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Background Considering previous result in Non-Small Cell Lung Cancer (NSCLC), we investigated in human cancer cells the role of PARP3 in the regulation of telomerase activity. Methods We selected A549 (lung adenocarcinoma cell line) and Saos-2 (osteosarcoma cell line), with high and low telomerase activity levels, respectively. The first one was transfected using a plasmid construction containing a PARP3 sequence, whereas the Saos-2 cells were submitted to shRNA transfection to get PARP3 depletion. PARP3 expression on both cell systems was evaluated by real-time quantitative PCR and PARP3 protein levels, by Western-blot. Telomerase activity was determined by TRAP assay. Results In A549 cells, after PARP3 transient transfection, data obtained indicated that twenty-four hours after transfection, up to 100-fold increased gene expression levels were found in the transfected cells with pcDNA/GW-53/PARP3 in comparison to transfected cells with the empty vector. Moreover, 48 hours post-transfection, telomerase activity decreased around 33%, and around 27%, 96 hours post-transfection. Telomerase activity average ratio was 0.67 ± 0.05, and 0.73 ± 0.06, respectively, with significant differences. In Saos-2 cells, after shRNA-mediated PARP3 silencing, a 2.3-fold increase in telomerase activity was detected in relation to the control. Conclusion Our data indicated that, at least in some cancer cells, repression of PARP3 could be responsible for an increased telomerase activity, this fact contributing to telomere maintenance and, therefore, avoiding genome instability., Fundación de Investigación Médica Mutua Madrileña, Neumomadrid, Banco Santander, Universidad Complutense de Madrid, Red Temática de Investigación Cooperativa en Cáncer, Depto. de Bioquímica y Biología Molecular, Fac. de Farmacia, TRUE, pub

The accurate quantification of the metabolic enzyme UGT2B17 has been hampered by the high sequence identity with other UGT2B enzymes (as high as 94%) and by the lack of a specific antibody. Knowing the significance of the UGT2B17 pathway in drug and hormone metabolism and cancer, we developed a specific monoclonal antibody (EL-2B17mAb), initially validated by the lack of detection in liver microsomes of an individual carrying no UGT2B17 gene copy and in supersomes expressing UGT2B enzymes. Immunohistochemical detection in livers reveals a strong labeling of bile ducts and variable labeling of hepatocytes. Expression levels assessed by immunoblotting were highly correlated to mass spectrometry-based quantification (r = 0.93) and three major expression patterns (absent, low or high) were evidenced. Livers with very low expression were carriers of the functional rs59678213 G variant, which is located in the binding site for the transcription factor Forkhead Box A1 (FOXA1) of the UGT2B17 promoter. The highest expression was observed for individuals carrying at least one rs59678213 A allele. A multiple regression analysis indicated that the number of gene copies explained only 8% of UGT2B17 protein expression, 49% when adding rs59678213 and reached 54% when including sex. The novel EL-2B17mAb antibody allowed specific UGT2B17 quantification and exposed different patterns of hepatic expression. It further suggests that FOXA1 is a key driver of UGT2B17 expression in the liver. The availability of this molecular tool will help characterize UGT2B17 level in various disease states and establish more precisely the UGT2B17 enzyme contribution to drug and hormone metabolism

The accurate quantification of the metabolic enzyme UGT2B17 has been hampered by the high sequence identity with other UGT2B enzymes (as high as 94%) and by the lack of a specific antibody. Knowing the significance of the UGT2B17 pathway in drug and hormone metabolism and cancer, we developed a specific monoclonal antibody (EL-2B17mAb), initially validated by the lack of detection in liver microsomes of an individual carrying no UGT2B17 gene copy and in supersomes expressing UGT2B enzymes. Immunohistochemical detection in livers reveals a strong labeling of bile ducts and variable labeling of hepatocytes. Expression levels assessed by immunoblotting were highly correlated to mass spectrometry-based quantification (r = 0.93) and three major expression patterns (absent, low or high) were evidenced. Livers with very low expression were carriers of the functional rs59678213 G variant, which is located in the binding site for the transcription factor Forkhead Box A1 (FOXA1) of the UGT2B17 promoter. The highest expression was observed for individuals carrying at least one rs59678213 A allele. A multiple regression analysis indicated that the number of gene copies explained only 8% of UGT2B17 protein expression, 49% when adding rs59678213 and reached 54% when including sex. The novel EL-2B17mAb antibody allowed specific UGT2B17 quantification and exposed different patterns of hepatic expression. It further suggests that FOXA1 is a key driver of UGT2B17 expression in the liver. The availability of this molecular tool will help characterize UGT2B17 level in various disease states and establish more precisely the UGT2B17 enzyme contribution to drug and hormone metabolism

The detoxification enzyme UDP-glucuronosyltransferase UGT2B10 is specialized in the N-linked glucuronidation of many drugs and xenobiotics. Preferred substrates possess tertiary aliphatic amines and heterocyclic amines such as tobacco carcinogens and several anti-depressants and anti-psychotics. We hypothesized that alternative splicing (AS) constitutes a mean to regulate steady state levels of UGT2B10 and enzyme activity. We established the transcriptome of UGT2B10 in normal and tumoral tissues of multiple individuals. Highest expression was in the liver, where ten AS transcripts represented 50% of the UGT2B10 transcriptome in 50 normal livers and 44 hepatocellular carcinomas. One abundant class of transcripts involves a novel exonic sequence and leads to two alternative (alt.) variants with novel in-frame C-termini of 10 or 65 amino acids. Their hepatic expression was highly variable among individuals, correlated with canonical transcript levels, and was 3.5 fold higher in tumors. Evidence for their translation in liver tissues was acquired by mass spectrometry. In cell models, they co-localized with the enzyme and influenced the conjugation of amitriptyline and levomedetomidine by repressing or activating the enzyme (40-70%; P<0.01), in a cell context-specific manner. A high turnover rate for the alt. proteins, regulated by the proteasome, was observed in contrast to the more stable UGT2B10 enzyme. Moreover, a drug-induced remodelling of UGT2B10 splicing was demonstrated in the HepaRG hepatic cell model, which favored alt. variants expression over the canonical transcript. Our findings support a significant contribution of AS in the regulation of UGT2B10 expression in the liver with an impact on enzyme activity.

The detoxification enzyme UDP-glucuronosyltransferase UGT2B10 is specialized in the N-linked glucuronidation of many drugs and xenobiotics. Preferred substrates possess tertiary aliphatic amines and heterocyclic amines, such as tobacco carcinogens and several antidepressants and antipsychotics. We hypothesized that alternative splicing (AS) constitutes a means to regulate steady-state levels of UGT2B10 and enzyme activity. We established the transcriptome of UGT2B10 in normal and tumoral tissues of multiple individuals. The highest expression was in the liver, where 10 AS transcripts represented 50% of the UGT2B10 transcriptome in 50 normal livers and 44 hepatocellular carcinomas. One abundant class of transcripts involves a novel exonic sequence and leads to two alternative (alt.) variants with novel in-frame C termini of 10 or 65 amino acids. Their hepatic expression was highly variable among individuals, correlated with canonical transcript levels, and was 3.5-fold higher in tumors. Evidence for their translation in liver tissues was acquired by mass spectrometry. In cell models, they colocalized with the enzyme and influenced the conjugation of amitriptyline and levomedetomidine by repressing or activating the enzyme (40%–70%; P < 0.01) in a cell context–specific manner. A high turnover rate for the alt. proteins, regulated by the proteasome, was observed in contrast to the more stable UGT2B10 enzyme. Moreover, a drug-induced remodeling of UGT2B10 splicing was demonstrated in the HepaRG hepatic cell model, which favored alt. variants expression over the canonical transcript. Our findings support a significant contribution of AS in the regulation of UGT2B10 expression in the liver with an impact on enzyme activity.

The conjugative metabolism mediated by UDP-glucuronosyltransferase enzymes (UGTs) significantly influences the bioavailability and biological responses of endogenous molecule substrates and xenobiotics including drugs. UGTs participate in the regulation of cellular homeostasis by limiting stress induced by toxic molecules, and by controlling hormonal signaling networks. Glucuronidation is highly regulated at genomic, transcriptional, post-transcriptional and post-translational levels. However, the UGT protein interaction network, which is likely to influence glucuronidation, has received little attention. We investigated the endogenous protein interactome of human UGT1A enzymes in main drug metabolizing non-malignant tissues, where UGT expression is most prevalent, using an unbiased proteomics approach. Mass spectrometry analysis of affinity-purified UGT1A enzymes and associated protein complexes in liver, kidney and intestine tissues revealed an intricate interactome linking UGT1A enzymes to multiple metabolic pathways. Several proteins of pharmacological importance such as transferases (including UGT2 enzymes), transporters and dehydrogenases were identified, upholding a potential coordinated cellular response to small lipophilic molecules and drugs. Furthermore, a significant cluster of functionally related enzymes involved in fatty acid ß-oxidation, as well as in the glycolysis and glycogenolysis pathways were enriched in UGT1A enzymes complexes. Several partnerships were confirmed by co-immunoprecipitations and co-localization by confocal microscopy. An enhanced accumulation of lipid droplets in a kidney cell model overexpressing the UGT1A9 enzyme supported the presence of a functional interplay. Our work provides unprecedented evidence for a functional interaction between glucuronidation and bioenergetic metabolism.

Alternative splicing at the human glucuronosyltransferase 1 gene locus (UGT1) produces alternate isoforms UGT1A_i2s that control glucuronidation activity through protein-protein interactions. Here, we hypothesized that UGT1A_i2s function into a complex protein network connecting other metabolic pathways with influence on cancer cell metabolism. This is based on a pathway enrichment analysis of proteomic data that identified several high-confidence candidate interaction proteins of UGT1A_i2 proteins in human tissues, namely the rate-limiting enzyme of glycolysis pyruvate kinase (PKM), which plays a critical role in cancer cell metabolism and tumor growth. The partnership of UGT1A_i2 and PKM2 was confirmed by co-immunoprecipitation in the HT115 colon cancer cells and was supported by a partial co-localization of these two proteins. In support of a functional role for this partnership, depletion of UGT1A_i2 proteins in HT115 cells enforced the Warburg effect with higher glycolytic rate at the expense of mitochondrial respiration, and led to lactate accumulation. Untargeted metabolomics further revealed a significantly altered cellular content of 58 metabolites including many intermediates derived from the glycolysis and TCA cycle pathways. These metabolic changes were associated with a greater migration potential. The potential relevance of our observations is supported by the down-regulation of UGT1A_i2s mRNA in colon tumors compared to normal tissues. Alternate UGT1A variants may thus be part of the expanding compendium of metabolic pathways involved in cancer biology directly contributing to the oncogenic phenotype of colon cancer cells. Findings uncover new aspects of UGT functions diverging from their transferase activity.

Alternative splicing as a mean to control gene expression and diversify function is suspected to considerably influence drug response and clearance. We report the quantitative expression profiles of the human UGT genes including alternatively spliced variants not previously annotated established by deep RNA-sequencing in tissues of pharmacological importance. We reveal a comprehensive quantification of the alternative UGT transcriptome that differ across tissues and among individuals. Alternative transcripts that comprise novel in-frame sequences associated or not with truncations of the 5’ and/or 3’ termini, significantly contribute to the total expression levels of each UGT1 and UGT2 gene averaging 21% in normal tissues, with expression of UGT2 variants surpassing those of UGT1. Quantitative data expose preferential tissue expression patterns and remodelling in favour of alternative variants upon tumorigenesis. These complex alternative splicing programs have the strong potential to contribute to interindividual variability in drug metabolism in addition to diversify the UGT proteome.

Alternative splicing at the human glucuronosyltransferase 1 gene locus (UGT1) produces alternate isoforms UGT1A_i2s that control glucuronidation activity through protein-protein interactions. Here, we hypothesized that UGT1A_i2s function into a complex protein network connecting other metabolic pathways with influence on cancer cell metabolism. This is based on a pathway enrichment analysis of proteomic data that identified several high-confidence candidate interaction proteins of UGT1A_i2 proteins in human tissues, namely the rate-limiting enzyme of glycolysis pyruvate kinase (PKM), which plays a critical role in cancer cell metabolism and tumor growth. The partnership of UGT1A_i2 and PKM2 was confirmed by co-immunoprecipitation in the HT115 colon cancer cells and was supported by a partial co-localization of these two proteins. In support of a functional role for this partnership, depletion of UGT1A_i2 proteins in HT115 cells enforced the Warburg effect with higher glycolytic rate at the expense of mitochondrial respiration, and led to lactate accumulation. Untargeted metabolomics further revealed a significantly altered cellular content of 58 metabolites including many intermediates derived from the glycolysis and TCA cycle pathways. These metabolic changes were associated with a greater migration potential. The potential relevance of our observations is supported by the down-regulation of UGT1A_i2s mRNA in colon tumors compared to normal tissues. Alternate UGT1A variants may thus be part of the expanding compendium of metabolic pathways involved in cancer biology directly contributing to the oncogenic phenotype of colon cancer cells. Findings uncover new aspects of UGT functions diverging from their transferase activity.

Alternative splicing as a mean to control gene expression and diversify function is suspected to considerably influence drug response and clearance. We report the quantitative expression profiles of the human UGT genes including alternatively spliced variants not previously annotated established by deep RNA-sequencing in tissues of pharmacological importance. We reveal a comprehensive quantification of the alternative UGT transcriptome that differ across tissues and among individuals. Alternative transcripts that comprise novel in-frame sequences associated or not with truncations of the 5′- and/or 3′- termini, significantly contribute to the total expression levels of each UGT1 and UGT2 gene averaging 21% in normal tissues, with expression of UGT2 variants surpassing those of UGT1. Quantitative data expose preferential tissue expression patterns and remodeling in favor of alternative variants upon tumorigenesis. These complex alternative splicing programs have the strong potential to contribute to interindividual variability in drug metabolism in addition to diversify the UGT proteome.

Glucuronidation, mediated by UDP-glucuronosyltransferase enzymes (UGTs), is a major phase II biotransformation pathway and, complementary to phase I metabolism and membrane transport, one of the most important cellular defense mechanism responsible for the inactivation of therapeutic drugs, other xenobiotics and numerous endogenous molecules. Individual variability in UGT enzymatic pathways is significant and may have profound pharmacological and toxicological implications. Several genetic and genomic processes are underlying this variability and are discussed in the context of drug metabolism and diseases such as cancer.

A comprehensive view of the human UDP-glucuronosyltransferase (UGT) transcriptome is a prerequisite to the establishment of an individual's UGT metabolic glucuronidation signature. Here, we uncover the transcriptome landscape of the 10 human UGT gene loci in normal and tumoral metabolic tissues by targeted RNA next-generation sequencing. Alignment on the human hg19 reference genome identifies 234 novel exon-exon junctions. We recover all previously known UGT1 and UGT2 enzyme-coding transcripts and identify over 130 structurally and functionally diverse novel UGT variants. We further expose a revised genomic structure of UGT loci and provide a comprehensive repertoire of transcripts for each UGT gene. Data also uncover a remodelling of the UGT transcriptome occurring in a tissue- and tumor-specific manner. The complex alternative splicing program regulating UGT expression and protein functions is likely critical in determining detoxification capacity of an organ and stress-related responses, with significant impact on drug responses and diseases.

A comprehensive view of the human UDP-glucuronosyltransferase (UGT) transcriptome is a prerequisite to the establishment of an individual’s UGT metabolic glucuronidation signature. Here, we uncover the transcriptome landscape of the ten human UGT loci genes in normal and tumoral metabolic tissues by targeted RNA next generation sequencing. Alignment on the human hg19 reference genome identifies 234 novel exon-exon junctions. We recover all previously known UGT1 and UGT2 enzyme-coding transcripts and identify over 130 structurally and functionally diverse novel UGT variants. We further expose a revised genomic structure of UGT loci and provide a comprehensive repertoire of transcripts for each UGT gene. Data also uncover a remodelling of the UGT transcriptome occurring in a tissue- and tumor-specific manner. The complex alternative splicing program regulating UGT expression and protein functions is likely critical in determining detoxification capacity of an organ and stress-related responses, with significant impact on drug responses and diseases. Keywords: Alternative splicing, transcriptome, glucuronidation, RNA sequencing, drug metabolism, glucuronosyltransferase (UGT)

Glucuronidation, mediated by UDP-glucuronosyltransferase enzymes (UGTs), is a major phase II biotransformation pathway and, complementary to phase I metabolism and membrane transport, one of the most important cellular defense mechanism responsible for the inactivation of therapeutic drugs, other xenobiotics and numerous endogenous molecules. Individual variability in UGT enzymatic pathways is significant and may have profound pharmacological and toxicological implications. Several genetic and genomic processes are underlying this variability and are discussed in the context of drug metabolism and diseases such as cancer.