A global functional analysis of missense mutations reveals two major hotspots in the PALB2 tumor suppressor.

While biallelic mutations in the PALB2 tumor suppressor cause Fanconi anemia subtype FA-N, monoallelic mutations predispose to breast and familial pancreatic cancer. Although hundreds of missense variants in PALB2 have been identified in patients to date, only a few have clear functional and clinical relevance. Herein, we investigate the effects of 44 PALB2 variants of uncertain significance found in breast cancer patients and provide detailed analysis by systematic functional assays. Our comprehensive functional analysis reveals two hotspots for potentially deleterious variations within PALB2, one at each terminus. PALB2 N-terminus variants p.P8L [c.23C>T], p.Y28C [c.83A>G], and p.R37H [c.110G>A] compromised PALB2-mediated homologous recombination. At the C-terminus, PALB2 variants p.L947F [c.2841G>T], p.L947S [c.2840T>C], and most strikingly p.T1030I [c.3089C>T] and p.W1140G [c.3418T>C], stood out with pronounced PARP inhibitor sensitivity and cytoplasmic accumulation in addition to marked defects in recruitment to DNA damage sites, interaction with BRCA2 and homologous recombination. Altogether, our findings show that a combination of functional assays is necessary to assess the impact of germline missense variants on PALB2 function, in order to guide proper classification of their deleteriousness.

The Tumor Suppressor PALB2: Inside Out.

Partner and Localizer of BRCA2 (PALB2) has emerged as an important and versatile player in genome integrity maintenance. Biallelic mutations in PALB2 cause Fanconi anemia (FA) subtype FA-N, whereas monoallelic mutations predispose to breast, and pancreatic familial cancers. Herein, we review recent developments in our understanding of the mechanisms of regulation of the tumor suppressor PALB2 and its functional domains. Regulation of PALB2 functions in DNA damage response and repair occurs on multiple levels, including homodimerization, phosphorylation, and ubiquitylation. With a molecular emphasis, we present PALB2-associated cancer mutations and their detailed analysis by functional assays.

Epigenetic regulation of steroid inactivating UDP-glucuronosyltransferases by microRNAs in prostate cancer.

Androgens play a central role in prostate cancer progression. Systemic and local androgen bioavailability is controlled by UDP-glucuronosyltransferases conjugating enzymes (UGT), namely UGT2B15, UGT2B17 and UGT2B28. Reporter vector assays in HEK293 cells initially validated in silico-predicted regulatory potential of candidate miRNAs to target UGT transcripts, including miR-376c, miR-409 and miR-494 for UGT2B17, miR-331-5p and miR-376c for UGT2B15 while none were efficient for UGT2B28. miR-376c was shown as the most effective to downregulate UGT2B15 and UGT2B17 through interactions with a site conserved in both UGTs. Ectopic miR-376c expression in prostate cancer cells significantly reduced UGT2B15 and UGT2B17 expression (>32%; P<0.005) with a consequent decrease in dihydrotestosterone glucuronidation (-37%; P<0.001). Consistent with reduced androgen inactivation, ectopic expression of miR-376c changed expression of androgen responsive genes and enhanced cell proliferation with no effect on androgen receptor levels. Sustaining a role of miR-376c in the regulation of androgen-inactivating UGTs, its expression was significantly downregulated in prostatic tumors and further reduced in metastases (P<0.0001), whereas the opposite was observed for UGT2B15/17 (P=0.031). In high-grade tumors (Gleason ≥8), UGT2B15/17 and miR-376c were inversely correlated (r=-0.557; P=0.048) with also a significant relationship in metastases (r=-0.747; P=0.003). In line with a modification in androgen bioavailability, PSA mRNA levels were also negatively correlated to those of UGT2B15/17 (r=-0.573; P=0.01) but positively linked to levels of miR-376c (r=0.577; P=0.039). This study reveals that the androgen-inactivating UGT2B15 and UGT2B17 genes are direct targets of miR-376c and thus may influence steroid metabolism during prostate cancer progression.

Multiplexed Targeted Quantitative Proteomics Predicts Hepatic Glucuronidation Potential.

Phase II metabolism is prominently governed by UDP-glucuronosyltransferases (UGTs) in humans. These enzymes regulate the bioactivity of many drugs and endogenous small molecules in many organs, including the liver, a major site of regulation by the glucuronidation pathway. This study determined the expression of hepatic UGTs by targeted proteomics in 48 liver samples and by measuring the glucuronidation activity using probe substrates. It demonstrates the sensitivity and accuracy of nano-ultra-performance liquid chromatography with tandem mass spectrometry to establish the complex expression profiles of 14 hepatic UGTs in a single analysis. UGT2B7 is the most abundant UGT in our collection of livers, expressed at 69 pmol/mg microsomal proteins, whereas UGT1A1, UGT1A4, UGT2B4, and UGT2B15 are similarly abundant, averaging 30-34 pmol/mg proteins. The average relative abundance of these five UGTs represents 81% of the measured hepatic UGTs. Our data further highlight the strong relationships in the expression of several UGTs. Most notably, UGT1A4 correlates with most measured UGTs, and the expression levels of UGT2B4/UGT2B7 displayed the strongest correlation. However, significant interindividual variability is observed for all UGTs, both at the level of enzyme concentrations and activity (coefficient of variation: 45%-184%). The reliability of targeted proteomics quantification is supported by the high correlation between UGT concentration and activity. Collectively, these findings expand our understanding of hepatic UGT profiles by establishing absolute hepatic concentrations of 14 UGTs and further suggest coregulated expression between most abundant hepatic UGTs. Data support the value of multiplexed targeted quantitative proteomics to accurately assess specific UGT concentrations in liver samples and hepatic glucuronidation potential.

Quantitative profiling of human renal UDP-glucuronosyltransferases and glucuronidation activity: a comparison of normal and tumoral kidney tissues.

Renal metabolism by UDP-glucuronosyltransferase (UGT) enzymes is central to the clearance of many drugs. However, significant discrepancies about the relative abundance and activity of individual UGT enzymes in the normal kidney prevail among reports, whereas glucuronidation in tumoral kidney has not been examined. In this study, we performed an extensive profiling of glucuronidation metabolism in normal (n = 12) and tumor (n = 14) kidneys using targeted mass spectrometry quantification of human UGTs. We then correlated UGT protein concentrations with mRNA levels assessed by quantitative polymerase chain reaction and with conjugation activity for the major renal UGTs. Beyond the wide interindividual variability in expression levels observed among kidney samples, UGT1A9, UGT2B7, and UGT1A6 are the most abundant renal UGTs in both normal and tumoral tissues based on protein quantification. In normal kidney tissues, only UGT1A9 protein levels correlated with mRNA levels, whereas UGT1A6, UGT1A9, and UGT2B7 quantification correlated significantly with their mRNA levels in tumor kidneys. Data support that posttranscriptional regulation of UGT2B7 and UGT1A6 expression is modulating glucuronidation in the kidney. Importantly, our study reveals a significant decreased glucuronidation capacity of neoplastic kidneys versus normal kidneys that is paralleled by drastically reduced UGT1A9 and UGT2B7 mRNA and protein expression. UGT2B7 activity is the most repressed in tumors relative to normal tissues, with a 96-fold decrease in zidovudine metabolism, whereas propofol and sorafenib glucuronidation is decreased by 7.6- and 5.2-fold, respectively. Findings demonstrate that renal drug metabolism is predominantly mediated by UGT1A9 and UGT2B7 and is greatly reduced in kidney tumors.

Modulation of the UGT2B7 enzyme activity by C-terminally truncated proteins derived from alternative splicing.

The enzyme UGT2B7 is one of the most active UDP-glucuronosyltransferases (UGTs) involved in drug metabolism and in maintaining homeostasis of endogenous compounds. We recently reported the existence of 22 UGT2B7 mRNAs, two with a classic 5' region but alternative 3' ends namely UGT2B7_v5 (containing a novel terminal exon 6b) and _v7 (exon 5 excluded) that encode enzymatically inactive isoforms 2 and 4 (i2 and i4), respectively. The v1 mRNA encoding the UGT2B7 enzyme (renamed isoform 1 or i1) is coexpressed with the splice variants v5 and v7 in human liver, kidney, and small intestine and the hepatic cell lines HepG2 and C3A. The presence of alternate v5 and v7 transcripts in isolated polysomes from these hepatic cells further supports endogenous protein translation. Cellular fractionation of clonal HEK293 cell lines overexpressing UGT2B7 isoforms demonstrates that i1, i2, and i4 proteins colocalize in the microsomal/Golgi fraction, whereas i2 and i4 can also be found in the cytosol; a finding sustained by immunofluorescence experiments using tagged proteins. By modifying splice variant abundance in overexpression in HEK293 and HepG2 cells as well as RNA interference experiments in HepG2 and C3A cells, we observe drug glucuronidation phenotypes compatible with variant-mediated repression of UGT2B7 activity without consequent alteration of the apparent enzyme affinity (K(m)). Finally, coimmunoprecipitation experiments support a direct protein-protein interaction of i2 and i4 proteins with the functional UGT2B7 enzyme as a potential causative mechanism. These findings point toward a novel autoregulatory mechanism of the UGT2B7 glucuronidation pathway by naturally occurring alternative i2 and i4 proteins.

The emergence of new therapeutic targets in pulmonary arterial hypertension: from now to the near future.

Pulmonary arterial hypertension (PAH) is a vascular remodeling disease that pathologically increases pulmonary vascular resistance. Ultimately, this leads to right ventricular failure and premature death. Current therapeutic strategies are mainly designed to induce relaxation of the pulmonary arteries, but are not directly aimed to improve vascular remodeling that characterize PAH. Although these treatments modestly improve patient symptoms, pulmonary hemodynamics and survival, none of them are curative and approximately 15% of patients die within 1 year of medical follow-up despite treatment. Within the last 5 years, tremendous advances in our understanding of the PAH pathophysiology have arisen. These advances have a high potential for the development of better patient care by providing novel therapeutic targets. The goal of this report is to review the current PAH treatments, as well as novel therapies that will pave the future in this devastating disease.