Posttranscriptional Regulation of PARG mRNA by HuR Facilitates DNA Repair and Resistance to PARP Inhibitors

Cancer Res. 2017 Sep 15;77(18):5011-5025. doi: 10.1158/0008-5472.CAN-16-2704. Epub 2017 Jul 7.

Abstract

The majority of pancreatic ductal adenocarcinomas (PDAC) rely on the mRNA stability factor HuR (ELAV-L1) to drive cancer growth and progression. Here, we show that CRISPR-Cas9-mediated silencing of the HuR locus increases the relative sensitivity of PDAC cells to PARP inhibitors (PARPi). PDAC cells treated with PARPi stimulated translocation of HuR from the nucleus to the cytoplasm, specifically promoting stabilization of a new target, poly (ADP-ribose) glycohydrolase (PARG) mRNA, by binding a unique sequence embedded in its 3' untranslated region. HuR-dependent upregulation of PARG expression facilitated DNA repair via hydrolysis of polyADP-ribose on related repair proteins. Accordingly, strategies to inhibit HuR directly promoted DNA damage accumulation, inefficient PAR removal, and persistent PARP-1 residency on chromatin (PARP-1 trapping). Immunoprecipitation assays demonstrated that the PARP-1 protein binds and posttranslationally modifies HuR in PARPi-treated PDAC cells. In a mouse xenograft model of human PDAC, PARPi monotherapy combined with targeted silencing of HuR significantly reduced tumor growth compared with PARPi therapy alone. Our results highlight the HuR-PARG axis as an opportunity to enhance PARPi-based therapies. Cancer Res; 77(18); 5011-25. ©2017 AACR.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Apoptosis
  • Biomarkers, Tumor / genetics
  • Biomarkers, Tumor / metabolism
  • Carcinoma, Pancreatic Ductal / genetics
  • Carcinoma, Pancreatic Ductal / metabolism
  • Carcinoma, Pancreatic Ductal / pathology
  • Cell Nucleus / drug effects
  • Cell Nucleus / genetics
  • Cell Proliferation
  • DNA Damage / drug effects
  • DNA Damage / genetics
  • DNA Repair / drug effects
  • DNA Repair / genetics*
  • Drug Resistance, Neoplasm / genetics*
  • ELAV-Like Protein 1 / antagonists & inhibitors
  • ELAV-Like Protein 1 / genetics
  • ELAV-Like Protein 1 / metabolism*
  • Female
  • Glycoside Hydrolases / genetics*
  • Humans
  • Mice
  • Mice, Nude
  • Pancreatic Neoplasms / genetics
  • Pancreatic Neoplasms / metabolism
  • Pancreatic Neoplasms / pathology
  • Poly(ADP-ribose) Polymerase Inhibitors / pharmacology*
  • Poly(ADP-ribose) Polymerases / chemistry*
  • RNA Processing, Post-Transcriptional*
  • RNA, Messenger / genetics*
  • Tumor Cells, Cultured
  • Up-Regulation
  • Xenograft Model Antitumor Assays

Substances

  • Biomarkers, Tumor
  • ELAV-Like Protein 1
  • ELAVL1 protein, human
  • Poly(ADP-ribose) Polymerase Inhibitors
  • RNA, Messenger
  • Poly(ADP-ribose) Polymerases
  • Glycoside Hydrolases
  • poly ADP-ribose glycohydrolase

Supplementary concepts

  • Pancreatic Carcinoma