Class 3 semaphorins induce F‐actin reorganization in human dendritic cells: Role in cell migration

Class 3 Sema signal through NRP and plexin coreceptors in human DCs to induce actin reorganization and promote cellular migration. Class 3 semaphorins (Semas) are soluble proteins that are well recognized for their role in guiding axonal migration during neuronal development. In the immune system, Sema3A has been shown to influence murine dendritic cell (DC) migration by signaling through a neuropilin (NRP)‐1/plexin‐A1 coreceptor axis. Potential roles for class 3 Semas in human DCs have yet to be described. We tested the hypothesis that Sema3A, ‐3C, and ‐3F, each with a unique NRP‐1 and/or NRP‐2 binding specificity, influence human DC migration. In this report, we find that although NRP‐1 and NRP‐2 are expressed in human immature DCs (imDCs), NRP‐2 expression increases as cells mature further, whereas expression of NRP‐1 declines dramatically. Elevated levels of RNA encoding plexin‐A1 and ‐A3 are present in both imDCs and mature DC (mDCs), supporting the relevance of Sema/NRP/plexin signaling pathways in these cells. Sema3A, ‐3C, and ‐3F bind to human DCs, with Sema3F binding predominantly through NRP‐2. The binding of these Semas leads to reorganization of actin filaments at the plasma membrane and increased transwell migration in the absence or presence of chemokine CCL19. Microfluidic chamber assays failed to demonstrate consistent changes in speed of Sema3C‐treated DCs, suggesting increased cell deformability as a possible explanation for enhanced transwell migration. Although monocytes express RNA encoding Sema3A, ‐3C, and ‐3F, only RNA encoding Sema3C increases robustly during DC differentiation. These data suggest that Sema3A, ‐3C, and ‐3F, likely with coreceptors NRP‐1, NRP‐2, and plexin‐A1 and/or ‐A3, promote migration and possibly other activities of human DCs during innate and adaptive immune responses.