Stress-Inducible Transcription Factor NUPR1 Is Involved in the Inhibitory Effects Exerted by Statins on Insulin Action in ER-Positive Breast Cancer Cells

Obesity is frequently associated with metabolic alterations like hypercholesterolemia and hyperinsulinemia and represents a major risk factor for several diseases, including breast cancer (BC). Insulin signaling, as well as the frequent overexpression of the insulin receptor (IR), play a key role in BC progression. Emerging evidence suggests that the widely prescribed lipid-lowering drugs, named statins, may reduce the risk of recurrence and blunt BC cell proliferation, mainly inhibiting the HMGCR-dependent activation of the mevalonate pathway. In this study, we investigated the effects of simvastatin, atorvastatin and rosuvastatin in BC cells stimulated by insulin. To this end, we used as a BC model system MCF7 cells and naturally immortalized BCAHC-1 cells, which are characterized by high IR-expression levels. Our investigation demonstrates that statins reduce the proliferation and clonogenic capacity of BC cells prompted by insulin treatment. Mechanistically, statins impair the IR-mediated signaling and downregulate the stress-inducible transcription factor NUPR1, a known regulator of cancer progression. Importantly, NUPR1 inhibition blunted the stimulatory action of insulin on BC cells. Consistent with these findings, survival analyses of large cohorts of patients revealed that high levels of NUPR1 are associated with poor BC prognosis. Overall, our results provide novel mechanistic evidence supporting the repositioning of statins in BC, particularly in tumors characterized by elevated IR expression and activity.