Kumar, Rajiv

Abstract IER3 (formerly IEX-1) encodes a 27-kDa glycoprotein that regulates death receptor–induced apoptosis, interacts with NF-κB pathways, and increases expression rapidly in response to cellular stresses such as irradiation. Animal models, gene expression microarray experiments, and functional studies in cell lines have suggested a potential role for IER3 in oncogenesis, but, to date, no abnormalities of IER3 at the DNA level have been reported in patients with neoplasia. Here, we describe breakpoint cloning of a t(6;9)(p21;q34) translocation from a patient with a myelodysplastic syndrome (MDS), facilitated by conversion technology and array-based comparative genomic hybridization, which revealed a rearrangement translocating the IER3 coding region away from critical flanking/regulatory elements and to a transcript-poor chromosomal region, markedly decreasing expression. Using split-signal and locus-specific fluorescence in situ hybridization (FISH) probes, we analyzed 204 patients with diverse hematological malignancies accompanied by clonal chromosome 6p21 abnormalities, and found 8 additional patients with MDS with IER3 rearrangements (translocations or amplification). Although FISH studies on 157 additional samples from patients with MDS and a normal-karyotype were unrevealing, and sequencing the IER3 coding and proximal promoter regions of 74 MDS patients disclosed no point mutations, reverse transcription-PCR results suggested that dysregulated expression of IER3 is common in MDS (61% >4-fold increase or decrease in expression with decreased expression primarily in early MDS and increased expression primarily in later MDS progressing toward leukemia), consistent with findings in previous microarray experiments. These data support involvement of IER3 in the pathobiology of MDS. [Cancer Res 2009;69(19):7518–23]

Abstract Background: Urinary albumin excretion is a sensitive diagnostic and prognostic marker for renal disease. Therefore, measurement of urinary albumin must be accurate and precise. We have developed a method to quantify intact urinary albumin with a low limit of quantification (LOQ). Methods: We constructed an external calibration curve using purified human serum albumin (HSA) added to a charcoal-stripped urine matrix. We then added an internal standard, 15N-labeled recombinant HSA (15NrHSA), to the calibrators, controls, and patient urine samples. The samples were reduced, alkylated, and digested with trypsin. The concentration of albumin in each sample was determined by liquid chromatography–tandem mass spectrometry (LC-MS/MS) and linear regression analysis, in which the relative abundance area ratio of the tryptic peptides 42LVNEVTEFAK51 and 526QTALVELVK534 from albumin and 15NrHSA were referenced to the calibration curve. Results: The lower limit of quantification was 3.13 mg/L, and the linear dynamic range was 3.13–200 mg/L. Replicate digests from low, medium, and high controls (n = 5) gave intraassay imprecision CVs of 2.8%–11.0% for the peptide 42LVNEVTEFAK51, and 1.9%–12.3% for the 526QTALVELVK534 peptide. Interassay imprecision of the controls for a period of 10 consecutive days (n = 10) yielded CVs of 1.5%–14.8% for the 42LVNEVTEFAK51 peptide, and 6.4%–14.1% for the 526QTALVELVK534 peptide. For the 42LVNEVTEFAK51 peptide, a method comparison between LC-MS/MS and an immunoturbidometric method for 138 patient samples gave an R2 value of 0.97 and a regression line of y = 0.99x + 23.16. Conclusions: Urinary albumin can be quantified by a protein cleavage LC-MS/MS method using a 15NrHSA internal standard. This method provides improved analytical performance in the clinically relevant range compared to a commercially available immunoturbidometric assay.

Abstract Background: The accurate and precise measurement of urinary albumin is critical, since even minor increases are diagnostically sensitive indicators of renal disease, cardiovascular events, and risk for death. To gain insights into potential measurement biases, we systematically compared urine albumin measurements performed by LC-MS, a clinically available immunoturbidimetric assay, and size-exclusion HPLC. Methods: We obtained unused clinical urine samples from 150 patients who were stratified by degrees of albuminuria (<20 mg/L, 20–250 mg/L, >250 mg/L) as determined by the immunoturbidimetric assay used in our clinical laboratory (Roche Hitachi 912). Urine albumin was then remeasured via LC-MS and HPLC (Accumin™) assays. Results: The immunoturbidimetric assay, calibrated using manufacturer-supplied serum-derived calibrators (Diasorin), underestimated albumin compared with LC-MS. After calibration with purified HSA, this immunoturbidimetric assay correlated well with LC-MS. HPLC overestimated albumin compared with both LC-MS and immunoturbidimetry. The current LC-MS and HPLC assays both performed poorly at concentrations <20 mg/L. Conclusions: Efforts are needed to establish gold-standard traceable calibrators for clinical assays. LC-MS is a specific method to quantify albumin in native urine when concentrations exceed 20 mg/L, and therefore could be employed for standardization among assays.

Abstract Vitamin D and vitamin D metabolites such as 25-hydroxyvitamin D and 1α,25-dihydroxyvitamin D [1α,25(OH)2D3] circulate in the serum of fish. The receptor for 1α,25(OH)2D3 (VDR) has previously been cloned from fish intestine, and ligand binding assays have shown the presence of the VDR in the gills, intestine, and liver of fish. Using immunohistochemical methods with specific antibodies against the VDR, we now report that the VDR is widely expressed in tissues of the adult male and female zebrafish, Danio rerio, specifically in epithelial cells of gills, tubular cells of the kidney, and absorptive cells in the intestine. Additionally, the VDR is expressed in the skin, the olfactory organ, the retina, brain, and spinal cord. Sertoli cells of the testis, oocytes, acinar cells of the pancreas, hepatocytes, and bile duct epithelial cells express substantial amounts of the receptor. Osteoblast-like cells and chondrocytes also express VDR. Preimmune serum and antiserum preadsorbed with Danio VDR protein fails to detect VDR in the same tissues. The VDR is also present in the developing eye, brain, and otic vesicle of 48- and 96-h postfertilization zebrafish embryos. Parenteral administration of 1α,25(OH)2D3 increases concentrations of VDR in intestinal epithelial cells but not in epithelial cells of the gills. Lithocholic acid, however, does not alter concentrations of VDR after parenteral administration. The data suggest that VDR is widely distributed in tissues of the zebrafish, D. rerio, and is likely to play important roles in epithelial transport, bone, and endocrine function. Furthermore, concentrations of the receptor seem to be regulated by its ligand, 1α,25-dihydroxyvitamin D but not by lithocholic acid. Zebrafish may serve as a useful model in which to assess the function of the VDR in diverse tissues.

The mechanisms by which phosphorus homeostasis is preserved in mammals are not completely understood. We demonstrate the presence of a mechanism by which the intestine detects the presence of increased dietary phosphate and rapidly increases renal phosphate excretion. The mechanism is of physiological relevance because it maintains plasma phosphate concentrations in the normal range after ingestion of a phosphate-containing meal. When inorganic phosphate is infused into the duodenum, there is a rapid increase in the renal fractional excretion of phosphate (FE Pi). The phosphaturic effect of intestinal phosphate is specific for phosphate because administration of sodium chloride does not elicit a similar response. Phosphaturia after intestinal phosphate administration occurs in thyro-parathyroidectomized rats, demonstrating that parathyroid hormone is not essential for this effect. The increase in renal FE Pi in response to the intestinal administration of phosphate occurs without changes in plasma concentrations of phosphate (filtered load), parathyroid hormone, FGF-23, or secreted frizzled related protein-4. Denervation of the kidney does not attenuate phosphaturia elicited after intestinal phosphate administration. Phosphaturia is not elicited when phosphate is instilled in other parts of the gastrointestinal tract such as the stomach. Infusion of homogenates of the duodenal mucosa increases FE Pi, which demonstrates the presence of one or more substances within the intestinal mucosa that directly modulate renal phosphate reabsorption. Our experiments demonstrate the presence of a previously unrecognized phosphate gut–renal axis that rapidly modulates renal phosphate excretion after the intestinal administration of phosphate.

Abstract We report here the first association between vitamin D–resistant rickets, alopecia, and type 1 diabetes in a child with compound heterozygous mutations in the VDR gene. Transfection studies suggest dissociated effects of VDR gene mutations on the regulation of genes involved in vitamin D metabolism and dendritic cell maturation. Introduction: Whereas vitamin D may play a role in the immune tolerance process, no patient has been reported to associate hereditary vitamin D–resistant rickets (HVDRR) and an autoimmune disease, and no attempt has been made to delineate the outcome of mutations of the vitamin D receptor (VDR) on the transcription of genes controlling immune tolerance. Materials and Methods: The VDR gene was analyzed in a child with vitamin D–resistant rickets, total alopecia, and early childhood–onset type 1 diabetes. Patient's fibroblasts and COS-7 cells transfected with wildtype or mutant VDRs were studied for ligand-binding capacity, transactivation activity using two gene promoters [CYP-24, a classical 1,25(OH)2D3-responsive gene, and relB, a critical NF-κB component for regulation of dendritic cell differentiation], VDR-RXR heterodimers association to CYP 24 VDREs by gel mobility shift assays, and co-activator binding by Glutathione-S-transferase pull-down assays. Results: Two novel compound heterozygous mutations (L263R and R391S) were identified in the VDR ligand-binding domain in this child. Both mutations significantly impaired VDR ligand-binding capacity but had dissociated effects on CYP-24 and RelB promoter responses to vitamin D. CYP 24 response binding to SRC-1 and RXR-heterodimer binding to CYP24 VDREs were abolished in L263R mutants but normal or partially altered in R391S mutants. In the opposite, RelB responses to vitamin D were close to normal in L263R mutants but abolished in R391S mutants. Conclusions: We report the first clinical association between HVDRR, total alopecia, and early childhood–onset type 1 diabetes. Mutations in the VDR ligand-binding domain may hamper the 1,25(OH)2D3–mediated relB responses, an effect that depends on the site of the VDR mutation and cannot be anticipated from VDR ligand-binding ability or CYP-24 response. Based on these results, we propose to survey the immune function in patients with HVDRR, including those with moderate features of rickets.

To determine whether receptor-mediated endocytosis occurs in vasopressin-responsive cells, we developed a model system using synthetic fluorescent-labeled vasopressin analogs and A10 (smooth muscle) and LLC-PK1 (kidney epithelial) cells in culture; these cell lines express V1 and V2 vasopressin cell surface receptor types, respectively. We used epifluorescence microscopy to examine the binding, internalization, and intracellular destination of [1-(2-mercapto)propionic acid,8-lysine-N6-carboxytetramethylrhodamine] vasopressin (R-MLVP) and [1-(2-mercapto)propionic acid,8-lysine-N6-carboxyfluorescein]vasopressin (F-MLVP) in these cells. The rhodamine-labeled fluorescent vasopressin analog, R-MLVP, initially bound in a diffuse manner at the cell surface of both A10 and LLC-PK1 cells and could be displaced by excess unlabeled [8-arginine]vasopressin. After incubation at 37 degrees C, bound ligand rapidly aggregated into small clusters or patches, which were internalized in a manner consistent with receptor-mediated endocytosis. Subsequent processing of internalized ligand-receptor complexes appeared to differ between A10 and LLC-PK1 cells. In the case of LLC-PK1 cells, ligand was delivered to a tightly focused lysosome compartment in the perinuclear region of the cell, and receptor molecules were replenished at the cell surface. The lysosomal location of ligand was supported by the quenching of fluorescence in the internalized vesicles when F-MLVP was used as a fluorescent tracer. In the case of A10 cells, ligand became localized to a vesicular compartment and reappearance of receptor at the cell surface was limited. Our data are consistent with the occurrence of receptor-mediated endocytosis of vasopressin in cells with V1 and V2 receptors.