Carcinogen-induced skin tumor development requires leukocytic expression of the transcription factor Runx3.

Carcinogen-induced skin tumorigenesis depends heavily on proinflammatory tumor-promoting processes. Here, we show that leukocytic Runx3 expression is central to the two-stage DMBA/TPA-induced skin tumorigenesis. Runx3-null mice were highly resistant to this process and concomitant ablation of Runx3 in dendritic and T cells fully recapitulated this resistance. Mechanistically, this resistance was associated with a shift in the skin cytokine milieu toward a tumor nonpermissive microenvironment. Specifically, leukocytic Runx3 loss substantially increased the antitumorigenic cytokine thymic stromal lymphopoietin (TSLP) and profoundly decreased two protumorigenic cytokines, interleukin-17a and osteopontin. Therefore, inflammation-mediated tumor promotion requires leukocytic Runx3 expression, as its loss creates a unique cytokine composition that polarizes the tumor microenvironment to a potent antitumorigenic state.