Crosstalk between tumour and stroma modifies CLIC4 cargo in extracellular vesicles

Mouse models of breast cancer have revealed that tumour‐bearing hosts must express the oxidoreductase CLIC4 to develop lung metastases. In the absence of host CLIC4, primary tumours grow but the lung premetastatic niche is defective for metastatic seeding. Primary breast cancer cells release EVs that incorporate CLIC4 as cargo and circulate in plasma of wildtype tumour‐bearing hosts. CLIC4‐deficient breast cancer cells also form tumours in wildtype hosts and release EVs in plasma, but these EVs lack CLIC4, suggesting that the tumour is the source of the plasma‐derived EVs that carry CLIC4 as cargo. Paradoxically, circulating EVs are also devoid of CLIC4 when CLIC4‐expressing primary tumours are grown in CLIC4 knockout hosts. Thus, the incorporation of CLIC4 (and perhaps other factors) as EV cargo released from tumours involve specific signals from the surrounding stroma determined by its genetic composition. Since CLIC4 is also detected in circulating EVs from human breast cancer patients, future studies will address its association with disease.