PT - JOURNAL ARTICLE AU - Melanie Rouleau AU - Joannie Roberge AU - Judith Bellemare AU - Chantal Guillemette TI - Dual Roles for Splice Variants of the Glucuronidation Pathway as Regulators of Cellular Metabolism AID - 10.1124/mol.113.089227 DP - 2013 Oct 18 TA - Molecular Pharmacology PG - mol.113.089227 4099 - http://molpharm.aspetjournals.org/content/early/2013/10/18/mol.113.089227.short 4100 - http://molpharm.aspetjournals.org/content/early/2013/10/18/mol.113.089227.full AB - Transcripts of the UGT1A gene, encoding half of human UGT enzymes, undergo alternative splicing, resulting in active enzymes named isoforms 1 (i1s) and novel truncated isoforms 2 (i2s). Here, we investigated the effects of depleting endogenous i2 on drug response and to unveil any additional biological role(s) for the truncated novel UGT proteins. We used an integrated systems biology approach that combines RNA interference with unbiased global genomic and proteomic screens, and used the HT115 colorectal cancer cells as a model. Consistent with previous evidence suggesting that i2s negatively regulate i1s through protein-protein interactions, i2-depleted cells were less sensitive to drug-induced cell death (IC50 of 0.45 ± 0.05 μM vs. 0.22 ± 0.03 μM; P=0.006), demonstrating that modulation of i2 levels meaningfully impacts drug bioavailability and cellular response. We also observed reduced production of reactive oxygen species by 30 % (P<0.05), and an enhanced expression (>1.2 fold; P<0.05) of several proteins such as hemoglobin alpha genes and superoxide dismutase 1 that have network functions associated with antioxidant properties. Interaction proteomics analysis of endogenous proteins from the cellular model, mainly in human intestine but also in kidney tissues further uncovered interactions between i2s (but not i1s) and the antioxidant enzymes catalase and peroxiredoxin 1, which may influence antioxidant potential through sequestration of these novel partners. Our findings demonstrate for the first time dual roles for i2s in the cellular defense system as endogenous regulators of drug response as well as in oxidative stress.