The role of translation initiation regulators in stress granule assembly and function

Abstract

Stress granules are cytoplasmic structures that contain proteins and mRNAs and are formed under stress conditions. It is proposed that SGs promote stress resistance, however the exact mechanism of their formation and function remains unclear. In this study I found that the S6 kinase 1 (S6K1) and S6 kinase 2 (S6K2), two of the main targets of mTORC1, have different roles in SG formation. S6K1 controls SG formation via regulating p-eIF2alpha levels while S6K2 is important for the persistence of the structures. In both cases the kinase activity of the proteins was required. To demonstrate the conserved nature of this mechanism in an animal model, it was shown that the orthologue of S6 kinase in C. elegans, RSKS-1, also induces SG formation and its knock-down sensitised worms to heat stress. Translation initiation is a highly regulated process and requires a large number of translation initiation factors (eIFs). The role of individual eIFs in translation inhibition and SG formation is unclear. In this study, I demonstrate that components of the translation initiation factor eIF3 localise to SGs and differentially regulate their formation and persistence. I also show that the RNA binding domain (RBD) and the nuclear localisation signal (NLS) of eIf3d, one of the subunits of eIF3 are important for promoting these functions. Finally, I show that mutations of the 5-Cap binding domain of eIF3d prohibit the recruitment of eIF3d to SGs and induce the formation of nuclear eIF3d bodies that do not coincide with known nuclear bodies. Overall, in this study I describe both S6 kinases and eIF3 subunits as novel regulators of SG formation and dynamics and demonstrate a novel connection between signalling pathways, translation regulation under stress and stress resistance.

Date of Award	31 Dec 2018
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Mark Ashe (Supervisor) & Alan Whitmarsh (Supervisor)