Studies of Exon-Junction Complex Heterogeneity
Studies of Exon-Junction Complex Heterogeneity
Despite a long appreciation for the role of NMD in destroying faulty, disease-causing mRNAs and maintaining normal, physiologic mRNA abundance, additional effectors that regulate NMD activity in mammalian cells continue to be identified. A haploid-cell genetic screen for NMD effectors that we developed has unexpectedly identified 13 proteins constituting the AKT signaling pathway.
We have shown that AKT supersedes UPF2 in exon-junction complexes (EJCs) that are devoid of RNPS1 but contain CASC3, defining an unanticipated insulin-stimulated EJC. Without altering UPF1 RNA binding or ATPase activity, AKT-mediated phosphorylation of the UPF1 CH domain at T151 augments UPF1 helicase activity, which is critical for NMD and also decreases the dependence of helicase activity on ATP. We demonstrate that upregulation of AKT signaling contributes to the hyperactivation of NMD that typifies Fragile X syndrome, as exemplified using FMR1-KO neural stem cells derived from induced pluripotent stem cells.
Open Project: We aim to understand the “rules” for EJC formation, i.e. which constituents can co-exist in the same EJC, and which are excluded by the presence of another constituent. Since EJC formation begins on the spliceosome, we aim to understand when commitment to the various EJC types begins, and how that EJC type can be influenced by effector-mediated post-translational modifications of EJC constituents. It is important to understand not only how, but why different EJCs exist on particular mRNAs during cell growth and differentiation processes.