Complementary genetic screens identify the E3 ubiquitin ligase CBLC, as a modifier of PARP inhibitor sensitivity

// Jessica Frankum 1,* , Pavel Moudry 2,* , Rachel Brough 1 , Zdenek Hodny 3 , Alan Ashworth 1 , Jiri Bartek 2,3 and Christopher J. Lord 1 1 The CRUK Gene Function Laboratory and Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, London, UK 2 Danish Cancer Society Research Center, Strandboulevarden, Copenhagen, Denmark 3 Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Videnska, Czech Republic * These authors contributed equally to this work Correspondence to: Christopher J. Lord, email: // Jiri Bartek, email: // Alan Ashworth, email: // Keywords : DNA damage response, ubiquitin-proteasome system, RNA interference screens, PARP inhibitors, CBLC Received : February 03, 2015 Accepted : February 20, 2015 Published : March 18, 2015 Abstract Based on a series of basic, preclinical and clinical studies, the Poly (ADP-ribose) Polymerase 1 (PARP1) inhibitor, olaparib, has recently been approved for use in ovarian cancer patients with BRCA1 or BRCA2 mutations. By identifying novel predictive biomarkers of tumour cell sensitivity to olaparib, it is possible that the utility of PARP inhibitors could be extended beyond this patient subgroup. Many of the known genetic determinants of PARP inhibitor response have key roles in DNA damage response (DDR) pathways. Although protein ubiquitylation is known to play an important role in regulating the DDR, the exact mechanisms by which this occurs are not fully understood. Using two parallel RNA interference-based screening approaches, we identified the E3 ubiquitin ligase, CBLC, as a candidate biomarker of response to olaparib. We validated this observation by demonstrating that silencing of CBLC causes increased sensitivity to olaparib in breast cancer cell line models and that defective homologous recombination (HR) DNA repair is the likely cause. This data provides an example of how defects in the ubiquitin machinery have the potential to influence the response of tumour cells to PARP inhibitors.