ABCC1 and gastric cancer: MSC-exosomes incorporate into the gastric cancer cells, stimulating the activation of CaM-Ks (predominantly CaM-KII and CaM-KIV), triggering downstream Raf/MEK/ERK signaling cascade activation, which consequently upregulates the expression of multi-drug resistance associated proteins including MDR, MRP, and LRP, eventually conferring chemoresistance in gastric cancer (Ji et al., 2015).