Magnaporthe Rab5 homologs show distinct functions in nerve growth factor (NGF)-mediated neurite outgrowth and cell differentiation

Nerve growth factor (NGF) binds to TrkA and forms a NGF/TrkA complex at the cell surface, which is then internalized into signaling endosomes and promotes neuronal survival and neurite outgrowth. The small GTPase Rab5 is reported to localize on the plasma membrane and early endosomes, regulating endosome fusion. It was reported that endogenous Rab5 function may need to be suppressed during NGF-induced neurite outgrowth and cell differentiation. Two Rab5 homologs (MoRab5A: MGG_06241 and MoRab5B:MGG_01185) were characterized from the rice blast fungus Magnaporthe oryzae, and MoRab5B was identified as the Rab5 ortholog promoting early endosomal fusion, while MoRab5A specialized to perform a non-redundant function in endosomal sorting. In this study, we examined whether MoRab5A and MoRab5B play different roles in NGF-induced neurite outgrowth and cell differentiation in PC12 cells (a rat pheochromocytoma cell line). Our data showed that MoRab5B is a negative regulator of NGF signaling and neurite outgrowth in PC12 cells, similar to human Rab5 (hRab5). MoRab5B:WT inhibits NGF signaling-dependent neurite outgrowth while the dominant-negative MoRab5B mutant (MoRab5B:DN) enhances NGF signaling and neurite outgrowth. In contrast, MoRab5A:WT and MoRab5A:DN both significantly promote NGF-induced neurite outgrowth, indicating that MoRab5B is more similar to hRab5 than MoRab5A in the regulation of NGF signal transduction.