Functional significance of co-occurring mutations in and in breast cancer.

The PI3Kα signaling pathway is frequently hyper-activated in breast cancer (BrCa), as a result of mutations/amplifications in oncogenes (e.g. ), decreased function in tumor suppressors (e.g. ) or activating mutations in key components of the pathway. In particular, activating mutations of (45%) are frequently found in luminal A BrCa samples. Genomic studies have uncovered inactivating mutations in (13-20%) and (8%), two upstream kinases of the JNK apoptotic pathway in luminal A BrCa samples. Further, simultaneous mutation of and are found in 11% of mutant tumors. How these two alterations may cooperate to elicit tumorigenesis and impact the sensitivity to PI3K and AKT inhibitors is currently unknown. Using CRISPR gene editing we have genetically disrupted expression in mutant cell lines to specifically create models reflecting the mutational status of and in BrCa patients. deficient cell lines exhibited ~2.4-fold increased proliferation rate and decreased sensitivity to PI3Kα/δ(AZD8835) and AKT (AZD5363) inhibitors (2.61 and ~5.23-fold IC increases, respectively) compared with parental control cell lines. In addition, mechanistic analysis revealed that disruption enhances AKT phosphorylation and downstream signaling and reduces sensitivity to AZD5363-mediated pathway inhibition. This appears to be a consequence of deficient MAP3K1-JNK signaling increasing IRS1 stability and therefore promoting IRS1 binding to p85, resulting in enhanced PI3Kα activity. Using 3D-MCF10A-PI3Kα models, we found that MAP3K1 depletion increased overall acinar volume and counteracted AZD5363-mediated reduction of acinar growth due to enhanced proliferation and reduced apoptosis. Furthermore, efficacy studies revealed that MAP3K1-deficient MCF7 tumors were less sensitive to AKT inhibitor treatment, compared with parental MCF7 tumors. Our study provides mechanistic and evidence indicating a role for as a tumor suppressor gene at least in the context of -mutant backgrounds. Further, our work predicts that mutational status may be considered as a predictive biomarker for efficacy in PI3K pathway inhibitor trials.