Induces apoptosis of alpha and beta cells in a dose- and time-dependent manner. Present in insulin secretory granules and likely cosecreted with insulin. Localized in discrete vesicular and perinuclear structure. Highly expressed in the pancreas. Also found in the colon, kidney, prostate, small intestine and testis. 2 N-termini have been observed in the mature protein: the first at Glu-30, resulting from signal peptide cleavage, the second at Ser-46. O-glycosylated. Belongs to the FAM3 family.