The G protein, G(ialpha2), regulates a number of cellular functions including cell migration, proliferation, and differentiation. The transduction of signal depends on the ability of the alpha subunit to cycle between a GDP bound and an active GTP bound state capable of interacting with intracellular enzymes. Here, we now report the novel interaction of gip2 (constitutively activated G(ialpha2)) with the cytoplasmic domain of UNC5H2. Like G(ialpha2), we found that UNC5H2 is widely expressed particularly in cells which migrate. UNC5H2 binds G(ialpha), when it is charged with GTP. The interaction of G(ialpha2) and UNC5H2 liberated adenylyl cyclase from G(ialpha2) inhibition. Thus, by sequestering the alpha subunit, UNC5H2 is a novel inhibitor of G(ialpha2) thereby increasing intracellular cAMP levels. The expression of UNC5H2 in the brain and immune system suggests that this novel inhibitor of G protein signaling may have broad significance for axonal guidance and chemotaxis. (C) 2002 Elsevier Science (USA). All rights reserved.