Insulin Receptor Loss Impairs Mammary Tumorigenesis in Mice

Breast cancer (BC) prognosis and outcome are adversely affected by increased body weight, obesity and the obesity-associated type 2 diabetes. Hyperinsulinemia, which is commonly seen as part of metabolic reprograming in the obese state, has been associated with higher risk of death and recurrence in BC. Up to 80% of breast cancers overexpress the insulin receptor (INSR) de novo, which correlates with worse prognosis. To directly probe the role of insulin signaling in mammary tumorigenesis in the mouse, we generated the MMTV-driven polyoma middle T (PyMT) and ErbB2/Her2 BC models, respectively, with coordinate mammary epithelium-restricted deletion of the INSR. In both models, deletion of either one or both copies of the INSR in the mammary gland led to a marked delay in tumor onset and burden, including in mice fed to mimic conditions of human obesity. Longitudinal monitoring of generated mouse models revealed that tumor initiation, rather than progression and metastasis, were impacted by INSR deletion. The similarity of phenotypes elicited by the deletion of one or both copies of INSR raises the possibility that there is a dose-dependent threshold for the contribution of INSR to mammary tumorigenesis.