Purification and characterization of a novel form of 20 alpha-hydroxysteroid dehydrogenase from Clostridium scindens

Clostridium scindens metabolites trigger prostate cancer progression through androgen receptor signaling

Prostate cancer (PCa) is one of the most common malignancies in men; recently, PCa-related mortality has increased worldwide. Although androgen deprivation therapy (ADT) is the standard treatment for PCa, patients often develop aggressive castration-resistant PCa (CRPC), indicating the presence of an alternative source of androgen. Clostridium scindens is a member of the gut microbiota and can convert cortisol to 11β-hydroxyandrostenedione (11β-OHA), which is a potent androgen precursor. However, the effect of C. scindens on PCa progression has not been determined. In this study, androgen-dependent PCa cells (LNCaP) were employed to investigate whether C. scindens-derived metabolites activate androgen receptor (AR), which is a pivotal step in the development of PCa. Results showed that cortisol metabolites derived from C. scindens-conditioned medium promoted proliferation and enhanced migration of PCa cells. Furthermore, cells treated with these metabolites presented activated AR and stimulated AR-regulated genes. These findings reveal that C. scindens has the potential to promote PCa progression via the activation of AR signaling. Further studies on the gut-prostate axis may help unravel an alternative source of androgen that triggers CRPC exacerbation.

Gut feelings about bacterial steroid-17,20-desmolase

Advances in technology are only beginning to reveal the complex interactions between hosts and their resident microbiota that have co-evolved over centuries. In this review, we present compelling evidence that implicates the host-associated microbiome in the generation of 11β-hydroxyandrostenedione, leading to the formation of potent 11-oxy-androgens. Microbial steroid-17,20-desmolase cleaves the side-chain of glucocorticoids (GC), including cortisol (and its derivatives of cortisone, 5α-dihydrocortisol, and also (allo)- 3α, 5α-tetrahydrocortisol, but not 3α-5β-tetrahydrocortisol) and drugs (prednisone and dexamethasone). In addition to side-chain cleavage, we discuss the gut microbiome's robust potential to transform a myriad of steroids, mirroring much of the host's metabolism. We also explore the overlooked role of intestinal steroidogenesis and efflux pumps as a potential route for GC transport into the gut. Lastly, we propose several health implications from microbial steroid-17,20-desmolase function, including aberrant mineralocorticoid, GC, and androgen receptor signaling in colonocytes, immune cells, and prostate cells, which may exacerbate disease states.

Microbial Hydroxysteroid Dehydrogenases: From Alpha to Omega

Bile acids (BAs) and glucocorticoids are steroid hormones derived from cholesterol that are important signaling molecules in humans and other vertebrates. Hydroxysteroid dehydrogenases (HSDHs) are encoded both by the host and by their resident gut microbiota, and they reversibly convert steroid hydroxyl groups to keto groups. Pairs of HSDHs can reversibly epimerize steroids from α-hydroxy conformations to β-hydroxy, or β-hydroxy to ω-hydroxy in the case of ω-muricholic acid. These reactions often result in products with drastically different physicochemical properties than their precursors, which can result in steroids being activators or inhibitors of host receptors, can affect solubility in fecal water, and can modulate toxicity. Microbial HSDHs modulate sterols associated with diseases such as colorectal cancer, liver cancer, prostate cancer, and polycystic ovary syndrome. Although the role of microbial HSDHs is not yet fully elucidated, they may have therapeutic potential as steroid pool modulators or druggable targets in the future. In this review, we explore metabolism of BAs and glucocorticoids with a focus on biotransformation by microbial HSDHs.

Conceptualizing the Vertebrate Sterolbiome

Vertebrates synthesize a diverse set of steroids and bile acids that undergo bacterial biotransformations. The endocrine literature has principally focused on the biochemistry and molecular biology of host synthesis and tissue-specific metabolism of steroids. Host-associated microbiota possess a coevolved set of steroid and bile acid modifying enzymes that match the majority of host peripheral biotransformations in addition to unique capabilities. The set of host-associated microbial genes encoding enzymes involved in steroid transformations is known as the sterolbiome. This review focuses on the current knowledge of the sterolbiome as well as its importance in medicine and agriculture.

Bacterial steroid-17,20-desmolase is a taxonomically rare enzymatic pathway that converts prednisone to 1,4-androstanediene-3,11,17-trione, a metabolite that causes proliferation of prostate cancer cells

The adrenal gland has traditionally been viewed as a source of "weak androgens"; however, emerging evidence indicates 11-oxy-androgens of adrenal origin are metabolized in peripheral tissues to potent androgens. Also emerging is the role of gut bacteria in the conversion of C₂₁ glucocorticoids to 11-oxygenated C₁₉ androgens. Clostridium scindens ATCC 35,704 is a gut microbe capable of converting cortisol into 11-oxy-androgens by cleaving the side-chain. The desA and desB genes encode steroid-17,20-desmolase. Our prior study indicated that the urinary tract bacterium, Propionimicrobium lymphophilum ACS-093-V-SCH5 encodes desAB and converts cortisol to 11β-hydroxyandrostenedione. We wanted to determine how widespread this function occurs in the human microbiome. Phylogenetic and sequence similarity network analyses indicated that the steroid-17,20-desmolase pathway is taxonomically rare and located in gut and urogenital microbiomes. Two microbes from each of these niches, C. scindens and Propionimicrobium lymphophilum, respectively, were screened for activity against endogenous (cortisol, cortisone, and allotetrahydrocortisol) and exogenous (prednisone, prednisolone, dexamethasone, and 9-fluorocortisol) glucocorticoids. LC/MS analysis showed that both microbes were able to side-chain cleave all glucocorticoids, forming 11-oxy-androgens. Pure recombinant DesAB from C. scindens showed the highest activity against prednisone, a commonly prescribed glucocorticoid. In addition, 0.1 nM 1,4-androstadiene-3,11,17-trione, bacterial side-chain cleavage product of prednisone, showed significant proliferation relative to vehicle in androgen-dependent growth LNCaP prostate cancer cells after 24 h (2.3 fold; P <  0.01) and 72 h (1.6 fold; P < 0.01). Taken together, DesAB-expressing microbes may be an overlooked source of androgens in the body, potentially contributing to various disease states, such as prostate cancer.

The desA and desB genes from Clostridium scindens ATCC 35704 encode steroid-17,20-desmolase

Clostridium scindens is a gut microbe capable of removing the side-chain of cortisol, forming 11β-hydro-xyandrostenedione. A cortisol-inducible operon (desABCD) was previously identified in C. scindens ATCC 35704 by RNA-Seq. The desC gene was shown to encode a cortisol 20α-hydroxysteroid dehydrogenase (20α-HSDH). The desD encodes a protein annotated as a member of the major facilitator family, predicted to function as a cortisol transporter. The desA and desB genes are annotated as N-terminal and C-terminal transketolases, respectively. We hypothesized that the DesAB forms a complex and has steroid-17,20-desmolase activity. We cloned the desA and desB genes from C. scindens ATCC 35704 in pETDuet for overexpression in Escherichia coli The purified recombinant DesAB was determined to be a 142 ± 5.4 kDa heterotetramer. We developed an enzyme-linked continuous spectrophotometric assay to quantify steroid-17,20-desmolase. This was achieved by coupling DesAB-dependent formation of 11β-hydroxyandrostenedione with the NADPH-dependent reduction of the steroid 17-keto group by a recombinant 17β-HSDH from the filamentous fungus, Cochliobolus lunatus The pH optimum for the coupled assay was 7.0 and kinetic constants using cortisol as substrate were K_m of 4.96 ± 0.57 µM and k_cat of 0.87 ± 0.076 min^-1 Substrate-specificity studies revealed that rDesAB recognized substrates regardless of 11β-hydroxylation, but had an absolute requirement for 17,21-dihydroxy 20-ketosteroids.

Glucocorticoids and gut bacteria: "The GALF Hypothesis" in the metagenomic era

A new concept is emerging in biomedical sciences: the gut microbiota is a virtual 'organ' with endocrine function. Here, we explore the literature pertaining to the role of gut microbial metabolism of endogenous adrenocorticosteroids as a contributing factor in the etiology of essential hypertension. A body of literature demonstrates that bacterial products of glucocorticoid metabolism are absorbed into the portal circulation, and pass through the kidney before excretion into urine. Apparent mineralocorticoid excess (AME) syndrome patients were found to have congenital mutations resulting in non-functional renal 11β-hydroxysteroid dehydrogenase-2 (11β-HSD2) and severe hypertension often lethal in childhood. 11β-HSD2 acts as a "guardian" enzyme protecting the mineralocorticoid receptor from excess cortisol, preventing sodium and water retention in the normotensive state. Licorice root, whose active ingredient, glycerrhetinic acid (GA), inhibits renal 11β-HSD2, and thereby causes hypertension in some individuals. Bacterially derived glucocorticoid metabolites may cause hypertension in some patients by a similar mechanism. Parallel observations in gut microbiology coupled with screening of endogenous steroids as inhibitors of 11β-HSD2 have implicated particular gut bacteria in essential hypertension through the production of glycerrhetinic acid-like factors (GALFs). A protective role of GALFs produced by gut bacteria in the etiology of colorectal cancer is also explored.

Identification and characterization of a 20β-HSDH from the anaerobic gut bacterium Butyricicoccus desmolans ATCC 43058

Members of the gastrointestinal microbiota are known to convert glucocorticoids to androstanes, which are subsequently converted to potent androgens by other members of the gut microbiota or host tissues. Butyricicoccus desmolans and Clostridium cadaveris have previously been reported for steroid-17,20-desmolase and 20β-hydroxysteroid dehydrogenase (HSDH) activities that are responsible for androstane formation from cortisol; however, the genes encoding these enzymes have yet to be reported. In this work, we identified and located a gene encoding 20β-HSDH in both B. desmolans and C. cadaveris The 20β-HSDH of B. desmolans was heterologously overexpressed and purified from Escherichia coli The enzyme was determined to be a homotetramer with subunit molecular mass of 33.8 ± 3.7 kDa. The r20β-HSDH displayed pH optimum in the reductive direction at pH 9.0 and in the oxidative direction at pH 7.0-7.5 with (20β-dihydro)cortisol and NAD(H) as substrates. Cortisol is the preferred substrate with K_m , 0.80 ± 0.06 μM; V_max , 30.36 ± 1.97 μmol·min^-1; K_cat , 607 ± 39 μmol·μM^-1·min^-1; K_cat /K_m , 760 ± 7.67. Phylogenetic analysis of the 20β-HSDH from B. desmolans suggested that the 20β-HSDH is found in several Bifidobacterium spp, one of which was shown to express 20β-HSDH activity. Notably, we also identified a novel steroid-17,20-desmolase-elaborating bacterium, Propionimicrobium lymphophilum, a normal inhabitant of the urinary tract.

Clostridium scindens: a human gut microbe with a high potential to convert glucocorticoids into androgens

Clostridium scindens American Type Culture Collection 35704 is capable of converting primary bile acids to toxic secondary bile acids, as well as converting glucocorticoids to androgens by side-chain cleavage. The molecular structure of the side-chain cleavage product of cortisol produced by C. scindens was determined to be 11β-hydroxyandrost-4-ene-3,17-dione (11β-OHA) by high-resolution mass spectrometry, ¹H and ¹³C NMR spectroscopy, and X-ray crystallography. Using RNA-Seq technology, we identified a cortisol-inducible (∼1,000-fold) operon (desABCD) encoding at least one enzyme involved in anaerobic side-chain cleavage. The desC gene was cloned, overexpressed, purified, and found to encode a 20α-hydroxysteroid dehydrogenase (HSDH). This operon also encodes a putative “transketolase” (desAB) hypothesized to have steroid-17,20-desmolase/oxidase activity, and a possible corticosteroid transporter (desD). RNA-Seq data suggests that the two-carbon side chain of glucocorticords may feed into the pentose-phosphate pathway and are used as a carbon source. The 20α-HSDH is hypothesized to function as a metabolic “rheostat” controlling rates of side-chain cleavage. Phylogenetic analysis suggests this operon is rare in nature and the desC gene evolved from a gene encoding threonine dehydrogenase. The physiological effect of 11β-OHAD on the host or other gut microbes is currently unknown.

Hydroxysteroid dehydrogenases (HSDs) in bacteria: a bioinformatic perspective

Steroidal compounds including cholesterol, bile acids and steroid hormones play a central role in various physiological processes such as cell signaling, growth, reproduction, and energy homeostasis. Hydroxysteroid dehydrogenases (HSDs), which belong to the superfamily of short-chain dehydrogenases/reductases (SDR) or aldo-keto reductases (AKR), are important enzymes involved in the steroid hormone metabolism. HSDs function as an enzymatic switch that controls the access of receptor-active steroids to nuclear hormone receptors and thereby mediate a fine-tuning of the steroid response. The aim of this study was the identification of classified functional HSDs and the bioinformatic annotation of these proteins in all complete sequenced bacterial genomes followed by a phylogenetic analysis. For the bioinformatic annotation we constructed specific hidden Markov models in an iterative approach to provide a reliable identification for the specific catalytic groups of HSDs. Here, we show a detailed phylogenetic analysis of 3α-, 7α-, 12α-HSDs and two further functional related enzymes (3-ketosteroid-Δ(1)-dehydrogenase, 3-ketosteroid-Δ(4)(5α)-dehydrogenase) from the superfamily of SDRs. For some bacteria that have been previously reported to posses a specific HSD activity, we could annotate the corresponding HSD protein. The dominating phyla that were identified to express HSDs were that of Actinobacteria, Proteobacteria, and Firmicutes. Moreover, some evolutionarily more ancient microorganisms (e.g., Cyanobacteria and Euryachaeota) were found as well. A large number of HSD-expressing bacteria constitute the normal human gastro-intestinal flora. Another group of bacteria were originally isolated from natural habitats like seawater, soil, marine and permafrost sediments. These bacteria include polycyclic aromatic hydrocarbons-degrading species such as Pseudomonas, Burkholderia and Rhodococcus. In conclusion, HSDs are found in a wide variety of microorganisms including bacteria and archaea, suggesting that steroid metabolism is an evolutionarily conserved mechanism that might serve different functions such as nutrient supply and signaling. Article from a special issue on steroids and microorganisms.

Characterization and regulation of the NADP-linked 7 alpha-hydroxysteroid dehydrogenase gene from Clostridium sordellii

A bile acid-inducible NADP-linked 7 alpha-hydroxysteroid dehydrogenase (7 alpha-HSDH) from Clostridium sordellii ATCC 9714 was purified 310-fold by ion-exchange, gel filtration, and dye-ligand affinity chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the purified enzyme showed one predominant peptide band (30,000 Da). The N-terminal sequence was determined, and the corresponding oligonucleotides were synthesized and used to screen EcoRI and HindIII genomic digests of C. sordellii. Two separate fragments (4,500 bp, EcoRI; 3,200 bp, HindIII) were subsequently cloned by ligation to pUC19 and transformation into Escherichia coli DH5 alpha-MCR. The EcoRI fragment was shown to contain a truncated 7 alpha-HSDH gene, while the HindIII fragment contained the entire coding region. E. coli clones containing the HindIII insert expressed high levels of an NADP-linked 7 alpha-HSDH. Nucleotide sequence analyses suggest that the 7 alpha-HSDH is encoded by a monocistronic transcriptional unit, with DNA sequence elements resembling rho-independent terminators located in both the upstream and downstream flanking regions. The transcriptional start site was located by primer extension analysis. Northern (RNA) blot analysis indicated that induction is mediated at the transcriptional level in response to the presence of bile acid in the growth medium. In addition, growth-phase-dependent expression is observed in uninduced cultures. Analysis of the predicted protein sequence indicates that the enzyme can be classified in the short-chain dehydrogenase group.

Molecular cloning of cDNA for rat ovarian 20 alpha-hydroxysteroid dehydrogenase (HSD1)

20 alpha-Hydroxysteroid dehydrogenase (20 alpha-HSD, EC 1.1.1.149) catalyses the conversion of progesterone into 20 alpha-dihydroprogesterone (20 alpha-OHP). Previously, we purified the enzyme (37 kDa) from rat ovary and determined its N-terminal amino acid sequence. In the present study we succeeded in cloning a full-length 20 alpha-HSD cDNA. mRNA was extracted from immature rat ovaries after successive treatment with equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG). A cDNA library was constructed in lambda ZAP. For screening, a 576 bp probe was amplified by the PCR using mixed primers based on the N-terminal sequence of 20 alpha-HSD, and labelled with [32P]dCTP. Eight positive clones were isolated from 1.2 x 10(4) recombinants. Analysis of the nucleotide sequence revealed that one clone of 1.2 kbp cDNA (pHSD12-07) contained a polyadenylation site and an open reading frame encoding 323 amino acids with the N-terminal sequence of 20 alpha-HSD. The fusion protein of pHSD12-07 produced by Escherichia coli reacted with a specific polyclonal antibody generated against rat ovarian 20 alpha-HSD. In addition, the in vitro transcription-translation product produced by Xenopus oocytes showed 20 alpha-HSD activity and Northern-blotting analysis revealed that the ovaries from normal adult rats contained a 1.2 kb mRNA. Thus we succeeded in isolating a clone encoding the full length of rat ovarian 20 alpha-HSD. The sequence showed high similarity with those of rat liver 3 alpha-hydroxysteroid dehydrogenase (3 alpha-HSD), bovine lung prostaglandin F synthase (PGFS), human liver chlordecone reductase (CDR), frog lens rho-crystallin and aldose reductases, indicating that 20 alpha-HSD belongs to the aldo-keto reductase family.

Purification and characterization of a novel dimeric 20 alpha-hydroxysteroid dehydrogenase from Tetrahymena pyriformis

Tetrahymena pyriformis was found to exhibit high NADPH-dependent 20-oxosteroid reductase activity that converted 17 alpha-hydroxyprogesterone into 17 alpha,20 alpha-dihydroxypregn-4-en-3-one. The enzyme was purified 400-fold from the cytosolic fraction. The purified enzyme with a specific activity of 6.4 mumol/min per mg of protein had an isoelectric point of 4.9 and M(r) of 68,000, and was composed of two subunits of equal size. The N-terminal sequence was determined to be LAKTVPLNDGTNFPIFGG. The enzyme reduced pregnanes and pregnanes possessing a 17 alpha-hydroxy group to a greater extent than those without the hydroxy group, and oxidized 20 alpha-hydroxy groups of the steroids in the presence of NADP+. The Km values for 17 alpha-hydroxyprogesterone and 17 alpha-hydroxypregnenolone were 2.9 and 3.4 microM respectively. Although the enzyme was inactive towards androgens and oestrogens with 3- or 17-oxo groups, it reduced several nonsteroidal carbonyl compounds and oxidized trans-benzene dihydrodiol. The enzyme activity was inhibited by synthetic oestrogens, barbiturates, aldose reductase inhibitors and quercitrin. Thus, this enzyme is a novel form of 20 alpha-hydroxysteroid dehydrogenase (EC 1.1.1.149) which structurally and functionally differs from the mammalian and bacterial enzymes.

Purification and characterization of rat ovarian 20 alpha-hydroxysteroid dehydrogenase

To investigate the regulatory mechanism of 20 alpha-hydroxysteroid dehydrogenase (20 alpha-HSD) (EC 1.1.1.149) activity in ovarian tissue, the enzyme was purified from ovaries of normal mature female rats. Column chromatography of the cytosolic fraction from ovaries on DEAE-Toyopearl 650M revealed two peaks of the 20 alpha-HSD activity at different ionic strengths. These peaks were designated HSD1 and HSD2, respectively. Each of the active fractions was further purified to homogeneity by dye-affinity chromatography using Matrex Green A and AF Red-Toyopearl. Both the fractions appeared as a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (at Mr = 33,000 under reducing conditions). Under non-reducing conditions, similar values were obtained on gel-exclusion HPLC, indicating that the enzyme fractions were single-stranded, monomeric polypeptides. Homogeneous HSD1 and HSD2 were purified 361-fold and 509-fold, respectively, and differed in their substrate preference. The two enzyme fractions had Km values of 4.75 microM and 5.16 microM for 20 alpha-dihydroprogesterone, respectively, and showed almost the same RF values on reverse-phase HPLC and free-zone capillary electrophoresis. However, amino acid composition was slightly different, i.e. lysin content was higher in HSD1 than HSD2. Thus, it was clarified that two types of 20 alpha-HSD with very similar molecular structures are present in the rat ovary.

Lipid metabolism in anaerobic ecosystems

In anaerobic ecosystems, acyl lipids are initially hydrolyzed by microbial lipases with the release of free fatty acids. Glycerol, galactose, choline, and other non-fatty acid components released during hydrolysis are fermented to volatile fatty acids by the fermentative bacteria. Fatty acids are not degraded further in the rumen or other parts of the digestive tract but are subjected to extensive biohydrogenation especially in the rumen. However, in environments such as sediments and waste digestors, which have long retention times, both long and short chain fatty acids are beta-oxidized to acetate by a special group of bacteria, the H2-producing syntrophs. Long chain fatty acids can also be degraded by alpha-oxidation. Biotransformation of bile acids, cholesterol, and steroids by intestinal microorganisms is extensive. Many rumen bacteria have specific growth requirements for fatty acids such as n-valeric, iso-valeric, 2-methylbutyric, and iso-butyric acids. Some species have requirements for C13 to C18 straight-chain saturated or monoenoic fatty acids for growth.