Endophilin B1: Guarding the gate to destruction.

Endophilin B1 is a member of the endophilin family that is localized predominantly to intracellular membranes. Also known as Bax-interacting factor-1 (Bif-1), this protein has been observed to regulate the membrane dynamics of various intracellular compartments, such as the control of mitochondrial morphology and autophagosome formation in fibroblast. Endophilin B1 is expressed in the brain, but its functions in neurons had remained unknown. Recently, we have observed a novel role of endophilin B1 in neurons where it controls the trafficking of TrkA, cognate receptor for the prototypic neurotrophin nerve growth factor (NGF). Knock-down of endophilin B1 expression induces precocious targeting of NGF/TrkA to late endosomes and lysosomes, thereby leading to reduced TrkA levels. This is accompanied by marked attenuation of NGF-induced gene transcription and neurite outgrowth. Our observations suggest that endophilin B1 regulates TrkA level and downstream functions by controlling the movement of TrkA to late endosomes/lysosomes, possibly acting at the level of early endosomes.