Mechanical control of breast cancer malignancy by promotion of mevalonate pathway enzyme synthesis

In breast cancer, mechanotransduction from stiffened extracellular matrix (ECM) drives proliferation and invasion. Here, we use a model of matrix stiffening mimicking progression of breast ductal carcinoma in situ to invasive ductal carcinoma. Quantitative mass spectrometry identified enrichment of ECM-stiffness upregulated mevalonate pathway enzymes, indicating sterol/isoprenoid metabolism reprogramming. Consistently, the first committed mevalonate pathway enzyme, Hydroxymethylglutaryl-CoA Synthase (HMGCS1), was upregulated in human breast cancer specimens and spatially correlated with cross-linked ECM. ECM-stiffness promoted HMGCS1 protein synthesis without corresponding mRNA level alterations, indicating post-transcriptional regulation of mevalonate biosynthesis via microenvironmental mechanical cues to impose rapid metabolic alterations. Moreover, HMGCS1-RNAi blocked the stiffness-driven breast cancer proliferative and invasive phenotype. Mechanistically, mechanotransduction signaling, through integrin and Rac1 to promote HMGCS1 protein expression, drives the breast cancer malignant phenotype. Intriguingly, the Rac1-P29S cancer mutant promoted a malignant phenotype without stiff ECM in a mevalonate-dependent manner. In summary, we define a mechano-responsive pathway controlling mevalonate pathway enzyme synthesis that drives breast cancer malignant behaviors.