# Role of HSC70 in protein synthesis

> **NIH NIH R01** · UNIVERSITY OF CALIFORNIA, SAN FRANCISCO · 2022 · $323,000

## Abstract

Project Summary/Abstract
Intracellular bacteria often secrete proteins (effectors) that hijack and rewire cellular pathways to establish their
replicative niche. Studying the mechanisms by which these bacterial proteins function have frequently led to the
identification of key cellular processes. Given that protein synthesis is essential to sustain cellular life and
function, several bacteria manipulate host cell protein synthesis. We recently discovered that the intracellular
bacterium, Legionella pneumophila (L.p.) secretes a eukaryotic-serine-threonine-protein-kinase (eSTPK)
effector called LegK4, that translocates into the host cell cytosol and phosphorylates the chaperone HSC70 on
T495 (pHSC70). Interestingly, this single phosphorylation causes a global block in protein synthesis. Often,
bacterial proteins mimic the activities of host proteins to usurp their cellular function. Given that HSC70 plays
diverse roles in the cell that includes the regulation of critical cellular processes such as protein homeostasis,
we studied whether a host kinase was capable of phosphorylating HSC70 on T495. Indeed, we discovered that
treatment of cells with methyl methanesulfonate, an alkylating agent that causes DNA damage, results in the
accumulation of pHSC70. Global mRNA translation is blocked during the DNA damage response (DDR) and it
is known that the type of stressor determines the mechanism of the block. For example, ionizing radiation and
topoisomerase II inhibition leads to an inhibition of mTOR signaling, while UV exposure leads to the
phosphorylation of eukaryotic initiation factor 2 by the kinase GCN2. However, the role of pHSC70 in inhibiting
protein synthesis during the DDR has never been studied. Here, we propose to investigate the role of pHSC70
in response to DNA damage and elucidate the mechanisms by which pHSC70 leads to protein synthesis
attenuation.
In the first aim, we will use biochemical and fluorescence-based assays to determine how phosphorylation of
HSC70 affects its chaperone function. In the second aim, we will perform polysome runoff assays to determine
which step of protein synthesis is blocked when HSC70 is phosphorylated. In addition, we propose to identify
the proteins that escape the protein synthesis block mediated by pHSC70. Finally, in the third aim, we will identify
the kinases that phosphorylate HSC70 during the DNA damage response and the spatio-temporal regulation of
signaling events that link the stress induced DNA damage response to pHSC70 and protein synthesis inhibition.
Overall, the aims of this proposal will help elucidate the role of a multifunctional chaperone in mediating protein
synthesis inhibition during DDR. The results of this study will not only be beneficial for the investigators studying
HSC70, but also those that study the DNA damage response and host-pathogen interactions.

## Key facts

- **NIH application ID:** 10520573
- **Project number:** 1R01GM144378-01A1
- **Recipient organization:** UNIVERSITY OF CALIFORNIA, SAN FRANCISCO
- **Principal Investigator:** Shaeri Mukherjee
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $323,000
- **Award type:** 1
- **Project period:** 2022-07-20 → 2026-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10520573

## Citation

> US National Institutes of Health, RePORTER application 10520573, Role of HSC70 in protein synthesis (1R01GM144378-01A1). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10520573. Licensed CC0.

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