Immediate early gene X-1 (IEX-1) modulates apoptosis, cellular growth, mechanical strain-induced cardiac hypertrophy, and vascular intimal hyperplasia. To determine how IEX-1 alters apoptosis, we performed yeast two-hybrid studies using IEX-1 as the "bait" protein, and examined interactions between IEX-1 and proteins expressed by a human kidney cDNA expression library. We found that IEX-1 interacts with several proteins of which at least four are known to play a role in the regulation of apoptosis: (1) calcium-modulating cyclophilin ligand; (2) tumor necrosis factor-related apoptosis-inducing ligand (tumor necrosis factor superfamily, member 10); (3) ML-1 myeloid cell leukemia gene encoded protein; and (4) BAT3, a gene present in the major histo-compatibility complex. Our data suggest that IEX-1 may regulate apoptosis by directly interacting with various proteins involved in the control of apoptotic pathways. (C) 2004 Elsevier Inc. All rights reserved.