP1, IMP2, and IMP3 paralogs. These are onco-fetal, highly conserved, post-transcriptional regulators of mRNA stability, degradation, localization, and translation. Among the IMP family, IMP1 and IMP3 are found to be re-expressed in several aggressive cancer types. Structurally, these proteins consist of 6 RNA binding domains, 2 N-terminal RNA recognition motifs (RRM1 and RRM2), and 4 ribonucleoprotein K homology (KH1, KH2, KH3, and KH4) domains which are connected by flexible linkers. The fundamental mechanism of how these proteins recognize specific mRNA targets is not known. We propose that specific arrangements of the domains (configurations) dictate how these proteins bind to and regulate mRNA targets. IMP1 is phosphorylated by the mTOR complex 2 kinase at position Ser181 (Dai et al., 2013) leading to regulation of IGF2 mRNA which is required for normal embryogenesis. Ser-181 is positioned within a disordered linker between the RRM2 and KH1 domains. To decipher how this modification regulates IMP1 activity we generated site-specifically phosphorylated IMP1 at Ser181 using mutant elongation factor proteins (EF-Sep), phosphoseryl-tRNA synthetase, and phosphoseryl-tRNA (tRNASep). We observed a three-fold decrease in RNA binding affinity of the phosphorylated IMP1. Interestingly, we observe that phosphorylation in this linker region alters the configurational arrangement of RRM and KH domains.
Keywords: RNA Binding Proteins (RBPs), phosphoserine, mTOR