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Chemotherapy represents a major type of clinical treatment against colorectal cancer (CRC). Aberrant drug efflux mediated by transporters acts as a key approach for tumor cells to acquire chemotherapy resistance. Increasing evidence implies that tumor-associated macrophages (TAMs) play a pivotal role in both tumorigenesis and drug resistance. Nevertheless, the specific mechanism through which TAMs regulate drug efflux remains elusive. Here, we discovered that TAMs endow CRC cells with resistance to 5-fluorouracil (5-FU) treatment via a cell-cell interaction-mediated MRP1-dependent drug efflux process. Mechanistically, TAM-secreted C-C motif chemokine ligand 17 (CCL17) and CCL22, via membrane receptor CCR4, activated the PI3K/AKT pathway in CRC tumor cells. Specifically, phosphorylation of AKT inactivated IP3R and induced calcium aggregation in the ER, resulting in the activation of ATF6 and upregulation of GRP78. Accordingly, excessive GRP78 can interact with MRP1 and promote its translocation to the cell membrane, causing TAM-induced 5-FU efflux. Taken together, our results demonstrated that TAMs promote CRC chemotherapy resistance via elevating the expression of GRP78 to promote the membrane translocation of MRP1 and drug efflux, providing direct proof for TAM-induced drug resistance.
Zhang et al. (Fri,) studied this question.