Based on previously published observations regarding the protective effects of interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha) against gamma radiation, alkylating agents and ultraviolet radiation, we hypothesized that the protection against such DNA damaging treatments can be the result of a 'stress'-like response induced by these cytokines and mediated by early response cellular gene(s). By applying the mRNA differential display to RNA obtained from A549 lung carcinoma cell line that was incubated with 50 ng/ml IL-1 for 0, 1, 2, and 6 h, we identified several cDNA fragments that correspond to genes regulated by IL-1. The full length cDNA for one fragment was obtained using 5'RACE, cloned, sequenced, and found to be homologous to human A1, a Bcl-2-related gene. In this study, we report that the expression of human A1 is either absent or present at low levels in leukemic cells, while it is expressed in human bone marrow cells and abundant in peripheral blood progenitors. It is induced by IL-1 and TNF alpha in A549 lung carcinoma, bone marrow, and certain leukemic cells. A1 is also induced in leukemic cells during granulocytic or macrophage but not erythroid differentiation. In conclusion, this is the first demonstration that A1 is inducible by cytokines in human bone marrow and certain tumor cells as well as myeloid differentiation in leukemic cells.