May play a role in early endosome fusion upstream of RAB5, hence regulating receptor trafficking and fluid-phase transport (By similarity). Enhances cellular sensitivity to TNF-induced apoptosis. May interact with EEA1. Colocalizes with EEA1 and RAB5 at endosomal membrane fusion hot spots. May translocate to the endoplasmic reticulum in the early phase of apoptosis. Expressed in brain, stomach and thymus, as well as in kidney, spleen, and skeletal muscle. Also expressed in peripheral blood mononuclear cells and dendritic cells. Up-regulated by TNF, bacterial lipopolysaccharides (LPS) and phorbol myristate acetate (PMA) (at protein level). The PH and FYVE domains may be important for TNF-induced localization to the endoplasmic reticulum and for enhanced cellular sensitivity to TNF-induced apoptosis. The FYVE domain is important for binding to the endosomal membrane (By similarity).