PubTransformer

A site to transform Pubmed publications into these bibliographic reference formats: ADS, BibTeX, EndNote, ISI used by the Web of Knowledge, RIS, MEDLINE, Microsoft's Word 2007 XML.

Dana Cucu - Top 30 Publications

N-glycosylation of the transient receptor potential melastatin 8 channel is altered in pancreatic cancer cells.

Transient receptor potential melastatin 8 (TRPM8), a membrane ion channel, is activated by thermal and chemical stimuli. In pancreatic ductal adenocarcinoma, TRPM8 is required for cell migration, proliferation, and senescence and is associated with tumor size and pancreatic ductal adenocarcinoma stages. Although the underlying mechanisms of these processes have yet to be described, this cation-permeable channel has been proposed as an oncological target. In this study, the glycosylation status of the TRPM8 channel was shown to affect cell proliferation, cell migration, and calcium uptake. TRPM8 expressed in the membrane of the Panc-1 pancreatic tumoral cell line is non-glycosylated, whereas human embryonic kidney cells transfected with human TRPM8 overexpress a glycosylated protein. Moreover, our data suggest that Ca(2+) uptake is modulated by the glycosylation status of the protein, thus affecting cell proliferation.

Effects of Cd2+ on the epithelial Na+ channel (ENaC) investigated by experimental and modeling studies.

The function of the epithelial Na+ channel from the apical membrane of many Na+ transporting epithelia is modulated by various chemical compounds from the extracellular space, such as heavy metals, protons or chloride ions. We have studied the effect of extracellular Cd2+ on the function of the epithelial Na+ channel (ENaC) in heterologously expressed Xenopus laevis oocytes and Na+-transporting epithelia. We assayed channel function as the amiloride-sensitive sodium current (I(Na)). Cd2+ rapidly and voltage-independently inhibited INa in oocytes expressing αβγ Xenopus ENaC (xENaC). The extracellular Cd2+ inhibited Na+ transport and showed no influence on ENaC trafficking, as revealed by concomitant measurements of the transepithelial current, conductance and capacitance in Na+-transporting epithelia. Instead, amiloride inhibition was noticeably diminished in the presence of Cd2+ on the apical membrane. Using molecular modeling approaches, we describe the amiloride binding sites in rat and xENaC structures, and we present four putative binding sites for Cd2+. These results indicate that ENaC functions as a sensor for external Cd2+.

Characterization of functional transient receptor potential melastatin 8 channels in human pancreatic ductal adenocarcinoma cells.

Recently, the transient receptor potential melastatin 8 (TRPM8) channel has emerged as a putative biomarker for pancreatic ductal adenocarcinoma (PDA). This study aimed to evaluate the expression of TRPM8 and its modulation by specific agonists and antagonists in PDA cells.

Low doses of cadmium chloride and methallothionein-1-bound cadmium display different accumulation kinetics and induce different genes in cells of the human nephron.

The present study was conducted to investigate the renal tubular handling of inorganic cadmium (Cd(2+)) by exposing primary human tubular cell cultures to physiologically relevant doses of cadmium chloride (CdCl(2)). Furthermore, the cellular accumulation of Cd(2+) was compared to that of metallothionein-1-bound Cd (Cd7MT-1). Finally, this study aimed to investigate the effect of the accumulation of Cd (both Cd(2+) and Cd7MT-1) in renal cells on the expression of genes relevant to nephrotoxic processes.

Effect of calcium oxalate on renal cells as revealed by real-time measurement of extracellular oxidative burst.

Calcium oxalate is one of the main constituents of kidney stones and has a proved deleterious effect on renal cells that is mediated by oxidative stress. However, the subcellular source of this oxidative stress, and whether it is extending to the extracellular space or not, is still disputed. Therefore, an electrochemical superoxide biosensor was constructed, positioned above A6 renal cells, and used to measure in real-time the extracellular oxidative burst following addition of calcium oxalate crystals. It was observed that A6 cells do secrete superoxide into their extracellular space in few minutes after encountering calcium oxalate crystals. The amount of released superoxide peaks at about 20 min. Superoxide is cleared away from the extracellular space after approximately 3h. Superoxide secretion depends on the presence of superoxide-scavenging enzyme superoxide dismutase, the age of the cells, the amount of calcium oxalate crystals, and the temperature. Moreover, the effect of calcium oxalate crystals was mimicked by phorbol 12-myristate 13-acetate. The developed sensing system can be a useful tool for biologists investigating nephrolithiasis at cellular level.

Opposite effects of Ni2+ on Xenopus and rat ENaCs expressed in Xenopus oocytes.

The epithelial Na+ channel (ENaC) is modulated by various extracellular factors, including Na+, organic or inorganic cations, and serine proteases. To identify the effect of the divalent Ni2+ cation on ENaCs, we compared the Na+ permeability and amiloride kinetics of Xenopus ENaCs (xENaCs) and rat ENaCs (rENaCs) heterologously expressed in Xenopus oocytes. We found that the channel cloned from the kidney of the clawed toad Xenopus laevis [wild-type (WT) xENaC] was stimulated by external Ni2+, whereas the divalent cation inhibited the channel cloned from the rat colon (WT rENaC). The kinetics of amiloride binding were determined using noise analysis of blocker-induced fluctuation in current adapted for the transoocyte voltage-clamp method, and Na+ conductance was assessed using the dual electrode voltage-clamp (TEVC) technique. The inhibitory effect of Ni2+ on amiloride binding is not species dependent, because Ni2+ decreased the affinity (mainly reducing the association rate constant) of the blocker in both species in competition with Na+. Importantly, using the TEVC method, we found a prominent difference in channel conductance at hyperpolarizing voltage pulses. In WT xENaCs, the initial ohmic current response was stimulated by Ni2+, whereas the secondary voltage-activated current component remained unaffected. In WT rENaCs, only a voltage-dependent block by Ni2+ was obtained. To further study the origin of the xENaC stimulation by Ni2+, and based on the rationale of the well-known high affinity of Ni2+ for histidine residues, we designed alpha-subunit mutants of xENaCs by substituting histidines that were expressed in oocytes, together with WT beta- and gamma-subunits. Changing His215 to Asp in one putative amiloride-binding domain (WYRFHY) in the extracellular loop between Na+ channel membrane segments M1 and M2 had no influence on the stimulatory effect of Ni2+, and neither did complete deletion of this segment. Next, we mutated His416 flanked by His411 and Cys417, a unique site for possible heavy metal ion chelation, and, with this quality, most proximal (approximately 100 amino acids upstream of the second putative amiloride binding site at the pore entrance), was found localized at M2. Replacing His416 with arginine, aspartate, tyrosine, and alanine clearly affected amiloride binding in all cases, as well as Na+ conductance, as expressed in the xENaC current-voltage relationship, especially with regard to aspartate and tyrosine. However, similarly to those obtained with the WYRFHY stretch, none of these mutations could either abolish the stimulating effect of Ni2+ or reverse it to an inhibitory type.

The transoocyte voltage clamp: a non-invasive technique for electrophysiological experiments with Xenopus laevis oocytes.

We developed a non-invasive technique for electrophysiological investigations of ion transport proteins endogenously or heterologously expressed in Xenopus laevis oocytes. We named this technique the transoocyte voltage clamp (TOVC). Whereas in the classical two-microelectrode voltage-clamp (TEVC) technique, the oocyte is impaled with two glass microelectrodes, we mount the egg in a modified Ussing chamber as used for transepithelial electrophysiological studies. The oocyte is introduced in a container that is positioned between the two chamber halves. Proper fixation of the oocyte in the aperture of the container is accomplished under a stereo binocular microscope and the electrical seal between the oocyte and the container is achieved with silicon grease. The new method allows measurement of transoocyte currents and conductances as well as the recording of membrane impedance and the fluctuation analysis of ion currents. We studied a K+ channel that resembles the inward rectifier K+ channel endogenously expressed in Xenopus laevis oocytes. K+ currents were obtained by exposing one side of the oocyte to K(+)-containing solutions and by the application of different voltages. Adding Cs+ and Ba2+ inhibited these currents. The analysis of the fluctuation in current demonstrated a Lorentzian component in the power density spectrum. With the transoocyte voltage clamped to zero, the corner frequency (fc) was 61+/-1.7 Hz. Imposed positive transoocyte potentials caused a downward shift of fc. These findings are consistent with previous data obtained using the TEVC technique, and extend the characterization of the channel with kinetic data obtained from noise analysis.

Rat ENaC expressed in Xenopus laevis oocytes is activated by cAMP and blocked by Ni(2+).

We used oocytes of the South African clawed toad Xenopus laevis to express the three subunits of the epithelial Na(+) channel from rat distal colon (rENaC). We combined conventional dual-microelectrode voltage-clamp with continuous capacitance (C(m)) measurements and noise analysis to evaluate the effects of cAMP and Ni(2+) on rENaC. Control oocytes or rENaC-expressing oocytes exhibited no spontaneous fluctuations in current. However, in rENaC-expressing oocytes amiloride induced a marked plateau-shaped rise of the power density spectra. Recordings using four different concentrations of amiloride revealed that the blocker-channel interactions were of the first order. A cocktail of the membrane permeant cAMP analogue chlorophenylthio-cAMP and IBMX (cAMP cocktail) increased amiloride-sensitive current (I(ami)) and conductance (G(ami)). Furthermore, C(m) was also increased following cAMP application, indicating an increase in plasma membrane surface area. Noise analysis showed that cAMP increased the number of active channels in the oocyte membrane while single-channel current decreased. From these data we conclude that cAMP triggered exocytotic delivery of preformed rENaCs to the plasma membrane. Ni(2+) (2.5 mM) inhibited about 60% of the rENaC current and conductance while C(m) remained unaffected. Noise analysis revealed that this inhibition could be attributed to a decrease in the apparent channel density, while single-channel current did not change significantly. These observations argue for direct effects of Ni(2+) on channel activity rather than induction of endocytotic removal of active channels from the plasma membrane.