Cytokines that are related to ciliary neurotrophic factor (CNTF) are physiologically important survival factors for motoneurons, but the mechanisms by which they prevent neuronal cell death remain unknown. Reg-2/PAP I (pancreatitis-associated protein I), referred to here as Reg-2, is a secreted protein whose expression in motoneurons during development is dependent on cytokines. Here we show that CNTF-related cytokines induce Reg-2 expression in cultured motoneurons. Purified Reg-2 can itself act as an autocrine/paracrine neurotrophic factor for a subpopulation of motoneurons, by stimulating a survival pathway involving phosphatidylinositol-3-kinase, Akt kinase and NF-kappaB. Blocking Reg-2 expression in motoneurons using Reg-2 antisense adenovirus specifically abrogates the survival effect of CNTF on cultured motoneurons, indicating that Reg-2 expression is a necessary step in the CNTF survival pathway. Reg-2 shows a unique pattern of expression in late embryonic spinal cord: it is progressively upregulated in individual motoneurons on a cell-by-cell basis, indicating that only a fraction of motoneurons in a given motor pool may be exposed to cytokines. Thus, Reg-2 is a neurotrophic factor for motoneurons, and is itself an obligatory intermediate in the survival signalling pathway of CNTF-related cytokines.