Abstract 920: COP1 E3 ligase regulates response to oncogenic MAPK pathway inhibition

Oncogenically activated RAS-MAPK pathway is the driver of several cancers including the majority of non-small cell lung adenocarcinomas (NSCLC). RAS-MAPK pathway is activated in NSCLC tumors via diverse genetic alterations in upstream receptor tyrosine kinases such as EGFR and ALK as well as in RAS, BRAF, MEK and RAS GTPase activating protein (GAP) and tumor suppressor, NF1. Molecular targeting of players of RAS-MAPK pathway can elicit an initial tumor response in many patients. However, most patients show an incomplete response and some fail to respond despite the presence of RAS-MAPK pathway activating genetic lesion in the tumor. Hence, it is important to understand the molecular basis of response and resistance to targeted therapies inhibiting the RAS-MAPK pathway in lung adenocarcinomas in order to improve patient survival. We conducted a genetic screen to identify regulators of response to MAPK pathway inhibition in lung adenocarcinomas. Our genetic screen uncovered the E3 ubiquitin ligase COP1/RFWD2 as a novel modulator of response to inhibition of RAS-MAPK pathway. We found that depletion of COP1 and members of its complex, as well as proteasomal subunits, confers resistance to RAS-MAPK pathway inhibition in human lung adenocarcinoma cells with oncogenically activated RAS-MAPK pathway. Interestingly, oncogenic targets of COP1 include MAPK pathway effectors, presence of which has been shown to support the survival of cancer cells with oncogenically activated MAPK upon inhibition of the RAS-MAPK pathway. Hence, we tested if depletion of COP1 alters the levels of those oncogenic substrates. Excitingly, we observed a substantial impact of COP1 depletion on the levels of certain effectors in the presence of RAS-MAPK inhibitors in genetically diverse NSCLC cells and also in oncogenic-BRAF driven melanoma cells. Our studies suggests that depletion of COP1 confers resistance to MAPK pathway inhibition in RAS-MAPK pathway driven cancers through accumulation of specific MAPK pathway effectors. This work has improved our understanding of the molecular basis of tumor cell resilience during initial treatment as well as of primary treatment resistance. Additionally, we are examining if levels of COP1 could be a biomarker for predicting response to RAS-MAPK pathway inhibitor therapy. We will also determine if the resistance-conferring COP1 substrate could be cotargeted along with RAS-MAPK pathway to improve the patient response in RAS-MAPK pathway driven lung ade