Met-signaling controls Dendritic Cell migration by regulating podosome formation and function

Signaling by the HGF receptor/Met in skin-resident Langerhans cells (LC) and dermal dendritic cells (dDC) is essential for their emigration toward draining lymph nodes upon inflammation-induced activation. Here we addressed the role of Met-signaling in distinct steps of LC/dDC emigration from skin by employing a conditional Met-deficient mouse model (Metflox/flox). We found that Met deficiency severely impaired podosome formation in DC and concomitantly decreased proteolytic degradation of gelatin. Accordingly, Met-deficient LC failed to efficiently cross the extracellular matrix (ECM) rich basement membrane between epidermis and dermis. We further observed that Met-signaling by HGF reduced adhesion of bone marrow-derived LC to various ECM factors and enhanced the motility of Met-signaling competent DC in a 3D collagen matrix, which was not the case for Met-deficient LC/DC. We found no impact of Met-signaling on the integrin-independent amoeboid migration of DC in response to the CCR7 chemokine CCL19. Collectively, our data show that the Met-signaling pathway regulates the migratory properties of DC in HGF-dependent and HGF-independent manners.