Protein kinase Cα and Src kinase support human prostate-distributed dihydrotestosterone-metabolizing UDP-glucuronosyltransferase 2B15 activity

Exploring the therapeutic mechanism of curcumin in prostate cancer using network pharmacology and molecular docking

Objective

Curcumin, a phenolic compound extracted from turmeric rhizomes, exhibits antitumour effects in preclinical models of tumours. However, its mechanism of action in prostate cancer remains unclear. Exploring the molecular mechanisms of curcumin in prostate cancer based on network pharmacology and molecular docking provides a new theoretical basis for prostate cancer treatment.

Method

Using tools such as PharmMapper, SuperPred, TargetNet, and SwissTargetPrediction, we obtained information on curcumin-related targets. We comprehensively collected prostate cancer-related targets from several databases, including GeneCards, CTD, DisGeNET, OMIM, and PharmGKB. Cross-cutting drug-disease targets were then derived by screening using the Venny 2.1.0 tool. Subsequently, we used the DAVID platform to perform in-depth GO and KEGG enrichment analyses of the drug-disease-shared targets. To construct a PPI network map of the cross-targets and screen the 10 core targets, we combined the STRING database and Cytoscape 3.7.2. Molecular docking experiments were performed using AutoDockTools 1.5.7 software. Finally, we used several databases such as GEPIA, HPA, cBioPortal, and TIMER to further analyse the screened core targets in detail.

Result

We identified 307 key targets of curcumin in cancer treatment. After GO functional enrichment analysis, we obtained 1119 relevant entries, including 782 biological progression (BP) entries, 112 cellular component (CC) entries, and 225 molecular function (MF) entries. In addition, KEGG pathway enrichment analysis revealed 126 signalling pathways, which were mainly involved in the cancer pathway, such as lipid and atherosclerosis pathway, PI3K-Akt signal pathway, MAPK signal pathway, Ras signal pathways, and chemical carcinogenesis-reactive oxygen species. By applying Cytoscape 3.7.2 software, we identified SRC, PIK3R1, STAT3, AKT1, HSP90AA1, ESR1, EGFR, HSP90AB1, MAPK8, and MAPK1 as core targets. Molecular docking experiments showed that the binding energies of curcumin to these core targets were all below -1.85 kJ mol-1, which fully demonstrated that curcumin could spontaneously bind to these core targets. Finally, these results were validated at multiple levels, including mRNA expression, protein expression, and immune infiltration.

Conclusion

Through in-depth network pharmacology and molecular docking studies, we have found that curcumin may have anticancer potential by upregulating the expression of PIK3R1 and STAT3, and downregulating the binding ability of molecules such as SRC, AKT1, HSP90AA1, ESR1, EGFR, HSP90AB1, MAPK8, and MAPK1. In addition, curcumin may interfere with the cyclic process of prostate cancer cells by inhibiting key signalling pathways such as the PI3K-Akt signalling pathway, MAPK signalling pathway, and Ras, thereby inhibiting their growth. This study not only reveals the potential molecular mechanism of curcumin in the treatment of prostate cancer but also provides an important theoretical basis for subsequent research.

The Uridine diphosphate (UDP)-glycosyltransferases (UGTs) superfamily: the role in tumor cell metabolism

UDP-glycosyltransferases (UGTs), important enzymes in biotransformation, control the levels and distribution of numerous endogenous signaling molecules and the metabolism of a wide range of endogenous and exogenous chemicals. The UGT superfamily in mammals consists of the UGT1, UGT2, UGT3, and UGT8 families. UGTs are rate-limiting enzymes in the glucuronate pathway, and in tumors, they are either overexpressed or underexpressed. Alterations in their metabolism can affect gluconeogenesis and lipid metabolism pathways, leading to alterations in tumor cell metabolism, which affect cancer development and prognosis. Glucuronidation is the most common mammalian conjugation pathway. Most of its reactions are mainly catalyzed by UGT1A, UGT2A and UGT2B. The body excretes UGT-bound small lipophilic molecules through the bile, urine, or feces. UGTs conjugate a variety of tiny lipophilic molecules to sugars, such as galactose, xylose, acetylglucosamine, glucuronic acid, and glucose, thereby inactivating and making water-soluble substrates, such as carcinogens, medicines, steroids, lipids, fatty acids, and bile acids. This review summarizes the roles of members of the four UGT enzyme families in tumor function, metabolism, and multiple regulatory mechanisms, and its Inhibitors and inducers. The function of UGTs in lipid metabolism, drug metabolism, and hormone metabolism in tumor cells are among the most important topics covered.

The UGTome: The expanding diversity of UDP glycosyltransferases and its impact on small molecule metabolism

The UDP glycosyltransferase (UGT) superfamily of enzymes is responsible for the metabolism and clearance of thousands of lipophilic chemicals including drugs, toxins and endogenous signaling molecules. They provide a protective interface between the organism and its chemical-rich environment, as well as controlling critical signaling pathways to maintain healthy tissue function. UGTs are associated with drug responses and interactions, as well as a wide range of diseases including cancer. The human genome contains 22 UGT genes; however as befitting their exceptionally diverse substrate ranges and biological activities, the output of these UGT genes is functionally diversified by multiple processes including alternative splicing, post-translational modification, homo- and hetero-oligomerization, and interactions with other proteins. All UGT genes are subject to extensive alternative splicing generating variant/truncated UGT proteins with altered functions including the capacity to dominantly modulate/inhibit cognate full-length forms. Heterotypic oligomerization of different UGTs can alter kinetic properties relative to monotypic complexes, and potentially produce novel substrate specificities. Moreover, the recently profiled interactions of UGTs with non-UGT proteins may facilitate coordination between different metabolic processes, as well as providing opportunities for UGTs to engage in novel 'moonlighting' functions. Herein we provide a detailed and comprehensive review of all known modes of UGT functional diversification and propose a UGTome model to describe the resulting expansion of metabolic capacity and its potential to modulate drug/xenobiotic responses and cell behaviours in normal and disease contexts.

The UDP-Glycosyltransferase (UGT) Superfamily: New Members, New Functions, and Novel Paradigms

UDP-glycosyltransferases (UGTs) catalyze the covalent addition of sugars to a broad range of lipophilic molecules. This biotransformation plays a critical role in elimination of a broad range of exogenous chemicals and by-products of endogenous metabolism, and also controls the levels and distribution of many endogenous signaling molecules. In mammals, the superfamily comprises four families: UGT1, UGT2, UGT3, and UGT8. UGT1 and UGT2 enzymes have important roles in pharmacology and toxicology including contributing to interindividual differences in drug disposition as well as to cancer risk. These UGTs are highly expressed in organs of detoxification (e.g., liver, kidney, intestine) and can be induced by pathways that sense demand for detoxification and for modulation of endobiotic signaling molecules. The functions of the UGT3 and UGT8 family enzymes have only been characterized relatively recently; these enzymes show different UDP-sugar preferences to that of UGT1 and UGT2 enzymes, and to date, their contributions to drug metabolism appear to be relatively minor. This review summarizes and provides critical analysis of the current state of research into all four families of UGT enzymes. Key areas discussed include the roles of UGTs in drug metabolism, cancer risk, and regulation of signaling, as well as the transcriptional and posttranscriptional control of UGT expression and function. The latter part of this review provides an in-depth analysis of the known and predicted functions of UGT3 and UGT8 enzymes, focused on their likely roles in modulation of levels of endogenous signaling pathways.

A Rare UGT2B7 Variant Creates a Novel N-Glycosylation Site at Codon 121 with Impaired Enzyme Activity

The UDP glucuronosyltransferase (UGT) superfamily comprises glycoproteins that reside in the endoplasmic reticulum membranes and that undergo post-translational modifications (PTMs). UGT2B7 is of particular interest because of its action on a wide variety of drugs. Most studies currently survey common variants and examine only a small fraction of the genetic diversity; however, rare variants (frequency <1%) might have a significant effect because they are predicted to greatly outnumber common variants in the human genome. We discovered a rare single nucleotide UGT2B7 variant of potential pharmacogenetic relevance that encodes a nonconservative amino acid substitution at codon 121. This low-frequency variation, found in two individuals of a population of 305 healthy volunteers, leads to the translation of an asparagine instead of an aspartic acid (UGT2B7 p.D121N). This amino acid change was predicted to create a putative N-glycosylation motif NX(S/T) subsequently validated upon endoglycosidase H treatment of microsomal fractions and inhibition of N-glycosylation of endogenously produced UGT2B7 with tunicamycin in human embryonic kidney (HEK293) cells. The presence of an additional N-linked glycan on the UGT2B7 enzyme, likely affecting proper protein folding, resulted in a significant decrease of 49% and 40% in the formation of zidovudine and mycophenolic acid glucuronides, respectively. A systematic survey of the Short Genetic Variations database uncovered 32 rare, naturally occurring missense variations predicted to create or disrupt N-glycosylation sequence motifs in the other UGT2B enzymes. Collectively, these variants have the potential to increase the proportion of variance explained in the UGT pathway resulting from changes in PTMs, such as N-linked glycosylation with consequences on drug metabolism.

Regulation of uridine diphosphate-glucuronosyltransferase 1A3 activity by protein phosphorylation

Protein phosphorylation is a vital post-translational modification. This study investigated the effect of phosphorylation on human uridine diphosphate (UDP)-glucuronosyltransferase 1A3 (UGT1A3) activity. Curcumin and calphostin C suppressed the activity and phosphorylation of recombinant UGT1A3 expressed in Sf9 cells. These results indicate that UGT1A3 undergoes phosphorylation, which is required for its catalytic activity. Calphostin C is a highly specific protein kinase C (PKC) inhibitor, so three predicted PKC phosphorylation sites in UGT1A3 were examined. Site-directed mutation analysis at residues 28, 43 and 436 (from serine to glycine) was conducted. Compared with the wild-type, the S43G-mutant showed significantly decreased UGT1A3 catalytic activity. Furthermore, the UGT1A3 activity of wild-type and S43G-mutant was down-regulated by calphostin C, whereas the calphostin C inhibitory effect was much weaker on the S43G-mutant than the wild-type. In conclusion, phosphorylation plays an important role in UGT1A3 activity, and the serine at site 43 in UGT1A3 is most likely a phosphorylation site.

Posttranscriptional regulation of uridine diphosphate glucuronosyltransferases

INTRODUCTION

The uridine diphosphate (UDP)-glucuronosyltransferase (UGT) superfamily of enzymes (EC 2.4.1.17) conjugates glucuronic acid to an aglycone substrate to make them more polar and readily excreted. In general, this reaction terminates the activities of chemicals, drugs and toxins, although occasionally a more active or toxic species is produced.

AREAS COVERED

In addition to their well-known transcriptional responsiveness, UGTs are also regulated by posttranscriptional mechanisms. Here, the authors review these mechanisms, including latency, modulation of co-substrate accessibility and binding, dimerization and oligomerization, protein-protein interactions, allosteric inhibition and activation, posttranslational structural and functional modifications and developmental switching for UGTs.

EXPERT OPINION

Posttranscriptional regulation of UGTs has traditionally received less attention than nuclear regulation, in part because mechanisms involving ribosomes and endoplasmic reticula are challenging to investigate. Most promising of the posttranscriptional mechanisms reviewed are likely to be effects on co-substrate (UDP-glucuronic acid) transport and availability and structure-function changes to UGT proteins through, for example, glycosylation and phosphorylation. Although classical biochemistry continues to illuminate many aspects of UGT function, advances in proteomics and structural biology are beginning to assist in the determination of posttranscriptional regulation mechanisms for UGTs.

Transcriptional regulation of human UDP-glucuronosyltransferase genes

Glucuronidation is an important metabolic pathway for many small endogenous and exogenous lipophilic compounds, including bilirubin, steroid hormones, bile acids, carcinogens and therapeutic drugs. Glucuronidation is primarily catalyzed by the UDP-glucuronosyltransferase (UGT) 1A and two subfamilies, including nine functional UGT1A enzymes (1A1, 1A3-1A10) and 10 functional UGT2 enzymes (2A1, 2A2, 2A3, 2B4, 2B7, 2B10, 2B11, 2B15, 2B17 and 2B28). Most UGTs are expressed in the liver and this expression relates to the major role of hepatic glucuronidation in systemic clearance of toxic lipophilic compounds. Hepatic glucuronidation activity protects the body from chemical insults and governs the therapeutic efficacy of drugs that are inactivated by UGTs. UGT mRNAs have also been detected in over 20 extrahepatic tissues with a unique complement of UGT mRNAs seen in almost every tissue. This extrahepatic glucuronidation activity helps to maintain homeostasis and hence regulates biological activity of endogenous molecules that are primarily inactivated by UGTs. Deciphering the molecular mechanisms underlying tissue-specific UGT expression has been the subject of a large number of studies over the last two decades. These studies have shown that the constitutive and inducible expression of UGTs is primarily regulated by tissue-specific and ligand-activated transcription factors (TFs) via their binding to cis-regulatory elements (CREs) in UGT promoters and enhancers. This review first briefly summarizes published UGT gene transcriptional studies and the experimental models and tools utilized in these studies, and then describes in detail the TFs and their respective CREs that have been identified in the promoters and/or enhancers of individual UGT genes.