NIK regulates MT1-MMP activity and promotes glioma cell invasion independently of the canonical NF-κB pathway

A growing body of evidence implicates the noncanonical NF-kappa B pathway as a key driver of glioma invasiveness and a major factor underlying poor patient prognoses. Here, we show that NF-kappa B-inducing kinase (NIK/MAP3K14), a critical upstream regulator of the noncanonical NF-kappa B pathway, is both necessary and sufficient for cell-intrinsic invasion, as well as invasion induced by the cytokine TWEAK, which is strongly associated with tumor pathogenicity. NIK promotes dramatic alterations in glioma cell morphology that are characterized by extensive membrane branching and elongated pseudopodial protrusions. Correspondingly, NIK increases the phosphorylation, enzymatic activity and pseudopodial localization of membrane type-1 matrix metalloproteinase (MT1-MMP/MMP14), which is associated with enhanced tumor cell invasion of three-dimensional collagen matrices. Moreover, NIK regulates MT1-MMP activity in cells lacking the canonical NF-kappa B p65 and cRel proteins. Finally, increased expression of NIK is associated with elevated MT1-MMP phosphorylation in orthotopic xenografts and co-expression of NIK and MT1-MMP in human tumors is associated with poor glioma patient survival. These data reveal a novel role of NIK to enhance pseudopodia formation, MT1-MMP enzymatic activity and tumor cell invasion independently of p65. Collectively, our findings underscore the therapeutic potential of approaches targeting NIK in highly invasive tumors.