ARMER (apoptotic regulator in the membrane of the endoplasmic reticulum), also known as ADP-ribosylation-like factor 6-interacting protein 1 (ARL6IP1 or AIP1), is a multi-pass membrane protein that belongs to the Ras superfamily. It is expressed in brain, thymus, lung, bone marrow and, to a lesser extent, in spleen, kidney and liver. ARMER is not found in the heart and is found predominantly in early myeloid progenitor cells localizing to the intracytoplasmic membranes. It interacts with ARL6, inhibits caspase-9 activity by inhibiting proteolysis of downstream substrates (including LEHD-AFC, vimentin and caspase-3) and is down-regulated during myeloid differentiation. ARMER may play a role in membrane trafficking, protein transport or cell signaling during hematopoietic maturation.