Silencing vimentin expression decreases pulmonary metastases in a pre-diabetic mouse model of mammary tumor progression

Increased breast cancer risk and mortality has been associated with obesity and type 2 diabetes (T2D). Hyperinsulinemia, a key factor in obesity, pre-diabetes and T2D, has been associated with decreased breast cancer survival. In this study, a mouse model of pre-diabetes (MKR mouse) was used to investigate the mechanisms through which endogenous hyperinsulinemia promotes mammary tumor metastases. The MKR mice developed larger primary tumors and greater number of pulmonary metastases compared with wild-type (WT) mice after injection with c-Myc/Vegf overexpressing MVT-1 cells. Analysis of the primary tumors showed significant increase in vimentin protein expression in the MKR mice compared with WT. We hypothesized that vimentin was an important mediator in the effect of hyperinsulinemia on breast cancer metastasis. Lentiviral short hairpin RNA knockdown of vimentin led to a significant decrease in invasion of the MVT-1 cells and abrogated the increase in cell invasion in response to insulin. In the pre-diabetic MKR mouse, vimentin knockdown led to a decrease in pulmonary metastases. In vitro, we found that insulin increased pAKT, prevented caspase 3 activation, and increased vimentin. Inhibiting the phosphatidylinositol 3 kinase/AKT pathway, using NVP-BKM120, increased active caspase 3 and decreased vimentin levels. This study is the first to show that vimentin has an important role in tumor metastasis in vivo in the setting of pre-diabetes and endogenous hyperinsulinemia. Vimentin targeting may be an important therapeutic strategy to reduce metastases in patients with obesity, pre-diabetes or T2D.