Glutathione transferases are a multigene family of proteins that catalyze the conjugation of toxic electrophiles and carcinogens to glutathione. Glutathione transferase Pi (GSTP) is commonly overexpressed in human tumors and there is emerging evidence that the enzyme has additional cellular functions in addition to its role in drug and carcinogen detoxification. To investigate the unique functions of this enzyme, we have crossed Gstp null mice with an initiated model of colon cancer, the Apc Min mouse. In contrast to the Apc Min/؉ Gstp1/p2 ؉/؉ (Gstp-wt Apc Min ) mice, which rarely develop colonic tumours, Apc Min/؉ Gstp1/p2 ؊/؊ (Gstp-null Apc Min ) mice had a 6-fold increase in colon adenoma incidence, and a 50-fold increase in colorectal adenoma multiplicity, relative to Gstp-wt Apc Min . This increase was associated with early tumor onset and decreased survival. Analysis of the biochemical changes in the colon tissue of Gstp-null Apc Min mice demonstrated a marked induction of many inflammatory genes, including IL-6, IL-4, IFN-␥, and inducible nitric oxide synthase. In support of the induction of inducible nitric oxide synthase, a profound induction of nitrotyrosine adducts was observed. Gstp therefore appears to play a role in controlling inflammatory responses in the colon, which would explain the change in tumor incidence observed. These data also suggest that individual variation in GSTP levels may be a factor in colon cancer susceptibility.cancer ͉ colorectal ͉ inflammation G lutathione S-transferases play a key role in chemical detoxification by catalyzing the conjugation of reduced glutathione to reactive electrophiles (1). In a genetic approach to study GST functions, we have generated mice nulled at the glutathione transferase Pi (GSTP) Gstp gene locus (2). These mice develop normally, are fertile, and show no obvious abnormalities. Topical application of the tumor initiator 7,12-dimethylbenz[a]anthracene, followed by the promoting agent 12-0-tetradecanoylphorbol-13-acetate, resulted in a significant increase in the number of papillomas in null animals (2). Similarly, increased adenoma formation in the lungs of Gstp-null mice relative to wild-type mice was also observed following dosing with benzo[a]pyrene, 3-methylcholanthene and urethane (3). In recent studies we have obtained evidence that this protein can also modulate toxicological or carcinogenic response in a manner distinct from its role in chemical detoxification (4). Further evidence of unique GSTP function is demonstrated by its ability to form protein-protein interactions and regulate the activities of several cellular proteins (JNK and TRAF2) independently of its catalytic function (5, 6). GSTP has also been shown to potentiate S-glutathionylation reactions following oxidative and nitrosative stress in vitro and in vivo (7).To further evaluate the role of GSTP in disease processes, we have investigated whether GSTP can alter colon cancer susceptibility in the Apc Min mouse. Mutations in the Apc gene is a major initiating factor in the aet...