Renal mitochondrial ferredoxin active in 25-hydroxyvitamin D3 1 alpha-hydroxylase. Characterization of the iron-sulfur cluster using interprotein cluster transfer and electron paramagnetic resonance spectroscopy

Critical role of antioxidant programs in enzalutamide-resistant prostate cancer

Therapy resistance to second-generation androgen receptor (AR) antagonists, such as enzalutamide, is common in patients with advanced prostate cancer (PCa). To understand the metabolic alterations involved in enzalutamide resistance, we performed metabolomic, transcriptomic, and cistromic analyses of enzalutamide-sensitive and -resistant PCa cells, xenografts, patient-derived organoids, patient-derived explants, and tumors. We noted dramatically higher basal and inducible levels of reactive oxygen species (ROS) in enzalutamide-resistant PCa and castration-resistant PCa (CRPC), in comparison to enzalutamide-sensitive PCa cells or primary therapy-naive tumors respectively. Unbiased metabolomic evaluation identified that glutamine metabolism was consistently upregulated in enzalutamide-resistant PCa cells and CRPC tumors. Stable isotope tracing studies suggest that this enhanced glutamine metabolism drives an antioxidant program that allows these cells to tolerate higher basal levels of ROS. Inhibition of glutamine metabolism with either a small-molecule glutaminase inhibitor or genetic knockout of glutaminase enhanced ROS levels, and blocked the growth of enzalutamide-resistant PCa. The critical role of compensatory antioxidant pathways in maintaining enzalutamide-resistant PCa cells was validated by targeting another antioxidant program driver, ferredoxin 1. Taken together, our data identify a metabolic need to maintain antioxidant programs and a potentially targetable metabolic vulnerability in enzalutamide-resistant PCa.

Vitamin D-Mediated Hypercalcemia: Mechanisms, Diagnosis, and Treatment

Hypercalcemia occurs in up to 4% of the population in association with malignancy, primary hyperparathyroidism, ingestion of excessive calcium and/or vitamin D, ectopic production of 1,25-dihydroxyvitamin D [1,25(OH)₂D], and impaired degradation of 1,25(OH)₂D. The ingestion of excessive amounts of vitamin D₃ (or vitamin D₂) results in hypercalcemia and hypercalciuria due to the formation of supraphysiological amounts of 25-hydroxyvitamin D [25(OH)D] that bind to the vitamin D receptor, albeit with lower affinity than the active form of the vitamin, 1,25(OH)₂D, and the formation of 5,6-trans 25(OH)D, which binds to the vitamin D receptor more tightly than 25(OH)D. In patients with granulomatous disease such as sarcoidosis or tuberculosis and tumors such as lymphomas, hypercalcemia occurs as a result of the activity of ectopic 25(OH)D-1-hydroxylase (CYP27B1) expressed in macrophages or tumor cells and the formation of excessive amounts of 1,25(OH)₂D. Recent work has identified a novel cause of non-PTH-mediated hypercalcemia that occurs when the degradation of 1,25(OH)₂D is impaired as a result of mutations of the 1,25(OH)₂D-24-hydroxylase cytochrome P450 (CYP24A1). Patients with biallelic and, in some instances, monoallelic mutations of the CYP24A1 gene have elevated serum calcium concentrations associated with elevated serum 1,25(OH)₂D, suppressed PTH concentrations, hypercalciuria, nephrocalcinosis, nephrolithiasis, and on occasion, reduced bone density. Of interest, first-time calcium renal stone formers have elevated 1,25(OH)₂D and evidence of impaired 24-hydroxylase-mediated 1,25(OH)₂D degradation. We will describe the biochemical processes associated with the synthesis and degradation of various vitamin D metabolites, the clinical features of the vitamin D-mediated hypercalcemia, their biochemical diagnosis, and treatment.

Vitamin D and the kidney

The kidney is essential for the maintenance of normal calcium and phosphorus homeostasis. Calcium and inorganic phosphorus are filtered at the glomerulus, and are reabsorbed from tubular segments by transporters and channels which are regulated by 1α,25-dihydroxyvitamin (1α,25(OH)(2)D) and parathyroid hormone (PTH). The kidney is the major site of the synthesis of 1α,25(OH)(2)D under physiologic conditions, and is one of the sites of 24,25-dihydroxyvitamin D (24,25(OH)(2)D) synthesis. The activity of the 25(OH)D-1α-hydroxylase, the mixed function oxidase responsible for the synthesis of 1α,25(OH)(2)D, is regulated by PTH, 1α,25(OH)(2)D, fibroblast growth factor 23 (FGF23), inorganic phosphorus and other growth factors. Additionally, the vitamin D receptor which binds to, and mediates the activity of 1α,25(OH)(2)D, is widely distributed in the kidney. Thus, the kidney, by regulating multiple transport and synthetic processes is indispensible in the maintenance of mineral homeostasis in physiological states.

Overproduction and physical characterization of SoxR, a [2Fe-2S] protein that governs an oxidative response regulon in Escherichia coli

SoxR protein governs the soxRS (superoxide response) regulon of Escherichia coli by becoming a transcriptional activator when the cells are exposed to compounds that mediate univalent redox reactions, many of which produce superoxide as a by-product. SoxR was overproduced and purified to near homogeneity from a strain bearing an expression vector. It could bind specifically to the soxS operator even in the absence of RNA polymerase. The aerobically purified protein, which is readily autooxidized, could activate the transcription of soxS DNA even without exposure to known inducing agents. SoxR is a globular homodimer. It contains one [2Fe-2S] cluster per polypeptide chain, as demonstrated by optical and EPR spectroscopy combined with stoichiometric analysis of iron content, unpaired-electron-spin density, and reduction by dithionite. The protein is active in its oxidized ([2Fe-2S]2+) state. The presence of a prosthetic group capable of univalent redox reactions may help to explain the activation of the regulon in vivo by compounds that can mediate such reactions.

The metabolism and mechanism of action of 1,25-dihydroxyvitamin D3

Much has been learned about the formation of the active metabolite of vitamin D3, 1,25-dihydroxyvitamin D3. Information concerning its formation and catabolism has allowed a clear understanding of factors involved in the maintenance of plasma concentrations of the hormone. The effects of 1,25-dihydroxyvitamin D3 on calcium transporting cells in the intestine are marked and well defined. The tissue (intestinal tissue) is easily isolated and manipulated and hence, this is an ideal tissue in which to examine the mechanism of divalent cation transport. The mechanism by which 1,25-dihydroxyvitamin D3 brings about this effect should help in understanding sterol hormone action.

Vitamin D and skeletal tissues

It is now accepted that vitamin D is an integral part of a complex endocrine system, one with far-reaching implications in mineral metabolism. Reviews of the sources, functions and metabolism of vitamin D, as currently understood, are presented as a prelude to discussions of the role of vitamin D in calcium and phosphorous homeostatis and possible specific roles for vitamin D in mineralized tissues. Data describing a possible regulatory function for vitamin D in bone and bone protein metabolism are presented. Some of the controversy which presently exists regarding the biochemical mechanism of the action of this vitamin is discussed. Finally, the possible relationship of vitamin D and disorders of skeletal tissues is described.

Renal aminopyrine demethylation in several species determined by a sensitive radiometric method

Renal microsomal aminopyrine demethylation activities of several species were measured by a sensitive radiometric method using [dimethylamino-14C-]aminopyrine as a substrate and 2,4-dinitrophenylhydrazine as a trapping agent for the formaldehyde formed. The activity was highest in hamsters (0.75 nmol min-1 mg-1 protein) and that in rabbits, rats, mice, and guinea-pigs was 19.7, 7.0, 4.5 and 3.7%, respectively, of the hamster values. These species differences did not correlate with species differences in cytochrome P-450 content or in NADPH cytochrome c reductase activity. Aminopyrine demethylation activities in sliced renal tissues of several species were also compared. This activity was also found highest in hamsters (0.54 nmol min-1 g-1 wet tissue) and the activities in rabbits, rats, and guinea-pigs were 9.2, 1.8 and 2.5%, respectively, of the hamster values.

Subcellular mechanisms involving vitamin D

During the past 15 years a vitamin D endocrine system has been demonstrated in which vitamin D produced normally in the skin is activated first by conversion in the liver and subsequently in the kidney to a hormonal form, 1,25-(OH)2D3. The production of the hormonal form of vitamin D3, is regulated, and much has been learned regarding the molecular mechanism of the hydroxylations of vitamin D and regarding the physiologic regulators of the 25-OH-D-1-hydroxylase. Much remains to be learned regarding the mechanism whereby the 1-hydroxylase is modulated. 1,25-(OH)2D3 appears to function in the target organs of bone, intestine, kidney, and elsewhere by a nucleus-mediated process. Receptors for 1,25-(OH)2D3 have been clearly demonstrated and characterized in crude form. How the receptor and ligand interact with the nucleus is not clear, nor are the gene products that result from this interaction known. One product, a calcium binding protein, is known but its role in calcium transport is in debate. Although much has been learned in the last decade and a half, much remains to be learned regarding the molecular mechanisms whereby vitamin D brings about its remarkable changes in mineral metabolism.