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

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.

Proteasome ubiquitin receptor PSMD4 is an amplification target in breast cancer and may predict sensitivity to PARPi

“…Proteasome function is required for DNA damage response and it has recently been shown that defects in ubiquitin effect response of breast cancer cells to PARP inhibition . Therefore, we investigated the proteasome ubiquitin receptor PSMD4 as a candidate driver of the 1q21 amplicon that is lost in the resistant line.…”

“…Recently it has been shown that PARP1 sensitivity is dependent on proteasome function. [11][12][13] Using siRNA, we knocked down PSMD4 protein in cell lines with amplification of PSMD4 (MCF7 and HCC1187) and show by western blot that this results not only in knock-down of PSMD4, but also the subsequent down-regulation of PARP1 ( Figure 5).…”

“…Proteasome function is required for DNA damage response and it has recently been shown that defects in ubiquitin effect response of breast cancer cells to PARP inhibition. [11][12][13] Therefore, we investigated the proteasome ubiquitin receptor PSMD4 as a candidate driver of the Figure 1B). Thus loss of PSMD4 may be a mechanism for down-regulation of PARP1 protein since array CGH shows the PARP1 gene mapping to chromosome 1q42 is not altered in the resistant line ( Figure 1A).…”

“…Proteasome function is required for DNA damage response and it has recently been shown that defects in ubiquitin affect response of breast cancer cells to PARP inhibition. [11][12][13] In this study, we explore this recent connection between the DNA repair gene PARP1 and the ubiquitin proteasome receptor PSMD4 as it relates to breast cancer oncogenesis, and PARP inhibitor sensitivity and resistance.…”

Strictly Approximating Attributes of DNA Lesion Repair in Terms of Inherent DNA Responses to Mutability and Malignant Transformation

“…Performance dynamics of repair of DNA damage is hence the central attribute to system susceptibility to an integral DNA damage that is rendered prototypically a systematic exposure for further mutability. Defects in the ubiquitin machinery potentially influence response of neoplastic cells to PARP inhibitors, via defective homologous recombination DNA repair [20].…”