Interplay of Acetyltransferase EP300 and the Proteasome System in Regulating Heat Shock
Transcription Factor 1


 Abstract

The cytosolic stress response, also known as the heat-shock response (HSR), is one of the major defense mechanisms activated by cells to maintain the integrity of the cellular proteome under proteotoxic environmental conditions. It is characterized by the increased synthesis of heat-shock proteins (Hsps), mainly molecular chaperones and proteases which prevent the aggregation of misfolded proteins and mediate their refolding or degradation. It is generally accepted that the induction of the HSR is coordinated by the heat-shock transcription factor 1 (HSF1). However, many mechanistic aspects of the HSF1 regulation remain unclear.

In the present study, a genome-wide RNA interference screen was combined with an extensive biochemical analysis and quantitative proteomics to better understand the regulation of the HSR upon thermal stress. The usage of an endoribonuclease-prepared small interfering RNA (esiRNA) library represented a simple and efficient way to perform RNAi with minimal off-target effects. In the screening experiments novel positive and negative modulators of the stress response were identified, including proteins involved in chromatin remodeling, transcription, mRNA splicing, DNA damage repair, and proteolytic degradation. The diversity of the identified regulators suggests that induction and attenuation of the HSR integrate signals from different cellular pathways and are rather multi-factorial processes than single gene/protein events. The modulator proteins are localized in multiple cellular compartments with the majority having their primary location in the nucleus. A protein-protein interaction analysis revealed a HSR regulatory network, with chromatin modifiers and nuclear protein quality control components occupying hub positions. These observations are supported by quantitative proteomics experiments, which showed specific stress-induced reorganizations of the nuclear proteome, including the transient accumulation of chaperones and proteasomal subunits.

Moreover, we found that the acetyltransferase EP300 controls the cellular level of activatable HSF1. This involves acetylation of HSF1 at multiple lysines not required for function and results in stabilization of HSF1 against proteasomal turnover. Acetylation of functionally critical lysines during stress serves to fine-tune HSF1 activation. Finally, the nuclear proteasome system functions in attenuating the stress response by degrading activated HSF1 in a manner linked with the clearance of misfolded proteins.


 Speakers

Dr. Mirko Theis
R&D scientist, Eupheria Biotech GmbH

Dr. Mirko Theis worked at the Max Planck Institute of Molecular Cell Biology and Genetics in Dresden. There he co-developed the esiRNA technology for efficient and specific RNA interference and was one of the architects of genome-scale esiRNA libraries targeting the mouse and human transcriptome. Since 2010 he works as an R&D scientist at Eupheria Biotech.

Dr. Christian Löw
R&D Scientist

Dr. Christian Löw received his PhD from the Max Planck Institute of Biochemistry in Martinsried, Germany and currently works in the biotech industry. While in the Max Planck Institute, he focused on using genome-wide RNAi screens to identify modulators of cystosolic stress response.