Involved in coupling signal transduction and vesicle trafficking to enable polarized secretion and/or membrane deposition of immune effector molecules (PubMed:11254716). Involved in phagophore growth during mitophagy by regulating ATG9A trafficking to mitochondria (By similarity). Isoform 1 is expressed in the brain, is absent from the lung and the bone marrow and is less abundant in the spleen. Isoform 2 is expressed in the spleen, lung, brain and bone marrow. Isoform 3 is expressed in the brain, is absent from the bone marrow and is less abundant in the spleen and lung. By lipopolysaccharide (LPS).