MicroRNA-155 governs SHIP-1 expression and localization in NK cells and regulates subsequent infiltration into murine AT3 mammary carcinoma.

NK cell migration and activation are crucial elements of tumor immune surveillance. In mammary carcinomas, the number and function of NK cells is diminished, despite being positively associated with clinical outcome. MicroRNA-155 (miR-155) has been shown to be an important regulator of NK cell activation through its interaction with SHIP-1 downstream of inhibitory NK receptor signaling, but has not been explored in regard to NK cell migration. Here, we explored the migratory potential and function of NK cells in subcutaneous AT3 in mice lacking miR-155. Without tumor, these bic/miR-155-/- mice possess similar numbers of NK cells that exhibit comparable surface levels of cytotoxic receptors as NK cells from wild-type (WT) mice. Isolated miR-155-/- NK cells also exhibit equivalent cytotoxicity towards tumor targets in vitro compared to isolated WT control NK cells, despite overexpression of known miR-155 gene targets. NK cells isolated from miR-155-/- mice exhibit impaired F-actin polymerization and migratory capacity in Boyden-chamber assays in response chemokine (C-C motif) ligand 2 (CCL2). This migratory capacity could be normalized in the presence of SHIP-1 inhibitors. Of note, miR-155-/- mice challenged with mammary carcinomas exhibited heightened tumor burden which correlated with a lower number of tumor-infiltrating NK1.1+ cells. Our results support a novel, physiological role for SHIP-1 in the control of NK cell tumor trafficking, and implicate miR-155 in the regulation of NK cell chemotaxis, in the context of mammary carcinoma. This may implicate dysfunctional NK cells in the lack of tumor clearance in mice.