Deficiency of the splicing factor RBM10 limits EGFR inhibitor response in EGFR mutant lung cancer

Molecularly targeted cancer therapy has improved outcomes for cancer patients with targetable oncoproteins, such as mutant epidermal growth factor receptor (EGFR) in lung cancer. Yet, long-term patient survival remains limited because treatment responses are typically incomplete. One potential explanation for the lack of complete and durable responses is that oncogene-driven cancers with activating mutations in the EGFR often harbor additional co-occurring genetic alterations. This hypothesis remains untested for most genetic alterations that co-occur with mutant EGFR. Here, we report the functional impact of inactivating genetic alteration of the mRNA splicing factor RBM10 that co-occur with mutant EGFR. RBM10 deficiency decreased EGFR inhibitor efficacy in patient-derived EGFR mutant tumor models. RBM10 modulated mRNA alternative splicing of the mitochondrial apoptotic regulator Bcl-x to regulate tumor cell apoptosis during treatment. Genetic inactivation of RBM10 diminished EGFR inhibitor-mediated apoptosis by decreasing the ratio of Bcl-xS-(pro-apoptotic)-to-Bcl-xL(anti-apoptotic) Bcl-x isoforms. RBM10 deficiency was a biomarker of poor response to EGFR inhibitor treatment in clinical samples. Co-inhibition of Bcl-xL and mutant EGFR overcame resistance induced by RBM10 deficiency. This study sheds light on the role of co-occurring genetic alterations, and on the impact of splicing factor deficiency in the modulation of sensitivity to targeted kinase inhibitor cancer therapy.