TRPV6 mRNA Expression Research Articles

Effect of Tempeh and Daidzein on Calcium Status, Calcium Transporters, and Bone Metabolism Biomarkers in Ovariectomized Rats.

Menopause marks a critical life stage characterized by hormonal changes that significantly impact bone health, leading to a heightened susceptibility to bone fractures. This research seeks to elucidate the impact of daidzein and tempeh on calcium status, calcium transporters, and bone metabolism in an ovariectomized rat model. Forty female Wistar rats, aged 3 months, participated in a two-phase experiment. The initial phase involved inducing a calcium deficit, while the second phase comprised dietary interventions across five groups: Sham (S) and Ovariectomy (O) with a standard diet, O with bisphosphonate (OB), O with pure daidzein (OD), and O with tempeh (OT). Multiple parameters, encompassing calcium levels, calcium transporters, bone histopathology, and serum bone metabolism markers, were evaluated. The findings revealed that the OT group showcased heightened levels of bone turnover markers, such as pyridinoline, C-telopeptide of type I collagen, bone alkaline phosphatase, and procollagen type I N-terminal propeptide, in contrast to S and O groups, with statistical significance (p < 0.05). Histopathologically, both the OD and OT groups exhibited effects akin to the OB group, indicating a decrease in the surface area occupied by adipocytes in the femoral bone structure, although statistically non-equivalent, supporting the directionally similar trends. Although TRPV5 and TRPV6 mRNA expression levels in the jejunum and duodenum did not display statistically significant differences (p > 0.05), the OD and OT groups exhibited increased expression compared to the O group. We hypothesized that obtained results may be related to the effect of isoflavones on estrogen pathways because of their structurally similar to endogenous estrogen and weak estrogenic properties. In conclusion, the daily consumption of pure daidzein and tempeh could potentially improve and reinstate calcium status, calcium transport, and bone metabolism in ovariectomized rats. Additionally, isoflavone products demonstrate effects similar to bisphosphonate drugs on these parameters in ovariectomized rats.

High dietary Ca and microbial phytase reduce expression of Ca transporters while enhancing claudins involved in paracellular Ca absorption in the porcine jejunum and colon.

Expression levels of genes (RT-qPCR) related to Ca and P homeostasis (transporters and claudins (CLDN)) were determined in porcine jejunal and colonic mucosa. Forty growing pigs (BW 30.4±1.3 kg) received a low and high Ca content (2.0 and 9.6 g/kg, respectively) diet with or without microbial phytase (500 FTU/kg) for 21 days. Dietary Ca intake enhanced serum Ca and alkaline phosphatase concentration and reduced P, 1,25(OH)2D3, and parathyroid hormone concentration. Jejunal TRPV5 mRNA expression was decreased (32%) with phytase inclusion only, while colonic transient receptor potential vanilloid 5 (TRPV5) mRNA was reduced by dietary Ca (34%) and phytase (44%). Both jejunal and colonic TRPV6 mRNA expression was reduced (30%) with microbial phytase. Calbindin-D9k mRNA expression was lower in colonic but not jejunal mucosa with high dietary Ca (59%) and microbial phytase (37%). None of the mRNAs encoding the Na-P cotransporters (NaPi-IIc, PiT-1, PiT-2) were affected. Jejunal, but not colonic expression of the phosphate transporter XPR1, was slightly downregulated with dietary Ca. Dietary Ca downregulated colonic CLDN-4 (20%) and -10 (40%) expression while CLDN-7 was reduced by phytase inclusion in pigs fed low dietary Ca. Expression of colonic CLDN-12 tended to be increased by phytase. In jejunal mucosa, dietary Ca increased CLDN-2 expression (48%) and decreased CLDN-10 (49%) expression, while phytase slightly upregulated CLDN-12 expression. In conclusion, compared to a Ca deficient phytase-free diet, high dietary Ca and phytase intake in pigs downregulate jejunal and colonic genes related to transcellular Ca absorption and upregulate Ca pore-forming claudins.

Abstract 2891: Molecular profiling of hormone-resistant prostate cancer cells with TRPV6 oncochannel knockout/knockdown

Abstract TRPV6 calcium channel is a recognized oncochannel over-expressed in a number of epithelial cancers (e.g. breast, ovarian, prostate). TRPV6, a member of one of seven subfamilies of TRP channels, plays an important role in Ca2+ absorption from the intestinal lumen. TRPV6 over-expression is associated with a poor prognosis particularly with breast and prostate cancers. Although some TRPV6 mechanistic work is available and indicates that NFAT is involved, there is a need to better understand pathways involved in its mechanism of action (MOA). These data could allow the identification of clinically relevant biomarkers and identify potential for synergy of TRPV6-targeting therapies with other anti-cancer treatments. To determine which key pathways TRPV6 influences in prostate cancer, two TRPV6 knockouts (KO) were produced in a castration-resistant prostate cancer cell line (PC-3) using the CRISPR-Cas9 approach with two different gRNAs. In addition, knockdowns (KD) were produced by transfecting PC-3 cells with two TRPV6 siRNA targeting different regions of TRPV6 mRNA. The mRNA expression of 184 genes was analyzed using an RT-qPCR TaqMan array. The panel consisted of genes involved in cancer calcium signalling, genes that have been associated with the MOA of TRPV6 and genes directly or indirectly involved in NFAT signalling. Gene profiling results were generally consistent between the TRPV6 KD and KO cells. Results showed a dramatic reduction in expression of TRPV6 mRNA in the KO/KD cells (14 to 166-fold). TRPV6 KO/KD affected multiple genes involved in cancer cell proliferation (e.g. ESR1, CDH1), metastasis (e.g. SNAI1, MUC1/16), resistance to apoptosis (e.g. Bcl-2-type proteins, Fos) and angiogenesis (e.g. VEGFA/B, FLT4), as well as genes involved in the M2 immune tumor microenvironment (e.g. IL6 and VEGFA). The TRPV6 KO/KD data confirm the basic MOA of TRPV6, activating NFAT by increasing cytosolic calcium and provide information on the downstream pathways involved (e.g. NF-kB, estrogen and MAPK). The data allow for the identification of clinical efficacy biomarkers for TRPV6 inhibitors (e.g. a panel of CXCL12, FLT4, MUC16 and IL-6). Furthermore, results indicate TRPV6 inhibitors have the potential to modify the immune composition of the tumor microenvironment from a tumor promoting to a tumor control response, and thus may help trigger an anti-cancer immune defence. This study demonstrates a central role of TRPV6 and calcium signalling in cancer development. Citation Format: Tyler Lutes, Michelle Davey, Christopher Rice, Tyson MacCormack, John M. Stewart, Dominique Dugourd. Molecular profiling of hormone-resistant prostate cancer cells with TRPV6 oncochannel knockout/knockdown [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2891.

NCKX3 was compensated by calcium transporting genes and bone resorption in a NCKX3 KO mouse model

Gene knockout is the most powerful tool for determination of gene function or permanent modification of the phenotypic characteristics of an animal. Existing methods for gene disruption are limited by their efficiency, time required for completion and potential for confounding off-target effects. In this study, a rapid single-step approach to knockout of a targeted gene in mice using zinc-finger nucleases (ZFNs) was demonstrated for generation of mutant (knockout; KO) alleles. Specifically, ZFNs to target the sodium/calcium/potassium exchanger3 (NCKX3) gene in C57bl/6j were designed using the concept of this approach. NCKX3 KO mice were generated and the phenotypic characterization and molecular regulation of active calcium transporting genes was assessed when mice were fed different calcium diets during growth. General phenotypes such as body weight and plasma ion level showed no distinct abnormalities. Thus, the potassium/sodium/calcium exchanger of NCKX3 KO mice proceeded normally in this study. As a result, the compensatory molecular regulation of this mechanism was elucidated. Renal TRPV5 mRNA of NCKX3 KO mice increased in both male and female mice. Expression of TRPV6 mRNA was only down-regulated in the duodenum of male KO mice. Renal- and duodenal expression of PTHR and VDR were not changed; however, GR mRNA expression was increased in the kidney of NCKX3 KO mice. Depletion of the NCKX3 gene in a KO mouse model showed loss of bone mineral contents and increased plasma parathyroid hormone, suggesting that NCKX3 may play a role in regulating calcium homeostasis.

1α,25-Dihydroxyvitamin D3 enhances TRPV6 transcription through p38 MAPK activation and GADD45 expression

The active form of vitamin D, 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3], acts as a ligand for the vitamin D receptor (VDR), and regulates various physiological processes, including calcium and bone metabolism, cellular growth and differentiation, immunity and cardiovascular function. A number of vitamin D derivatives have been synthesized for the treatment of cancer and inflammatory disease, but the adverse effect of hypercalcemic activity due to intestinal calcium absorption has limited wide clinical application. The VDR target gene product TRPV6 is essential for intestinal calcium absorption. Our prior study has demonstrated that 1,25(OH)2D3 induces TRPV6 mRNA expression at lower concentrations than for induction of CYP24A1, a VDR target gene involved in vitamin D inactivation, in intestinal SW480 cells, suggesting an additional mechanism for vitamin D signaling on TRPV6 induction. By searching for a signal transduction pathway involved in 1,25(OH)2D3-induced expression of TRPV6, we found that a p38 mitogen-activated protein kinase (MAPK) inhibitor reduces the expression of TRPV6 but not CYP24A1 in 1,25(OH)2D3-treated SW480 cells. Knockdown experiments showed that p38α is involved in 1,25(OH)2D3-induced expression of TRPV6 but not CYP24A1. Treatment with a de novo protein synthesis inhibitor suppressed 1,25(OH)2D3-induced TRPV6 expression. Finally, we found that 1,25(OH)2D3 treatment induced expression of GADD45A, which encodes the GADD45α MAPK kinase kinase activator, earlier than TRPV6 expression and that GADD45A knockdown reduced TRPV6 induction by 1,25(OH)2D3. These findings indicate that p38α and GADD45α are involved in an enhanced vitamin D signaling on TRPV6 expression.

TRPV6 modulates proliferation of human pancreatic neuroendocrine BON-1 tumour cells.

Highly Ca2+ permeable receptor potential channel vanilloid type 6 (TRPV6) modulates a variety of biological functions including calcium-dependent cell growth and apoptosis. So far, the role of TRPV6 in controlling growth of pancreatic neuroendocrine tumour (NET) cells is unknown. In the present study, we characterize the expression of TRPV6 in pancreatic BON-1 and QGP-1 NET cells. Furthermore, we evaluate the impact of TRPV6 on intracellular calcium, the activity of nuclear factor of activated T-cells (NFAT) and proliferation of BON-1 cells. TRPV6 expression was assessed by real-time PCR and Western blot. TRPV6 mRNA expression and protein production were down-regulated by siRNA. Changes in intracellular calcium levels were detected by fluorescence calcium imaging (fura-2/AM). NFAT activity was studied by NFAT reporter assay; cell proliferation by bromodeoxyuridine (BrdU), MTT and propidium iodine staining. TRPV6 mRNA and protein are present in BON-1 and QGP-1 NET-cells. Down-regulation of TRPV6 attenuates BON-1 cell proliferation. TRPV6 down-regulation is associated with decreased Ca2+ response pattern and reduced NFAT activity. In conclusion, TRPV6 is expressed in pancreatic NETs and modulates cell proliferation via Ca2+-dependent mechanism, which is accompanied by NFAT activation.

Abstract LB-128: High prevalence of elevated TRPV6 mRNA in pancreatic ductal adenocarcinoma

Abstract SOR-C13, a 13-mer peptide derived from soricidin, the paralytic protein component of saliva of the Northern Short-tailed shrew, just completed an open-label, all comers phase I clinical trial for the treatment of epithelial-derived cancers. SOR-C13 is a first-in-class drug candidate that specifically targets and inhibits the TRPV6 calcium channel - a recognized oncochannel over-expressed in a number of epithelial cancers (e.g. breast, ovarian, prostate). TRPV6 over-expression is associated with a poor prognosis particularly with breast and prostate cancers. SOR-C13 is the first TRPV6-targeting drug to enter clinical development. Pancreatic patients were enrolled in the phase I clinical trial for SOR-C13 and for this reason the TRPV6 gene expression in pancreatic tumour biopsies was assessed. Association of TRPV6 oncochannel expression with aggressive pancreatic adenocarcinoma compared to neuroendocrine tumours has never been investigated. Pancreatic adenocarcinoma represents 90% of the pancreatic tumours and is associated with a poor prognosis compared to neuroendocrine tumours. TRPV6 gene expression was assessed in 19 pancreatic tumor biopsies including five adenocarcinoma (Grade I to III), one acinar cell (exocrine), and 13 neuroendocrine (Islet cell) tumors by two-step RT-qPCR. TRPV6 and β-actin (reference gene) mRNA expression was evaluated in duplicate in a reproducible TRPV6 plus β-actin duplex two-step RT-qPCR assay. The acinar cell, and 69% (9/13) of the neuroendocrine tumors had no detectable TRPV6 mRNA expression with &amp;gt;90% of neuroendocrine tumors (12/13) having very little TRPV6 mRNA expression (&amp;lt;30 copies/ng RNA). Of the five pancreatic adenocarcinoma biopsies 4/5 (80%) had 67-285 copies of TRPV6 mRNA/ng RNA, indicating a high level of TRPV6 expression in this type of aggressive pancreatic cancer. The β-actin CT was between 24 and 30 for all tumours (mean 28.5 ± 1.2) indicating that the lack TRPV6 amplification in a majority of the neuroendocrine tumors was not due to RT-qPCR failure or a lack of quality of the biopsy cDNA. Results indicate that drugs specifically targeting TRPV6 oncochannel, like SOR-C13, have the potential to be used to treat the high medical need in pancreatic ductal adenocarcinoma. Citation Format: Tyler Lutes, Dominique Dugourd, Michelle Davey, Christopher Rice, Stephanie St-Pierre, Jack M. Stewart. High prevalence of elevated TRPV6 mRNA in pancreatic ductal adenocarcinoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-128.

Lidocaine inhibits the invasion and migration of TRPV6-expressing cancer cells by TRPV6 downregulation.

It is well known that local anesthetics have a broad spectrum of pharmacological actions, acting as nerve blocks, and treating pain and cardiac arrhythmias via blocking of the sodium channel. The use of local anesthetics could reduce the possibility of cancer metastasis and recurrence following surgical tumor excision. The purpose of the present study was to investigate the inhibitory effect of lidocaine upon the invasion and migration of transient receptor potential cation channel subfamily V member 6 (TRPV6)-expressing cancer cells. Human breast cancer MDA-MB-231 cells, prostatic cancer PC-3 cells and ovarian cancer ES-2 cells were treated with lidocaine. Cell viability was quantitatively determined by MTT assay. The migration of the cells was evaluated using the wound healing assay, and the invasion of the cells was assessed using a Transwell assay. Calcium (Ca2+) measurements were performed using a Fluo-3 AM fluorescence kit. The expression of TRPV6 mRNA and protein in the cells was determined by quantitative-polymerase chain reaction and western blot analysis, respectively. The results suggested that lidocaine inhibits the cell invasion and migration of MDA-MB-231, PC-3 and ES-2 cells at lower than clinical concentrations. The inhibitory effect of lidocaine on TRPV6-expressing cancer cells was associated with a reduced rate of calcium influx, and could occur partly as a result of the downregulation of TRPV6 expression. The use of appropriate local anesthetics may confer potential benefits in clinical practice for the treatment of patients with TRPV6-expressing cancer.

Polymodal Transient Receptor Potential Vanilloid (TRPV) Ion Channels in Chondrogenic Cells.

Mature and developing chondrocytes exist in a microenvironment where mechanical load, changes of temperature, osmolarity and acidic pH may influence cellular metabolism. Polymodal Transient Receptor Potential Vanilloid (TRPV) receptors are environmental sensors mediating responses through activation of linked intracellular signalling pathways. In chondrogenic high density cultures established from limb buds of chicken and mouse embryos, we identified TRPV1, TRPV2, TRPV3, TRPV4 and TRPV6 mRNA expression with RT-PCR. In both cultures, a switch in the expression pattern of TRPVs was observed during cartilage formation. The inhibition of TRPVs with the non-selective calcium channel blocker ruthenium red diminished chondrogenesis and caused significant inhibition of proliferation. Incubating cell cultures at 41 °C elevated the expression of TRPV1, and increased cartilage matrix production. When chondrogenic cells were exposed to mechanical load at the time of their differentiation into matrix producing chondrocytes, we detected increased mRNA levels of TRPV3. Our results demonstrate that developing chondrocytes express a full palette of TRPV channels and the switch in the expression pattern suggests differentiation stage-dependent roles of TRPVs during cartilage formation. As TRPV1 and TRPV3 expression was altered by thermal and mechanical stimuli, respectively, these are candidate channels that contribute to the transduction of environmental stimuli in chondrogenic cells.

Comparative effects of 1α‐hydroxyvitamin D3 and 1,25‐dihydroxyvitamin D3 on transporters and enzymes in fxr(+/+) and fxr(‐/‐) mice

Previous studies have shown that 1α,25-dihydroxyvitamin D3 [1,25(OH)2 D3 ] treatment in mice resulted in induction of intestinal and renal Cyp24a1 and Trpv6 expression, increased hepatic Cyp7a1 expression and activity, as well as higher renal Mdr1/P-gp expression. The present study compared the equimolar efficacies of 1α-hydroxyvitamin D3 [1α(OH)D3 ] (6 nmol/kg i.p. q2d × 4), a lipophilic precursor with a longer plasma half-life that is converted to 1,25(OH)2 D3 , and 1,25(OH)2 D3 on vitamin D receptor (VDR) target genes. To clarify whether changes in VDR genes was due to VDR and not secondary, farnesoid X receptor (FXR)-directed effects, namely, lower Cyp7a1 expression in rat liver due to increased bile acid absorption, wildtype [fxr(+/+)] and FXR knockout [fxr(-/-)] mice were used to distinguish between VDR and FXR effects. With the exception that hepatic Sult2a1 mRNA was increased equally well by 1α(OH)D3 and 1,25(OH)2 D3 , 1α(OH)D3 treatment led to higher increases in hepatic Cyp7a1, renal Cyp24a1, VDR, Mdr1 and Mrp4, and intestinal Cyp24a1 and Trpv6 mRNA expression in both fxr(+/+) and fxr(-/-) mice compared to 1,25(OH)2 D3 treatment. A similar induction in protein expression and microsomal activity of hepatic Cyp7a1 and renal P-gp and Mrp4 protein expression was noted for both compounds. A higher intestinal induction of Trpv6 was observed, resulting in greater hypercalcemic effect following 1α(OH)D3 treatment. The higher activity of 1α(OH)D3 was explained by its rapid conversion to 1,25(OH)2 D3 in tissue sites, furnishing higher plasma and tissue 1,25(OH)2 D3 levels compared to following 1,25(OH)2 D3 -treatment. In conclusion, 1α(OH)D3 exerts a greater effect on VDR gene induction than equimolar doses of 1,25(OH)2 D3 in mice.

Sulforaphane and trichostatin A histone deacetylase inhibitors increase vitamin D‐induced CYP24 expression in intestinal cells

Epigenetic changes, such as acetylation of nuclear histone proteins, can be induced by bioactive food components and alter chromatin structure and the expression of certain genes. Sulforaphane (SFN) and trichostatin A (TSA) have histone deacetylase inhibitor (HDACI) activity. We hypothesized that HDACI treatment would increase vitamin D‐induced CYP24 and TRPV6 gene expression. We tested the effect of four dosages of SFN (1, 2.5, 5 and 10 μmol/L) and one dose of TSA (1 μmol/L) with and without the presence of 10 nmol/L 1, 25‐dihydroxyvitamin D (1, 25 (OH)2D) for 24h on the expression of CYP24 and TRPV6 in the Caco‐2 human intestinal cell model. Western blot analysis showed an increase in the protein expression levels of CYP24 with SFN and 1,25 (OH)2D. Realtime qPCR was used to calculate the relative change in mRNA expression of CYP24 and TRPV6. TSA alone increased (p&lt;.05) CYP24 mRNA expression. 1,25 (OH)2D increased CYP24 and TRPV6 mRNA expression in Caco‐2 cells. TSA also increased vitamin D‐induced CYP24 mRNA expression, but vitamin D‐induced TRPV6 expression was not affected by HDACI treatment. Our results demonstrate that HDACIs can differentially affect the expression of certain vitamin D‐dependent genes in Caco‐2 intestinal cells. Additional studies are needed to determine HDACI effects on vitamin D‐related functions in vivo. This work was supported by a Massachusetts Experiment Station HATCH grant MAS000902

Evaluation of a possible direct effect by casein phosphopeptides on paracellular and vitamin D controlled transcellular calcium transport mechanisms in intestinal human HT-29 and Caco2 cell lines

Intestinal cells are continuously exposed to food whose components are able to modulate some of their physiological functions. Among the bioactive food derivatives are casein phosphopeptides (CPPs), coming from the in vitro or in vivo casein digestion, which display the ability to form aggregates with calcium ions and to increase the uptake of the minerals in differentiated intestinal human HT-29 and Caco2 cells. Since extracellular calcium is a known inactivator of the TRPV6 channel, which is also involved in the colon cancer progression, the present study aims to determine a possible modulation by CPPs of the molecular structures responsible for paracellular and/or transcellular calcium absorption in these two cell lines. The paracellular calcium transport was determined by TEER measurements in Caco2 cells and by Lucifer Yellow flow in HT-29 cells. The possible modulation of transcellular calcium absorption machinery by CPPs was investigated by determining the mRNA expression for both the TRPV6 calcium channel and the VDR receptor in 1,25(OH)₂D₃ pre-treated undifferentiated/differentiated cells. The results obtained point out that: (i) CPPs do not affect paracellular calcium absorption; (ii) 1,25(OH)₂D₃ increases the TRPV6 mRNA expression in both types of cells. In the case of HT-29 cells this is the first determination of the presence of the TRPV6 channel; (iii) CPPs per se are not able to affect the VDR and TRPV6 mRNA expression; (iv) CPP administration does not affect the TRPV6 mRNA expression in 1,25(OH)₂D₃ pre-treated HT-29 cells and Caco2 cells. Unlike peptides coming from the digestion of cheese whey protein digest, the digestion of milk casein produces peptides with no effects on TRPV6 calcium channel expression, though the same peptides are able to determine a calcium uptake by the intestinal cells.

Calcium Ion Transport-Related Genes, TRPV6, PMCA1, NCKX3, CaBP-28k Are Differentially Expressed in Human Placental Cell Line (BeWo).

Preeclampsia is pregnancy-specific disease characterized de-novo development of concurrent hypertension, proteinuria and oxidative stress in placenta. Hypoxia occurs during the development of placenta in the first trimester and is implicated in trophoblast differentiation. In placenta, intervillous blood flow increases after 10 weeks of gestation and results in exposure of trophoblast cells to oxygen. During last trimester of gestation, the calcium (Ca2+) transport from mother to fetus increases dramatically in response to the accelerated demand for Ca2+ caused by bone mineralization in the fetus. Regarding the molecular basis of Ca2+ transport, several studies suggest that transcellular active Ca2+ transport is comprised of three processes: (1) the apical Ca2+ entry, (2) the binding with calbindins that serves as an intracellular Ca2+ buffer, and (3) basolateral exit. In this study, cell membrane and cytosolic calcium transporters (TRPV6, PMCA1, NCKX3 and CaBP-28k) were investigated at induced oxidative stress in human placental cell line (BeWo). The expression of calcium transporters (TRPV6, PMCA1, NCKX3 and CaBP-28k) were potential roles in BeWo cell remain to be clarified. In hypoxia, human placental cell (BeWo) expression of TRPV6 mRNA and protein level was not altered, however, calcium transporters (NCKX3, CaBP-28k) were increase at hypoxic BeWo cell compared with control group (normoxia). In addition, expression of PMCA1 mRNA and protein was decreased at hypoxic BeWo cell. Taken together, these results indicate that calcium transporters (TRPV6, PMCA1, NCKX3 and CaBP-28k) are distinctly expressed by induced oxidative stress, in BeWo cell, suggesting that alterations of calcium transporters in hypoxic stress may be involved in placenta cell is a determinant factor affecting calcium transfer in BeWo cell model. (poster)

Down-regulation of Intestinal Apical Calcium Entry Channel TRPV6 by Ubiquitin E3 Ligase Nedd4-2

Nedd4-2 is an archetypal HECT ubiquitin E3 ligase that disposes target proteins for degradation. Because of the proven roles of Nedd4-2 in degradation of membrane proteins, such as epithelial Na(+) channel, we examined the effect of Nedd4-2 on the apical Ca(2+) channel TRPV6, which is involved in transcellular Ca(2+) transport in the intestine using the Xenopus laevis oocyte system. We demonstrated that a significant amount of Nedd4-2 protein was distributed to the absorptive epithelial cells in ileum, cecum, and colon along with TRPV6. When co-expressed in oocytes, Nedd4-2 and, to a lesser extent, Nedd4 down-regulated the protein abundance and Ca(2+) influx of TRPV6 and TRPV5, respectively. TRPV6 ubiquitination was increased, and its stability was decreased by Nedd4-2. The Nedd4-2 inhibitory effects on TRPV6 were partially blocked by proteasome inhibitor MG132 but not by the lysosome inhibitor chloroquine. The rate of TRPV6 internalization was not significantly altered by Nedd4-2. The HECT domain was essential to the inhibitory effect of Nedd4-2 on TRPV6 and to their association. The WW1 and WW2 domains interacted with TRPV6 terminal regions, and a disruption of the interactions by D204H and D376H mutations in the WW1 and WW2 domains increased TRPV6 ubiquitination and degradation. Thus, WW1 and WW2 may serve as a molecular switch to limit the ubiquitination of TRPV6 by the HECT domain. In conclusion, Nedd4-2 may regulate TRPV6 protein abundance in intestinal epithelia by controlling TRPV6 ubiquitination.

186 DUODENAL AND RENAL TRANSIENT RECEPTOR POTENTIAL VANILLOID 6 APPEAR TO BE DISTINCTLY REGULATED BY SEX STEROID HORMONES, ESTROGEN AND PROGESTERONE, IN IMMATURE FEMALE RATS

Calcium-related proteins include transient receptor potential vanilloid (TRPV) 5 and 6, plasma membrane calcium-ATPase 1b (PMCA1b), and calbindin-D9k and -D28k. The TRPV6 is a major calcium channel located in the apical and basolateral membranes of cell and distributed widely in many other organs, especially in the exocrine tissues such as intestine and uterus. TRPV6s are generally regulated by vitamin D, a dietary calcium ion and hormone. In particular, uterine TRPV6 appears to be affected by sex steroid hormones, which are altered according to estrous cycle and pregnancy. In order to discover the effect of sex steroid hormones on the regulation of TRPV6, we examined the expression of TRPV6 mRNA by using RT-PCR and real-time PCR, and protein expression of TRPV6 by immunohistochemistry (IHC) in the uterus, duodenum, and kidney. To evaluate the effect(s) of sex steroid hormones on its uterine, duodenal, and renal regulation, 17β-estradiol [E2; 40 μg kg–1 of body weight (bw)] and/or progesterone (P4; 4 mg kg–1 of bw) or vehicle (n = 6/each group) were subcutaneously injected into Sprague-Dawley immature female rats (14 days old, n = 24 in total) for 3 days. As a result, the treatments of immature rats with E2 or P4 increased TRPV6 mRNA for calcium function or regulation in the uterus of immature rats. To confirm the specificity of E2 or P4 through their receptors, we treated the immature rats (extra n = 24 in total) with an estrogen receptor-antagonist, ICI 182,780 (ICI; 30 μg kg–1 of bw), and/or progesterone receptor antagonist, RU 486 (10 mg kg–1 of bw), at 3 days prior to E2 or P4 injection. Consequently, an increase in TRPV6 mRNA was observed in the following 2 treatments; ICI plus E2/P4 and E2/P4 alone. In IHC, we further observed that the expression of duodenal TRPV6 was increased by E2 or P4 and E2 or P4 plus ICI, while no difference was observed in renal TRPV6 by the treatments of sex steroid hormones. In conclusion, these results indicate that the expressions of uterine and duodenal TRPV6 may be induced by E2 and P4, but its renal expression may not be controlled by these steroids.

The role of TRPV6 in breast carcinogenesis

TRPV6 is an endothelial calcium entry channel that is strongly expressed in breast adenocarcinoma tissue. In this study, we further confirmed this observation by analysis of breast cancer tissues, which indicated that TRPV6 mRNA expression was up-regulated between 2-fold and 15-fold compared with the average in normal breast tissue. Whereas TRPV6 is expressed in the cancer tissue, its role as a calcium channel in breast carcinogenesis is poorly understood. Therefore, we investigated how TRPV6 affects the viability, apoptosis, and calcium transport in the breast cancer cell line T47D. Hormones can also affect the tumor development; hence, we determined the effects of estradiol, progesterone, and 1,25-vitamin D on TRPV6 transcription. Interestingly, the estrogen receptor antagonist tamoxifen reduced expression of TRPV6 and is able to inhibit its calcium transport activity (IC(50), 7.5 micromol/L). The in vitro model showed that TRPV6 can be regulated by estrogen, progesterone, tamoxifen, and 1,25-vitamin D and has a large influence on breast cancer cell proliferation. Moreover, the effect of tamoxifen on cell viability was enhanced when TRPV6 expression was silenced with small interfering RNA. TRPV6 may be a novel target for the development of calcium channel inhibitors to treat breast adenocarcinoma expressing TRPV6.

TRPV6 Is a Ca2+ Entry Channel Essential for Ca2+-induced Differentiation of Human Keratinocytes

Ca(2+) is an essential factor inducing keratinocyte differentiation due to the natural Ca(2+) gradient in the skin. However, the membrane mechanisms that mediate calcium entry and trigger keratinocyte differentiation had not previously been elucidated. In this study we demonstrate that Ca(2+)-induced differentiation up-regulates both mRNA and protein expression of a transient receptor potential highly Ca(2+)-selective channel, TRPV6. The latter mediates Ca(2+) uptake and accounts for the basal [Ca(2+)](i) in human keratinocytes. Our results show that TRPV6 is a prerequisite for keratinocyte entry into differentiation, because the silencing of TRPV6 in human primary keratinocytes led to the development of impaired differentiated phenotype triggered by Ca(2+). The expression of such differentiation markers as involucrin, transglutaminase-1, and cytokeratin-10 was significantly inhibited by small interfering RNA-TRPV6 as compared with differentiated control cells. TRPV6 silencing affected cell morphology and the development of intercellular contacts, as well as the ability of cells to stratify. 1,25-Dihydroxyvitamin D3, a cofactor of differentiation, dose-dependently increased TRPV6 mRNA and protein expression in human keratinocytes. This TRPV6 up-regulation led to a significant increase in Ca(2+) uptake in both undifferentiated and differentiated keratinocytes. We conclude that TRPV6 mediates, at least in part, the pro-differentiating effects of 1,25-dihydroxyvitamin D3 by increasing Ca(2+) entry, thereby promoting differentiation. Taken together, these data suggest that the TRPV6 channel is a key element in Ca(2+)/1,25-dihydroxyvitamin D3-induced differentiation of human keratinocytes.

Uterine TRPV6 expression during the estrous cycle and pregnancy in a mouse model

Maintenance of uterine calcium balance is crucial for physiological functioning, including smooth muscle contraction and embryo implantation. Although calbindins were previously thought to act as important uterine calcium-processing genes for female reproductive function, they were not enough to attest the roles of calcium ions in the reproductive organs. Previously, we reported that rat transient receptor potential cation channel, subfamily V, member 6 (TRPV6) was expressed and regulated by hormones in the uterus. In the present study, we observed uterine TRPV6 expression in a mouse model to clarify the mutual roles of these two calcium-processing genes in female reproductive organs. We investigated uterine TRPV6 mRNA expression during the estrous cycle and pregnancy, as well as its regulation by the steroid hormones estrogen (E2) and progesterone (P4) in mice. Uterine TRPV6 mRNA levels increased at estrus and fluctuated in the uterus, placenta, and fetal membrane during pregnancy. Uterine TRPV6 mRNA increased in mid- and late pregnancy, and its expression was strongly induced in midpregnancy in the labyrinth and spongy zones of the placenta, and in the fetal membrane. E2 (17beta-estradiol) was found to regulate uterine TRPV6 expression in the luminal and glandular epitheliums. In addition, we determined that ERalpha tightly regulated uterine TRPV6 transcription. Together, these results suggest that for uterine function in normal pregnancy, TRPV6 is regulated by E2 via an ERalpha-dependent pathway.

Differential effects of Vitamin D analogs on calcium transport

It is well known that the efficiency of intestinal active calcium transport is regulated by the Vitamin D receptor pathway and Vitamin D analogs seem to exhibit differential effects on intestinal active calcium transport. To investigate the molecular basis for the difference among Vitamin D analogs, we tested three Vitamin D analogs: 1,25-dihydroxyvitamin D 3, 19-nor-1,25-dihydroxyvitamin D 2, and 1α-hydroxyvitamin D 2 ex vivo and in vitro. In 5/6 nephrectomized rat intestinal active calcium transport, 19-nor-1,25-dihydroxyvitamin D 2 did not show a significant effects on intestinal active calcium transport at all the concentrations tested, while 1α-hydroxyvitamin D 2 at 0.33 and 0.67 μg/kg and 1,25-dihydroxyvitamin D 3 at 1 μg/kg significantly stimulated calcium transport. In Caco-2 cells, 19-nor-1,25-dihydroxyvitamin D 2 did not show a significant effect on calcium transport, while 1,25-dihydroxyvitamin D 3 and 1,25-dihydroxyvitamin D 2 (the active form of 1α-hydroxyvitamin D 2) stimulated calcium transport by 934 and 501% at 0.1 μM, respectively. 1,25-Dihydroxyvitamin D 2 potently induced the expression of CALB3 and TRPV6 mRNA with an EC 50 of 0.3 and 1.0 nM, whereas 19-nor-1,25-dihydroxyvitamin D 2 was 10-fold less potent than 1,25-dihydroxyvitamin D 2 in inducing CALB3 and TRPV6 mRNA. The three Vitamin D analogs had no significant effect on the expression of PMCA1 mRNA. These Vitamin D analogs did not change the expression of Vitamin D receptor (VDR) up to 10 nM, but stimulated CYP24A1 expression in a dose-dependent manner with the potency in the order of 1,25-dihydroxyvitamin D 3 > 1,25-dihydroxyvitamin D 2 = 19-nor-1,25-dihydroxyvitamin D 2. These results suggest that the differential effect of Vitamin D analogs on stimulating intestinal and Caco-2 calcium transport may be in part due to its different effect on stimulating CALB3 and TRPV6 mRNA expression.

1,25–Dihydroxyvitamin D and 25–hydroxyvitamin D—mediated regulation of TRPV6 (a putative epithelial calcium channel) mRNA expression in Caco–2 cells

TRPV6 is a member of the vanilloid subfamily of transient receptor potential (TRP) proteins and likely functions as an epithelial calcium channel in calcium-transporting organs, such as the intestine, kidney, and placenta. TRPV6 mRNA expression is strongly regulated by 1,25-dihydroxyvitamin D (1,25VD), the active hormonal form of vitamin D, in intestine and in Caco-2 cells, a human colon cancer cell line. The aim of the present study was to characterise the mode of regulation of the 1,25VD-mediated TRPV6 mRNA expression and to test the effect of the precursor of 1,25VD namely 25 hydroxyvitamin D (25 VD) on TRPV6 mRNA expression in Caco-2 cells. Caco-2 cells were treated in a 2 x 2 format with 1,25VD and the transcriptional inhibitor actinomycin D (AD, 4 microg/ml), and also with translational inhibitor cycloheximide (CHX, 10 microg/ml) after 14 days in culture and TRPV6 mRNA levels were determined using reverse transcription-real time PCR.TRPV6 mRNA half life studies were performed by inhibiting transcription followed by sampling at various time points for TRPV6 mRNA. Varying concentrations of 25 VD were used to test their effect on TRPV6 mRNA in the presence of 5% FBS and also in the absence of serum (but containing insulin-transferrin-selenium mixture) for 24 h. Treatment with 10(-7) M 1,25VD for 8 h resulted in a 60-fold increase in TRPV6 mRNA and this increase could be completely blocked with AD. Treatment with CHX to inhibit de novo protein synthesis did not prevent the initiation of 1,25VD-induced TRPV6 expression, although it did reduce the extent of TRPV6 mRNA accumulation. We found that TRPV6 mRNA half-life was 8 h in Caco-2 cells and was not altered by 1,25VD treatment. Finally, we observed that treatment with 10(-6) M of the pro-hormone 25 VD for 24 h resulted in a significant increase in TRPV6 expression in Caco-2 cells, which is consistent with the presence of 1alpha-hydroxylase (CYP27B1) expression in Caco-2 cells and a possible autocrine vitamin D signaling pathway in colon cells. 1,25 dihydroxyvitamin D regulates TRPV6 expression by a process that requires new mRNA and protein synthesis and the point of regulation lies likely at the transcriptional level especially since vitamin D did not increase the half life of TRPV6 mRNA. In addition, the prohormone form of 1,25 dihydroxyvitamin D, i. e. the 25 hydroxyvitamin D, induced TRPV6 mRNA expression in Caco-2 cells.