Advances in Vitamin D Receptor Function and Evolution Based on the 3D Structure of the Lamprey Ligand-Binding Domain

1α,25-dihydroxyvitamin D3 (1,25D₃) regulates many physiological processes in vertebrates by binding to the vitamin D receptor (VDR). Phylogenetic analysis indicates that jawless fishes are the most basal vertebrates exhibiting a VDR gene. To elucidate the mechanism driving VDR activation during evolution, we determined the crystal structure of the VDR ligand-binding domain (LBD) complex from the basal vertebratePetromyzon marinus, sea lamprey (lVDR). Comparison of three-dimensional crystal structures of the lVDR-1,25D₃ complex with higher vertebrate VDR-1,25D₃ structures suggests that 1,25D₃ binds to lVDR similarly to human VDR, but with unique features for lVDR around linker regions between H11 and H12 and between H9 and H10. These structural differences may contribute to the marked species differences in transcriptional responses. Furthermore, residue co-evolution analysis of VDR across vertebrates identifies amino acid positions in H9 and the large insertion domain VDR LBD specific as correlated.

Cytosolic sequestration of the vitamin D receptor as a therapeutic option for vitamin D-induced hypercalcemia

The bioactive vitamin D₃, 1α,25(OH)₂D₃, plays a central role in calcium homeostasis by controlling the activity of the vitamin D receptor (VDR) in various tissues. Hypercalcemia secondary to high circulating levels of vitamin D₃ leads to hypercalciuria, nephrocalcinosis and renal dysfunctions. Current therapeutic strategies aim at limiting calcium intake, absorption and resorption, or 1α,25(OH)₂D₃ synthesis, but are poorly efficient. In this study, we identify WBP4 as a new VDR interactant, and demonstrate that it controls VDR subcellular localization. Moreover, we show that the vitamin D analogue ZK168281 enhances the interaction between VDR and WBP4 in the cytosol, and normalizes the expression of VDR target genes and serum calcium levels in 1α,25(OH)₂D₃-intoxicated mice. As ZK168281 also blunts 1α,25(OH)₂D₃-induced VDR signaling in fibroblasts of a patient with impaired vitamin D degradation, this VDR antagonist represents a promising therapeutic option for 1α,25(OH)₂D₃-induced hypercalcemia.

Current therapeutic strategies for vitamin D-induced hypercalcemia are poorly efficient. Here the authors identify a new interaction between the vitamin D receptor (VDR) and WBP4 controlling the subcellular localization of VDR and show that ZK168281, a VDR antagonist, enhances the interaction between VDR and WBP4 blunting VDR signalling and normalizing calcium levels in vitamin D-intoxicated mice.

Molecular determinants of MED1 interaction with the DNA bound VDR-RXR heterodimer

The MED1 subunit of the Mediator complex is an essential coactivator of nuclear receptor-mediated transcriptional activation. While structural requirements for ligand-dependent binding of classical coactivator motifs of MED1 to numerous nuclear receptor ligand-binding domains have been fully elucidated, the recognition of the full-length or truncated coactivator by full nuclear receptor complexes remain unknown. Here we present structural details of the interaction between a large part of MED1 comprising its structured N-terminal and the flexible receptor-interacting domains and the mutual heterodimer of the vitamin D receptor (VDR) and the retinoid X receptor (RXR) bound to their cognate DNA response element. Using a combination of structural and biophysical methods we show that the ligand-dependent interaction between VDR and the second coactivator motif of MED1 is crucial for complex formation and we identify additional, previously unseen, interaction details. In particular, we identified RXR regions involved in the interaction with the structured N-terminal domain of MED1, as well as VDR regions outside the classical coactivator binding cleft affected by coactivator recruitment. These findings highlight important roles of each receptor within the heterodimer in selective recognition of MED1 and contribute to our understanding of the nuclear receptor-coregulator complexes.

Quercetin potentializes the respective cytotoxic activity of gemcitabine or doxorubicin on 3D culture of AsPC-1 or HepG2 cells, through the inhibition of HIF-1α and MDR1

The impact of cancer on lifespan is significantly increasing worldwide. Enhanced activity of drug efflux pumps and the incidences of the tumor microenvironment such as the apparition of a hypoxic gradient inside of the bulk tumor, are the major causes of chemotherapy failure. For instance, expression of Hypoxia-inducible factor (HIF-1α) has been associated with metastasis, resistance to chemotherapy and reduced survival rate. One of the current challenges to fight against cancer is therefore to find new molecules with therapeutic potential that could overcome this chemoresistance. In the present study, we focused on the bioactive plant flavonoid quercetin, which has strong antioxidant and anti-proliferative properties. We examined the efficacy of combined treatments of quercetin and the anti-cancer drugs gemcitabine and doxorubicin, known to specifically act on human pancreatic and hepatic cancer cells, respectively. Moreover, our study aimed to investigate more in-depth the implication of the multidrug transporter MDR1 and HIF-1α n chemoresistance and if quercetin could act on the activity of the drug efflux pumps and the hypoxia-associated effects. We observed that the anti-cancer drugs, were more effective when administered in combination with quercetin, as shown by an increased percentage of dead cells up to 60% in both 2D and 3D cultures. In addition, our results indicated that the combination of anti-cancer drugs and quercetin down-regulated the expression of HIF-1α and increased the expression levels of the regulator of apoptosis p53. Moreover, we observed that quercetin could inhibit the efflux activity of MDR1. Finally, our in vitro study suggests that the efficiency of the chemotherapeutic activity of known anti-cancer drugs might be significantly increased upon combination with quercetin. This flavonoid may therefore be a promising pharmacological agent for novel combination therapy since it potentializes the cytotoxic activity of gemcitabine and doxorubicin on by targeting the chemoresistance developed by the pancreatic and liver cancer cells respectively.

Structural Analysis of VDR Complex with ZK168281 Antagonist

Vitamin D receptor (VDR) antagonists prevent the VDR activation function helix 12 from folding into its active conformation, thus affecting coactivator recruitment and antagonizing the transcriptional regulation induced by 1α,25-dihydroxyvitamin D3. Here, we report the crystal structure of the zebrafish VDR ligand-binding domain in complex with the ZK168281 antagonist, revealing that the ligand prevents optimal folding of the C-terminal region of VDR. This interference was confirmed by hydrogen-deuterium exchange mass spectrometry (HDX-MS) in solution.

Blood Transfusions in Dogs and Cats Receiving Hemodialysis: 230 Cases (June 1997-September 2012)

Background

Multiple factors exist that contribute to anemia in dogs and cats receiving hemodialysis, can necessitate transfusion.

Objectives

To describe blood product usage in dogs and cats with acute and chronic kidney disease that were treated with intermittent hemodialysis to determine risk factors associated with the requirement for blood product transfusion.

Animals

83 cats and 147 dogs undergoing renal replacement therapy at the Animal Medical Center for acute or chronic kidney disease.

Methods

Retrospective medical record review of all dogs and cats receiving renal replacement therapy for kidney disease, from June 1997 through September 2012.

Results

Blood products (whole blood, packed RBCs, or stromal‐free hemoglobin) were administered to 87% of cats and 32% of dogs. The number of dialysis treatments was associated with the requirement for transfusion in cats (adjusted OR 2.21, 95% CI 1.13, 4.32), but not in dogs (adjusted OR 0.98, 95% CI 0.95, 1.03). Administration of a blood product was associated with a higher likelihood of death in dogs (OR 3.198, 95% CI 1.352, 7.565; P = .0098), but not in cats (OR 1.527, 95% CI 0.5404, 4.317, P = .2).

Conclusions and Clinical Importance

Veterinary hospitals with a hemodialysis unit should have reliable and rapid access to safe blood products in order to meet the needs of dogs and cats receiving dialysis.

The use of darbepoetin to stimulate erythropoiesis in anemia of chronic kidney disease in cats: 25 cases

BACKGROUND

Anemia is present in 30-65% in cats with chronic kidney disease (CKD) and few long-term treatment options exist. Darbepoetin is effective in treating anemia of kidney disease in humans and may be used in cats.

HYPOTHESIS/OBJECTIVE

To evaluate the use of darbepoetin, a recombinant analog of human erythropoietin, to stimulate erythropoiesis, and to effectively treat anemia of kidney disease in cats.

ANIMALS

Twenty-five of 66 cats that received ≥ 2 doses of darbepoetin at the Animal Medical Center between January 2005 and December 2009 were included in this study.

METHODS

Cats were included in the study if they received darbepoetin and follow-up data were available for at least 56 days and had CKD as a primary clinical diagnosis. Cats were excluded if they were treated with darbepoetin but did not have kidney disease. Response to treatment was defined as reaching or exceeding a target packed red blood cell volume or hematocrit of 25%.

RESULTS

Fourteen of 25 cats responded. Thirteen of those 14 cats received a dosage of 1 μg/kg/wk or higher. Presumptive adverse effects included vomiting, hypertension, seizures, and fever.

CONCLUSIONS AND CLINICAL RELEVANCE

Darbepoetin is effective for treatment of anemia of kidney disease in cats. Pure red cell aplasia appears to be less common with darbepoetin than with epoetin usage.

[Primary choriocarcinoma of the cervix]

We report a case of primary choriocarcinoma of the cervix in which the patient died 9 months later. The treatment consisted to administer 5 cycles of chemotherapy pre-operatively and a colpohysterectomy. The pathogeny is a cervical migration of trophoblastics cells after a normal or molar pregnancy which degenerate to choriocarcinoma.