p16(INK4a), is a multiple tumor suppressor, playing an important role in proliferation and tumorigenesis. To screen the p16(INK4a) -associated proteins, we performed a yeast two-hybrid assay and identified a novel protein isochorismatase domain containing 2 (ISOC2). ISOC2 conserves in different species, and encodes 205 and 210 amino acids in human and mouse, respectively. The expression of ISOC2 in mouse is universal but predominantly in uterus, stomach, and urinary tract system. Interaction between ISOC2 and p16(INK4a) was verified using in vitro pull-down assays and in vivo co-immunoprecipitation. Confocal microscopy studies using green and cyan fluorescent fusion proteins determined that ISOC2 co-localizes with p16(INK4a). Over-expressed ISOC2 is able to inhibit p16(INK4a) in dose-dependent manner. Our data indicated that ISOC2 is a novel functional protein, which is able to bind and co-localize with a tumor suppressor INK4, INK4, gene p16(INK4a). Over-expressed ISOC2 inhibits the expression of p16(INK4a), suggesting that this novel gene may play a role during the INK4a tumor development by interacting with p16(INK4a). (c) 2007 Elsevier Inc. All rights reserved.