Release of TNF-α from macrophages is mediated by small GTPase Rab37

Activated macrophages at wound sites release many cytokines which positively affect skin wound healing. However, the molecular mechanisms controlling cytokine secretion from macrophages have not been elucidated. In the present study, we performed an RT-PCR analysis and found that 19 small GTPase Rab isoforms were expressed at skin wound sites, with six of them (i.e. Rab3B, Rab27B, Rab30, Rab33A, Rab37, and Rab40C) being upregulated during the inflammation and proliferation/migration phase of skin repair. We also found that gene expression of Rab37 in murine primary and RAW264.7 macrophages was significantly induced after stimulation with LPS. Overexpression of wild type and constitutively active Rab37 in RAW264.7 cells significantly increased TNF-α secretion, whereas knockdown of Rab37 by siRNA significantly decreased it. We also identified 29 putative Rab37-interacting proteins, including the membrane fusion regulating Munc13-1, using liquid chromatography/linear ion trap mass spectrometry (LC-MS/MS). Immunocytochemical analysis further revealed that TNF-α-containing vesicles were colocalized with both Rab37 and Munc13-1 in activated macrophages. Knockdown of Munc13-1 by siRNA significantly decreased TNF-α secretion. Taken together, these findings demonstrate that Rab37 interacts with Munc13-1 to control TNF-α secretion from activated macrophages.