FIGURE 1.

Recognition of miRNAs by TLRs in tumor cells. miRNAs of tumor cells, such as miR-21 and miR-29a, can be packaged into exosomes and secreted to the extracellular environment. Exosomes can transfer these miRNAs to recipient macrophages and eventually reach endosomes, in which miR-21 and miR-29a are recognized by endosomally expressed human TLR8 (or murine TLR7). After the ligation of TLR8 (or TLR7), the adaptor molecule MyD88 is recruited and drives the production of proinflammatory cytokines such as TNF-α and IL-6. This pathway may ultimately lead to tumor growth and metastasis.