MLC1 and breast cancer: Considering that hypoxia may stimulate breast cancer cells toward invasive features as cell motility, formation of stress fibers and matrix contraction [54], the CM from MDA-MB-231 cells exposed to hypoxia promoted in CAFs the phosphorylation of myosin light chain (MLC) on serine-19 (pMLCS19) (Fig. 8c), which is known to be required for the coordination of the actin-myosin contractility [55].