Heterozygous deletion of chromosome 17p renders prostate cancer vulnerable to inhibition of RNA polymerase II

Yujing Li,Yunhua Liu,Lu Zhang,Zhuolong Zhou,Jin Wang,Guanglong Jiang,Bin He,Kevin Van Der Jeught,Xiaoming He,Guang Ji,Michael Frieden,Lifei Wang,Yunlong Liu,Milan Radovich,Yunzhang Fang ,Hanchen Xu,Bryan P Schneider,Zhenhua Luo,Yibin Deng,Xinna Zhang,Kun Huang,Xiongbin Lu

doi:10.1038/s41467-018-06811-z

Abstract

Heterozygous deletion of chromosome 17p (17p) is one of the most frequent genomic events in human cancers. Beyond the tumor suppressor TP53, the POLR2A gene encoding the catalytic subunit of RNA polymerase II (RNAP2) is also included in a ~20-megabase deletion region of 17p in 63% of metastatic castration-resistant prostate cancer (CRPC). Using a focused CRISPR-Cas9 screen, we discovered that heterozygous loss of 17p confers a selective dependence of CRPC cells on the ubiquitin E3 ligase Ring-Box 1 (RBX1). RBX1 activates POLR2A by the K63-linked ubiquitination and thus elevates the RNAP2-mediated mRNA synthesis. Combined inhibition of RNAP2 and RBX1 profoundly suppress the growth of CRPC in a synergistic manner, which potentiates the therapeutic effectivity of the RNAP2 inhibitor, α-amanitin-based antibody drug conjugate (ADC). Given the limited therapeutic options for CRPC, our findings identify RBX1 as a potentially therapeutic target for treating human CRPC harboring heterozygous deletion of 17p.

Highlights

Heterozygous deletion of chromosome 17p (17p) is one of the most frequent genomic events in human cancers
The comprehensive analysis of prostate cancer genomes revealed that the TP53 deletion is often included in a large fragment deletion that spans over almost the whole short arm of chromosome 17 (17p) (Fig. 1b)
We found that Ring-Box 1 (RBX1) knockdown, indicated by red fluorescence protein (RFP) levels co-expressed with RBX1 small hairpin RNA (shRNA), impaired the global transcription in both 17ploss cells and 17pneutral cells (Fig. 6a and Supplementary Fig. 5a)

Summary

Introduction

Heterozygous deletion of chromosome 17p (17p) is one of the most frequent genomic events in human cancers. Beyond the tumor suppressor TP53, the POLR2A gene encoding the catalytic subunit of RNA polymerase II (RNAP2) is included in a ~20-megabase deletion region of 17p in 63% of metastatic castration-resistant prostate cancer (CRPC). Given the limited therapeutic options for CRPC, our findings identify RBX1 as a potentially therapeutic target for treating human CRPC harboring heterozygous deletion of 17p. While certain prostate cancer alterations or signatures have prognostic clinical significance, the therapeutic approach targeting those genomic events has not yet been developed It has been long known from cytogenetic and loss of heterozygosity (LOH) studies that deletions on the 17p frequently occur in many types of human cancer[15,16,17]. Using a CRISPR-Cas[9] screen, we uncover that heterozygous deletion of 17p confers a selective dependence on RBX1, inhibition of which had a synergistic and robust suppression in the growth of CRPC along with the treatment of α-amanitinconjugated anti-EpCAM antibodies

Methods

Results

Conclusion