14,15-EET induces the infiltration and tumor-promoting function of neutrophils to trigger the growth of minimal dormant metastases

Infiltrating neutrophils are known to promote in thedevelopment of tumor. However, it is unclear whether and how neutrophils areinvolved in triggering the growth of dormant metastases. Here we show that14,15-epoxyeicosatrienoic acid (14,15-EET) can trigger the growth of dormantmicrometastases by inducing neutrophilic infiltration and converting neutrophilfunction. 14,15-EET triggered neutrophil infiltration in metastatic lesions byactivating STAT3 and JNK pathways to induce the expression of human IL-8 andmurine CXCL15 in corresponding tumor cells. The continuous expression ofhIL-8/mCXCL15 was maintained by the sustained and enhanced activation of JNKpathway. 14,15-EET up-regulated miR-155 expression by activating STAT3 and JNKpathways. miR-155 in turn down-regulated the expression of SHIP1 and DET1, thusaugmenting the activation of JNK and c-Jun. Moreover, the function ofneutrophils was converted from tumor-suppressing to tumor-promoting by14,15-EET in vivo. By inducing the production of G-CSF/IL-6 in vivo, 14,15-EET induced the enhancement of STAT3 activation in neutrophilsto increase MMP-9 expression and decrease TRAIL expression. Neutrophil-derivedMMP-9 was required for 14,15-EET to induce angiogenesis during the growth ofdormant micrometastases. Depleting neutrophils or inhibiting hIL-8/mCXCL15up-regulation resulted in the failure of 14,15-EET to promote the developmentof micrometastases. These findings reveal a mechanism through which theinfiltration and tumor-promoting function of neutrophils could be induced totrigger the growth of dormant metastases, which might be a driving force forthe tumor recurrence based on dormant metastases.