Hsp60 Regulation of Prostate Cancer Progression

Mitochondrial protein homeostasis (proteostasis) has been implicated in cancer and is
regulated by mitochondrial unfolded protein response (UPRmt). However, it is unknown whether
UPRmt promotes tumorigenesis and whether it could be targeted for therapeutic benefit in prostate
cancer (PCa). This proposal will define how heat shock protein 60 (HSP60), a key component of
UPRmt, promotes aggressive and resistant PCa. Using genetically-engineered triple knockout (TKO:
deletion of Pten, Trp53, and Rb1) tumors, we observed that HSP60 is upregulated in aggressive
tumors and castration-resistant prostate cancer (CRPC) compared to WT prostatic tissues. TCGA
data analysis and our preliminary data using human PCa-specific TMAs demonstrated that HSP60
is upregulated in prostate tumors with higher Gleason Scores. HSP60-silencing induced caspase
activation and inhibited cellular proliferation whereas HSP60 overexpression promoted cancer cell
survival and proliferation. We provide the first evidence that, genetic deletion of HSP60 in TKO
mouse and inhibition of HSP60 oligomerization by introducing HSP60D3G KI during prostate
tumorigenesis, reduced tumor burden in vivo. We observed that activating transcription factor 5
(ATF5), specific for HSP60 expression and UPRmt activation, was upregulated with higher Gleason
Scores, and ATF5 was translocated to nucleus during stress. Using in silico analysis, we have
identified a novel UPRmt inhibitor (referred to as DCEM1), which induced robust apoptosis in PCa
cells and blocked tumor growth in vivo. Based on these findings, we hypothesized that HSP60-
dependent mitochondrial unfolded protein response promotes cancer cell adaptation during
tumor progression and therapeutic resistance in PCa. Identification of UPRmt inhibitor provides
alternative treatment option for patients with PCa. We propose the following Specific Aims to test
this hypothesis.
Aim 1. Define the role of transcription factor ATF5 in activating mitochondrial unfolded protein
response. Aim 2: Evaluate whether HSP60 oligomerization maintains functional mitochondria and
inhibits apoptosis to develop aggressive PCa. Aim 3. Explore the clinical relevance of HSP60
inhibition using patient-derived xenografts (PDXs) and primary tumor cells.
Impact: The findings will provide fundamental understanding on how UPRmt is activated and
how persistent mitochondrial stress is attenuated by UPRmt leading to development of aggressive
and lethal PCa. Identification of unique UPRmt inhibitor represents a new therapeutic vulnerability in
PCa that does not rely on androgen modulation. Therefore, UPRmt inhibition by DCEM1 will have
greater therapeutic benefits for patients with androgen-dependent and androgen-independent
CRPC.

Grant Number: 5R01CA246437-05
NIH Institute/Center: NIH
Principal Investigator: Dhyan Chandra