Insulin Signaling and the Heat Shock Response Modulate Protein Homeostasis in theCaenorhabditis elegansIntestine during Infection

ABSTRACTCells exposed to heat shock induce a conserved gene expression program – the heat shock response (HSR) – encoding chaperones like Hsp70 and other protein homeostasis (proteostasis) factors. Heat shock also triggers proteostasis factors to form subcellular quality control bodies, but the relationship between these spatial structures and the HSR is unclear. Here we show that localization of the J-protein Sis1 – a co-chaperone for Hsp70 – controls HSR activation in yeast. Under nonstress conditions, Sis1 is concentrated in the nucleoplasm where it promotes Hsp70 binding to the transcription factor Hsf1, repressing the HSR. Upon heat shock, Sis1 forms an interconnected network with other proteostasis factors that spans the nucleolus and the surface of the cortical ER. We propose that localization of Sis1 to this network directs Hsp70 activity away from Hsf1 in the nucleoplasm, leaving Hsf1 free to induce the HSR. In this manner, Sis1 couples HSR activation to the spatial organization of the proteostasis network.One sentence summaryLocalization of the J-protein Sis1 to a subcellular network of proteostasis factors activates the heat shock response.

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Subcellular localization of the J-protein Sis1 regulates the heat shock response

The Journal of Cell Biology ◽

10.1083/jcb.202005165 ◽

2020 ◽

Vol 220 (1) ◽

Author(s):

Zoë A. Feder ◽

Asif Ali ◽

Abhyudai Singh ◽

Joanna Krakowiak ◽

Xu Zheng ◽

...

Keyword(s):

Heat Shock ◽

Heat Shock Response ◽

Spatial Organization ◽

Protein Homeostasis ◽

Shock Response ◽

Conserved Gene ◽

Encoding Protein ◽

Expression Program ◽

The Relationship ◽

J Protein

Cells exposed to heat shock induce a conserved gene expression program, the heat shock response (HSR), encoding protein homeostasis (proteostasis) factors. Heat shock also triggers proteostasis factors to form subcellular quality control bodies, but the relationship between these spatial structures and the HSR is unclear. Here we show that localization of the J-protein Sis1, a cofactor for the chaperone Hsp70, controls HSR activation in yeast. Under nonstress conditions, Sis1 is concentrated in the nucleoplasm, where it promotes Hsp70 binding to the transcription factor Hsf1, repressing the HSR. Upon heat shock, Sis1 forms an interconnected network with other proteostasis factors that spans the nucleolus and the surface of the endoplasmic reticulum. We propose that localization of Sis1 to this network directs Hsp70 activity away from Hsf1 in the nucleoplasm, leaving Hsf1 free to induce the HSR. In this manner, Sis1 couples HSR activation to the spatial organization of the proteostasis network.

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Protein Homeostasis: A Key Target in Myeloma

Blood ◽

10.1182/blood.v130.suppl_1.sci-8.sci-8 ◽

2017 ◽

Vol 130 (Suppl_1) ◽

pp. SCI-8-SCI-8

Author(s):

Lawrence H. Boise

Keyword(s):

Heat Shock ◽

Plasma Cell ◽

Heat Shock Response ◽

Plasma Cells ◽

Proteasome Inhibitors ◽

Proteasome Inhibition ◽

Myeloma Cell ◽

Protein Homeostasis ◽

Unfolded Protein ◽

Shock Response

Multiple myeloma is a disease of long-lived plasma cells that remains incurable in the majority of patients. However advances in the treatment have been made in the last 20 years resulting in significant improvement in the survival of patients with this disease. Interestingly almost all of these advances have been made through the targeting of pathways or molecules that are shared between normal and malignant plasma cells and are not due to the precision targeting of myeloma cell dependencies associated with the transformation process. Most notably targeting both specific and bulk protein homeostasis through the action of IMiDs and proteasome inhibitors have become the backbone for the treatment of newly diagnosed myeloma in the United States. We have focused on proteasome function and regulation to better understand why a macromolecular structure that is present and functions in every cell in the body is such an effective target for myeloma therapy. Our initial findings indicated that proteasome inhibition activated an endoplasmic reticulum stress response known as the unfolded protein response (UPR). The UPR is required for normal differentiation and maintenance of plasma cells, although our initial findings suggesting that the PERK arm of the response, which is not required for normal plasma cell maintenance was activated by proteasome inhibitors. We determined that the likely source of unfolded protein was immunoglobulin produced by myeloma cells and that the fate of immunoglobulin was a key determinant of sensitivity to proteasome inhibition. We have now focused on additional factors that determine the response to proteasome inhibition and consistent with previous findings have demonstrated that activation of heat shock response is a early protective event following proteasome inhibition. However we were unable to demonstrate that any single heat shock protein was sufficient to alter the response to proteasome inhibition. Rather it was the activation of the heat shock response itself and that protection was only efficiently blocked by inhibition of the transcriptional regulator of the response, HSF1. HSF1 is activated through post-translational modifications and proteasome inhibition results in phosphorylation of HSF1 at several sites, most notably S326. This can be blocked with the multi-kinase inhibitor TG02 that effectively blocks the proteasome inhibitor-induced heat shock response and sensitizes myeloma cells to proteasome inhibitor-induced cell death. Based on these findings, the combination of TG02 and carfilzomib are being tested clinically. The cellular response to proteasome inhibitors is also controlled through the regulation of proteasome assembly. We have recently demonstrated that 14-3-3ζ an anti-apoptotic phospho-serine binding protein, can limit proteasome assembly and activity through its binding to the PA28α subunit of the 11S regulator. This significantly lowers proteasome capacity and sensitizes cells to proteasome inhibition but not to other therapeutic agents. Finally in addition to regulation of bulk protein homeostasis, targeting of specific protein turnover has proven effective in myeloma treatment. IMiDs can alter the ability of the E3 ligase cereblon to recognize substrates for ubiquitination, resulting in the degradation of key B cell transcription factors IKZF1/3. These can regulate the plasma cell maintenance factor IRF4 as well as play a direct role in the regulation plasma cell superenhancers that control the expression of oncogenes translocated in myeloma. Another key mediator of myeloma cell survival, MCL1 is regulated via protein stability and can targeted in this manner. Direct and indirect targeting of MCL1 will be discussed. Disclosures Boise: Abbvie: Consultancy; Eli Lilly and Company: Research Funding.

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