Regulation of translation in stress conditions is critical for maintaining protein

homeostasis (proteostasis) and successfully reacting to changes in the cellular and

external environment. Proteotoxic stress, which leads to the accumulation of

misfolded proteins, can occur in diverse conditions; on the one hand, environmental

perturbations, such as heat stress, oxidative stress, ER stress and more, which cells

can experience throughout their lifetime in an external or physiological setting; On the

other hand, pathological misfolding can be caused by various neurodegenerative

disorders, such as Amyotrophic lateral sclerosis (ALS) and Huntington’s disease,

which lead to protein aggregation. Translational control is tightly coupled to

proteostasis regulation. In all of these conditions, translation can be regulated at

diverse layers and mechanisms, from classical pathways of translation initiation

through specific mechanisms regulating translation of subsets of mRNAs, to

regulation of ribosome-associated proteins and more. However, which of these

mechanisms plays a role in the various scenarios of proteostasis assaults, and how

translation is controlled globally and specifically, is still largely unresolved.

In this work, I describe the study of proteotoxicity-mediated control of translation,

examined at two different layers of regulation. First, I characterized stress-mediated

regulation of ribosome-associated chaperones, using a new method that I established,

fluorescent polysome profiling. Here I revealed dynamic regulation of the ribosome

associated chaperone mRAC in heat stress in human cells. In the second part, I

performed a transcriptome-wide analysis of transcription and translation regulation in

response to protein aggregation of mutant Huntingtin, the protein causing the

Huntington's Disease. Importantly, I was able to separate pure populations of cells

expressing aggregated proteins from those expressing mutant HTT that is not

aggregated. I characterized several gene expression programs, and found several that

were controlled exclusively at the level of translation. Furthermore, I observed a non-classical activation of ER stress pathways, including down-regulation of ER-targeted

proteins and additional changes suggesting dysregulation of proteostasis.

In summary, my study sheds light on the regulation of translation in stress conditions,

revealing interesting details of regulation under adaptive or pathological proteotoxic

stress conditions.