Parvalbumin in rat kidney. Purification and localization

The rise and fall of novel renal magnesium transporters

Body Mg2+ balance is finely regulated in the distal convoluted tubule (DCT), where a tight interplay among transcellular reabsorption, mitochondrial exchange, and basolateral extrusion takes place. In the last decades, several research groups have aimed to identify the molecular players in these processes. A multitude of proteins have been proposed to function as Mg2+ transporter in eukaryotes based on phylogenetic analysis, differential gene expression, and overexpression studies. However, functional evidence for many of these proteins is lacking. The aim of this review is, therefore, to critically reconsider all putative Mg2+ transporters and put their presumed function in context of the renal handling of Mg2+. Sufficient experimental evidence exists to acknowledge transient receptor potential melastatin (TRPM) 6 and TRPM7, solute carrier family 41 (SLC41) A1 and SLC41A3, and mitochondrial RNA splicing 2 (MRS2) as Mg2+ transporters. TRPM6/7 facilitate Mg2+ influx, SLC41A1 mediates Mg2+ extrusion, and MRS2 and SLC41A3 are implicated in mitochondrial Mg2+ homeostasis. These proteins are highly expressed in the DCT. The function of cyclin M (CNNM) proteins is still under debate. For the other proposed Mg2+ transporters including Mg2+ transporter subtype 1 (MagT1), nonimprinted in Prader-Willi/Angelman syndrome (NIPA), membrane Mg2+ transport (MMgT), Huntingtin-interacting protein 14 (HIP14), and ATP13A4, functional evidence is limited, or functions alternative to Mg2+ transport have been suggested. Additional characterization of their Mg2+ transport proficiency should be provided before further claims about their role as Mg2+ transporter can be made.

Magnesium in man: implications for health and disease

Magnesium (Mg(2+)) is an essential ion to the human body, playing an instrumental role in supporting and sustaining health and life. As the second most abundant intracellular cation after potassium, it is involved in over 600 enzymatic reactions including energy metabolism and protein synthesis. Although Mg(2+) availability has been proven to be disturbed during several clinical situations, serum Mg(2+) values are not generally determined in patients. This review aims to provide an overview of the function of Mg(2+) in human health and disease. In short, Mg(2+) plays an important physiological role particularly in the brain, heart, and skeletal muscles. Moreover, Mg(2+) supplementation has been shown to be beneficial in treatment of, among others, preeclampsia, migraine, depression, coronary artery disease, and asthma. Over the last decade, several hereditary forms of hypomagnesemia have been deciphered, including mutations in transient receptor potential melastatin type 6 (TRPM6), claudin 16, and cyclin M2 (CNNM2). Recently, mutations in Mg(2+) transporter 1 (MagT1) were linked to T-cell deficiency underlining the important role of Mg(2+) in cell viability. Moreover, hypomagnesemia can be the consequence of the use of certain types of drugs, such as diuretics, epidermal growth factor receptor inhibitors, calcineurin inhibitors, and proton pump inhibitors. This review provides an extensive and comprehensive overview of Mg(2+) research over the last few decades, focusing on the regulation of Mg(2+) homeostasis in the intestine, kidney, and bone and disturbances which may result in hypomagnesemia.

Isolation, characterisation and cDNA sequencing of a new form of parvalbumin from carp semen

Parvalbumins (Pv) are calcium-binding proteins present mainly in the muscle and nervous system where they act as a Ca2+ buffer. Our previous work demonstrated the presence of Pv-I in carp semen and indicated the presence of a second Pv (Pv-II). The purpose of the present work was to identify, purify and determine the full-length cDNA sequence of Pv-II from carp testis. Pv-II from seminal plasma was purified by ion-exchange chromatography (IEC) and preparative electrophoresis, while the Pv-II from spermatozoa was purified by IEC, gel filtration and preparative electrophoresis. The purified Pv-II was submitted to an analysis of molecular mass, isoelectric point (pI), amino-acid sequence and oligomerisation ability. The amino-acid sequence was used to construct primers and obtain the full-length cDNA sequence of seminal-specific Pv-II from carp testis. Analysis of the cDNA sequence indicated that carp-testis Pv-II was distinct from carp-muscle parvalbumins. Pv-II was distinct from Pv-I regarding sequence, molecular mass and pI. Both parvalbumins had the ability to form oligomers or to bind to other proteins. Carp seminal plasma had a protective effect against parvalbumin oligomerisation. Pv-II underwent post-translational modification such as n-acetylation and cysteinylation. The present study is the first to report the full-length cDNA sequence of parvalbumin from carp testis.

Epidermal growth factor-mediated activation of the ETS domain transcription factor Elk-1 requires nuclear calcium

Cytosolic and nuclear Ca(2+) have been shown to differentially regulate transcription. However, the impact of spatially distinct Ca(2+) signals on mitogen-activated protein kinase-mediated gene expression remains unknown. Here we investigated the role of nuclear and cytosolic Ca(2+) signals in epidermal growth factor (EGF)-induced transactivation of the ternary complex factor Elk-1 using a GAL4-Elk-1 construct. EGF increased Ca(2+) in both the nucleus and cytosol of HepG2 or 293 cells. Pretreatment with the intracellular Ca(2+) chelator bis(2-aminophenyl)ethyleneglycol-N,N,N',N'-tetraacetic acid significantly reduced EGF-induced transactivation of Elk-1, indicating that EGF-stimulated Elk-1 transcriptional activity is dependent on intracellular Ca(2+). To determine the relative contribution of nuclear and cytosolic Ca(2+) signals during EGF-mediated Elk-1 transactivation, Ca(2+) signals in either compartment were selectively impaired by targeted expression of the Ca(2+)-binding protein parvalbumin to either the nucleus or cytosol. Suppression of nuclear but not cytosolic Ca(2+) signals inhibited EGF-induced transactivation of Elk-1. However, suppression of nuclear Ca(2+) signals did not affect the ability of ERK either to become phosphorylated or to undergo translocation to the nucleus in response to EGF. Elk-1 phosphorylation and nuclear localization following EGF stimulation were also unaffected by suppressing nuclear Ca(2+) signals. These results suggest that nuclear Ca(2+) is required for EGF-mediated transcriptional activation of Elk-1 and that phosphorylation of Elk-1 alone is not sufficient to induce its transcriptional activation in response to EGF. Thus, subcellular targeting of parvalbumin reveals a distinct role for nuclear Ca(2+) signals in mitogen-activated protein kinase-mediated gene transcription.

Parvalbumin is constantly expressed in chromophobe renal carcinoma

Chromophobe renal carcinoma is composed of neoplastic cell showing several features similar to those found in the intercalated cells of the collecting ducts. Because the distal nephron expresses calcium-binding proteins playing a role in calcium homeostasis, we reasoned that these proteins could be expressed by chromophobe carcinoma and therefore represent a diagnostic marker. We studied the immunohistochemical expression of different calcium-binding proteins (parvalbumin, calbindin-D28K, and calretinin) in 140 renal tumors, including 75 conventional (clear cell) carcinomas, 32 chromophobe carcinomas, 17 papillary renal cell carcinomas, and 16 oncocytomas. Parvalbumin was strongly positive in all primary chromophobe carcinomas and in one pancreatic metastasis; it was positive in 11 of 16 oncocytomas and absent in conventional (clear cell) and papillary renal cell carcinomas, either primary or metastatic. Calbindin-D28K and calretinin were negative in all tumors, with the exception of two chromophobe carcinomas, four oncocytomas, and two papillary renal cell carcinomas showing inconspicuous calretinin expression. Our data demonstrate that parvalbumin may be a suitable marker for distinguishing primary and metastatic chromophobe carcinoma from conventional (clear cell) and papillary renal cell carcinoma. Moreover, they suggest a relationship between chromophobe renal carcinoma and renal oncocytoma and indicate that chromophobe carcinoma exhibits differentiation toward the collecting-duct phenotype.

Parvalbumin is expressed in normal and pathological human parathyroid glands

The parathyroid glands are of major importance in calcium homeostasis. Small changes in the plasma calcium (Ca2+) concentration induce rapid changes in parathyroid hormone (PTH) secretion to maintain the extracellular Ca2+ levels within the physiological range. Extracellular Ca2+ concentration is continuously measured by a G-protein-coupled Ca2+-sensing receptor, which influences the expression and secretion of PTH. The mechanism of signal transduction from receptor sensing to PTH secretion is not well understood, but changes in PTH secretion are tightly linked to changes in the cytosolic Ca2+ concentration. Using immunohistochemistry and Western blot analysis, we detected the EF Ca2+ binding protein parvalbumin (PV) in normal and in hyperplastic and adenomatous human parathyroid glands. The strongest PV signal was present in chief cells and water clear cells, whereas in oxyphilic cells only a weak signal was observed. Immunohistochemistry and in situ hybridization of the PTH indicated a co-localization of PV and PTH in the same cell types. Because changes in the cytosolic Ca2+ concentration are believed to influence the process of PTH secretion, a possible role of PV as a modulator of this Ca2+ signaling is envisaged.

Parvalbumin expression during developmental differentiation of the rat ovary

Parvalbumin (PV) is a high-affinity Ca(2+)-binding protein which is expressed in a limited number of vertebrates tissues and restricted to a few distinct cell types. It has been shown by biochemical methods to be present in the adult rat ovary, but cellular localizations or developmental appearance have not been described until now. This study describes the presence of PV and its transcripts, analyzed by immunohistochemistry and in situ hybridization, respectively, during the postnatal development of the rat ovary: 13 developmental stages between day 1 and day 83 were examined. In ovaries 1-16 days old, neither PV mRNA nor PV was observed in any caaaaaaaaaaaaaay. By contrast, starting from day 18 postpartum, both PV mRNA and PV were detected in low amounts, simultaneously with the onset of differentiation of secondary intestitial gland cells in the ovarian interfollicular stroma. PV and its transcripts were primarily detected in conspicuous patches of interstitial gland tissue and in the differentiated thecal cells around the large follicles, and PV appeared to be fully expressed 33 days after birth. The parallel time courses of PV mRNA and PV accumulation during developmental differentiation, and the appearance of a steroid-producing cellular phenotype as well as the strict cellular colocalization of these two features, strongly suggest involvement of PV in the steroid metabolism of these cells, as earlier proposed for the Leydig cells of the testis. According to this hypothesis, we also show that suppression of gonadotrophic hormone production by hypophysectomy of adult rats totally suppresses PV production in parallel with the disappearance of the morphological features typical of steroid-producing cells in the remaining interstitial tissue of the ovary.

Parvalbumin-immunoreactive material in the kidney of Xenopus laevis

Parvalbumin-immunoreactive material has been localized in various parts of the Xenopus kidney. Ciliated epithelia in the neck segment, the intermediate segment and in the peritoneal funnel, epithelial cells intermingled among flask cells in the connecting tubule, and cells in the proximal and distal tubules cells were labelled. Renal corpuscle and collecting duct cells did not exhibit parvalbumin immunoreactivities. Western-blot analysis of kidney homogenates indicated various isoforms of parvalbumin-immunoreactive proteins.

Parvalbumin increases in the caudate putamen of rats with vitamin D hypervitaminosis

The influence of chronic vitamin D3 application on the concentration of the four calcium-binding proteins parvalbumin, the 28-kDa calbindin-D, calmodulin, and S-100 was studied in various brain regions and in the kidney. Young rats were administered daily 20,000 international units of vitamin D3 per kg (body weight) over a period of 4 months. This chronic treatment resulted in a clinically mild hypervitaminosis that did not affect the content of calmodulin, the 28-kDa calbindin-D, and S-100. Also the concentration of parvalbumin in the cerebral cortex, hippocampus, and kidney remained unchanged. On the other hand, parvalbumin was increased about 50% in the caudate putamen of hypervitaminotic animals as compared to controls. Our results indicate that the metabolism of parvalbumin in the caudate putamen can be influenced by variations of the blood level of this steroid hormone.