Loss of Insulin Receptor Substrates 1 and 2 Suppresses Kras-Driven Non-Small Cell Lung Cancer

Abstract

Lung cancer remains the leading cause of cancer death worldwide, with non-small cell lung cancer (NSCLC) being the majority of diagnosed cases of lung cancer. Mutant KRAS is found in about 25% of all NSCLC and has proved to be extraordinarily difficult to directly target for therapeutic purposes. It has been demonstrated that mutant KRAS directly binds to and activates PI3K, and this interaction is required for the initiation and maintenance of NSCLC in mice. However, it has remained controversial whether signaling from upstream insulin receptor (IR) and insulin-like growth factor 1 receptor (IGF-1R) contributes to tumorigenesis in the context of activated KRAS, and whether the upstream signaling represents a potential strategy for therapeutic targeting. Using a conditional mouse model of lung tumorigenesis driven by activated Kras and loss of tumor suppressor p53, I have demonstrated that concomitant lung-specific genetic ablation of insulin receptor substrates 1 and 2 (Irs1 and Irs2), which mediate signaling from IR and IGF-1R, inhibits Kras-driven tumor development and significantly extends the survival of mice. However, mice eventually overcome the loss of Irs1 and Irs2 and succumb to lung cancer with a varied but significantly longer latency. Through proteomic characterizations of mouse cell lines established from these tumors, I discovered that tumor cells with loss of Irs1 and Irs2 demonstrate severely suppressed Akt and downstream effector signaling. Metabolic profiling also revealed that loss of Irs1 and Irs2 results in dramatically decreased levels of intracellular amino acids. Similar signaling and metabolic alterations were found in human KRAS-mutant NSCLC cells with double knockout or double knockdown of IRS1 and IRS2, accompanied by enhanced basal autophagy and sensitivity to autophagy and proteasome inhibitors. Acute pharmacological inhibition of IR/IGF-1R signaling in both murine and human KRAS-mutant lung cancer cells also results in decreased intracellular amino acid levels and increased basal autophagy. Therefore, my research demonstrated that Irs1 and Irs2-mediated IR/IGF-1R signaling is essential to KRAS-driven lung tumorigenesis. More importantly, these studies identified amino acid metabolism as a vulnerability in cells that overcome IR/IGF-1R inhibition. Consequently, combinatorial targeting of IR/IGF-1R with autophagy or proteasome inhibitors may represent a viable therapeutic strategy in KRAS-mutant NSCLC.