Calcyclin is an early vasopressin-induced gene in the renal collecting duct. Role in the long term regulation of ion transport

S100A6 Protein-Expression and Function in Norm and Pathology

S100A6, also known as calcyclin, is a calcium-binding protein belonging to the S100 protein family. It was first identified and purified more than 30 years ago. Initial structural studies, focused mostly on the mode and affinity of Ca²⁺ binding and resolution of the resultant conformational changes, were soon complemented by research on its expression, localization and identification of binding partners. With time, the use of biophysical methods helped to resolve the structure and versatility of S100A6 complexes with some of its ligands. Meanwhile, it became clear that S100A6 expression was altered in various pathological states and correlated with the stage/progression of many diseases, including cancers, indicative of its important, and possibly causative, role in some of these diseases. This, in turn, prompted researchers to look for the mechanism of S100A6 action and to identify the intermediary signaling pathways and effectors. After all these years, our knowledge on various aspects of S100A6 biology is robust but still incomplete. The list of S100A6 ligands is growing all the time, as is our understanding of the physiological importance of these interactions. The present review summarizes available data concerning S100A6 expression/localization, interaction with intracellular and extracellular targets, involvement in Ca²⁺-dependent cellular processes and association with various pathologies.

S100A6 is a positive regulator of PPP5C-FKBP51-dependent regulation of endothelial calcium signaling

I_SOC is a cation current permeating the ISOC channel. In pulmonary endothelial cells, I_SOC activation leads to formation of inter-endothelial cell gaps and barrier disruption. The immunophilin FK506-binding protein 51 (FKBP51), in conjunction with the serine/threonine protein phosphatase 5C (PPP5C), inhibits I_SOC . Free PPP5C assumes an autoinhibitory state, which has low "basal" catalytic activity. Several S100 protein family members bind PPP5C increasing PPP5C catalytic activity in vitro. One of these family members, S100A6, exhibits a calcium-dependent translocation to the plasma membrane. The goal of this study was to determine whether S100A6 activates PPP5C in pulmonary endothelial cells and contributes to I_SOC inhibition by the PPP5C-FKBP51 axis. We observed that S100A6 activates PPP5C to dephosphorylate tau T231. Following I_SOC activation, cytosolic S100A6 translocates to the plasma membrane and interacts with the TRPC4 subunit of the ISOC channel. Global calcium entry and I_SOC are decreased by S100A6 in a PPP5C-dependent manner and by FKBP51 in a S100A6-dependent manner. Further, calcium entry-induced endothelial barrier disruption is decreased by S100A6 dependent upon PPP5C, and by FKBP51 dependent upon S100A6. Overall, these data reveal that S100A6 plays a key role in the PPP5C-FKBP51 axis to inhibit I_SOC and protect the endothelial barrier against calcium entry-induced disruption.

Glial S100A6 Degrades β-amyloid Aggregation through Targeting Competition with Zinc Ions

Evidence has been accumulating that zinc ions can trigger β-amyloid (Aβ) deposition and senile plaque formation in the brain, a pathological hallmark of Alzheimer's disease (AD). Chelating zinc inhibits Aβ aggregation and may hold promise as a therapeutic strategy for AD. S100A6 is an acidic Ca²⁺/Zn²⁺-binding protein found only in a small number of astrocytes in the normal brain. However, in the AD brain, S100A6 is highly expressed in astrocytes around Aβ plaques. The role of the astrocytic S100A6 upregulation in AD is unknown. In the present study, we examined the effects of S100A6 on Aβ plaques and intracellular zinc levels in a mouse model of AD. Chronic exposure to zinc increased Aβ deposition and S100A6 expression, both reversible by the zinc chelator clioquinol, in the brains of amyloid precursor protein/presenilin 1 (APP/PS1) transgenic mice. To examine whether exogenous S100A6 could induce Aβ plaque disaggregation through competition for zinc in vitro, we incubated APP/PS1 mouse brain sections with recombinant human S100A6 protein or co-incubated them with human S100A6-expressing cells. Both treatments efficiently reduced the Aβ plaque burden in situ. In addition, treatment with exogenous S100A6 protected cultured COS-7 cells against zinc toxicity. Our results show for the first time that increased S100A6 levels correlate with both Aβ disaggregation and decrease of Aβ plaque-associated zinc contents in brain sections with AD-like pathology. Astrocytic S100A6 in AD may protect from Aβ deposition through zinc sequestration.

S100A6 promotes proliferation of intrahepatic cholangiocarcinoma cells via the activation of the p38/MAPK pathway

Aim: We explored the expression of S100A6 and its role in intrahepatic cholangiocarcinoma (ICC). Methods: The expression of S100A6 in ICC samples was detected by immunohistochemistry. In vitro experiments, we silenced and overexpressed S100A6 to investigate its role in cell functions. Results: The expression of S100A6 was markedly increased in ICC tissues and cell lines. S100A6 overexpression was an independent risk factor for patients’ survival. Silencing S100A6 resulted in a suppression of proliferation and p38/MAPK activity, while overexpressing S100A6 caused a promotion of proliferation and p38/MAPK. Discussion: S100A6 participated in the proliferation of ICC cells and correlated with a more aggressive behavior of ICC. Conclusion: S100A6 may serve as a novel prognostic marker and a potential therapeutic target for ICC patients.

S100A6 protein: functional roles

S100A6 protein belongs to the A group of the S100 protein family of Ca2+-binding proteins. It is expressed in a limited number of cell types in adult normal tissues and in several tumor cell types. As an intracellular protein, S100A6 has been implicated in the regulation of several cellular functions, such as proliferation, apoptosis, the cytoskeleton dynamics, and the cellular response to different stress factors. S100A6 can be secreted/released by certain cell types which points to extracellular effects of the protein. RAGE (receptor for advanced glycation endproducts) and integrin β1 transduce some extracellular S100A6's effects. Dosage of serum S100A6 might aid in diagnosis in oncology.

S100A6 promotes cell proliferation in human nasopharyngeal carcinoma via the p38/MAPK signaling pathway

An elevated level of S100A6 is associated with poor outcomes of many tumor types, but, how S100A6 contributes to nasopharyngeal carcinoma (NPC) progression remains unknown. Here, we investigated the expression and prognostic significance of S100A6 in NPC and explored the molecular mechanisms under-lying the role of S100A6 in NPC development. The results showed that S100A6 was markedly up-regulated in NPC tissues and cell lines compared to paired peritumoral normal tissues and a normal nasopharyngeal epithelial cell line, respectively. In tissues from 92 NPC patients, high S100A6 expression was associated with advanced N stage, locoregional failure and disease progression and was predictive of poor locoregional recurrence-free survival (LRRFS, P = 0.001) and progression-free survival (PFS, P = 0.001). Multivariate analysis showed that S100A6 is an independent prognostic factor for LRRFS and PFS. Silencing S100A6 using siRNA or shRNA significantly suppressed NPC cell proliferation, colony formation and p38/mitogen-activated protein kinase (MAPK) activity in vitro and inhibited tumor growth in a xenograft mouse model of NPC. In contrast, overexpressing S100A6 via plasmid transfection resulted in increased NPC cell proliferation and p38/MAPK activation. S100A6-induced proliferation was abolished by a p38 inhibitor. In summary, S100A6 may be a new prognostic marker of NPC and may promote NPC development via the activation of p38/MAPK signaling pathways. These findings suggest S100A6/p38/MAPK signaling as a potential therapeutic target for NPC. © 2016 Wiley Periodicals, Inc.

High-level S100A6 promotes metastasis and predicts the outcome of T1-T2 stage in clear cell renal cell carcinoma

S100A6 (calcyclin), functions in cell cycle progression and differentiation, has been reported to promote the tumorigenesis and malignancy of many types of cancers. Clear cell renal cell carcinoma (ccRCC) is the most common subtype of RCC, lacking both promising prognostic markers and effective therapeutic targets. In our previous study, we have found the elevated S100A6 in the ccRCC tumor tissues, and the differentially expressed genes determined by microarray analysis were found to be strongly related to tumor metastasis after S100A6 knockdown and overexpression in the ccRCC cell line 786-O. The mRNA expression of S100A6 detected by RT-PCR in 6 cell lines and 174 tumor tissues, including 58 metastatic ccRCC and 116 clinicopathological features paired non-metastatic ccRCC (1:2), indicated S100A6 was elevated in the metastatic cells and tumor tissues. The protein expression was consistent with mRNA expression. The biological function of S100A6 in promoting metastasis was determined through overexpression and knockdown of S100A6 in the ccRCC cell lines 786-O, caki-1, and ACHN. In the scratch wound migration assay as well as migration and invasion assays, S100A6 knockdown significantly suppressed the migratory and invasive abilities of tumor cells, whereas overexpression enhanced the malignancy. Further research with the follow-up data of 129 ccRCC patients were analyzed by the Cox regression and survival analysis. The expression of S100A6 was up-regulated in metastatic ccRCC cells. In the metastatic tumor tissues, the expression of S100A6 was also higher than in the non-metastatic tissues. High S100A6 expression might be crucial to promote metastasis in ccRCC by enhancing the ability of tumor cells migration and invasion. In addition, the quantitative mRNA expression of S100A6 in the tumor tissues was an independent risk factor and might be used as a prognostic marker for the metastatic risk of the localized T1-T2 stage ccRCC.

Expression of S100A6 in rat hippocampus after traumatic brain injury due to lateral head acceleration

In a rat model of traumatic brain injury (TBI), we investigated changes in cognitive function and S100A6 expression in the hippocampus. TBI-associated changes in this protein have not previously been reported. Rat S100A6 was studied via immunohistochemical staining, Western blot, and reverse transcription-polymerase chain reaction (RT-PCR) after either lateral head acceleration or sham. Reduced levels of S100A6 protein and mRNA were observed 1 h after TBI, followed by gradual increases over 6, 12, 24, and 72 h, and then a return to sham level at 14 day. Morris water maze (MWM) test was used to evaluate animal spatial cognition. TBI- and sham-rats showed an apparent learning curve, expressed as escape latency. Although TBI-rats displayed a relatively poorer cognitive ability than sham-rats, the disparity was not significant early post-injury. Marked cognitive deficits in TBI-rats were observed at 72 h post-injury compared with sham animals. TBI-rats showed decreased times in platform crossing in the daily MWM test; the performance at 72 h post-injury was the worst. In conclusion, a reduction in S100A6 may be one of the early events that lead to secondary cognitive decline after TBI, and its subsequent elevation is tightly linked with cognitive improvement. S100A6 may play important roles in neuronal degeneration and regeneration in TBI.

Differentially expressed genes of human microvascular endothelial cells in response to anti-dengue virus NS1 antibodies by suppression subtractive hybridization

It has been previously shown that anti-dengue virus (DENV) nonstructural protein NS1 antibodies could act as autoantibodies that direct against one or more of the host's own proteins, which has potential implications for dengue hemorrhagic fever pathogenesis. In the present study, we have employed suppression subtractive hybridization (SSH) to identify the differentially expressed genes from human microvascular endothelial cells (HMEC-1) in response to anti-dengue virus type 2 NS1 antibodies (anti-DENV2 NS1 Abs). A total of 35 clones from the SSH cDNA library were randomly selected for further analysis using bioinformatics tools after vector screening. After searching for sequence homology in NCBI GenBank database with BLASTN and BLASTX programs, 23 obtained sequences with significant matches (E-values <1×10(-4)) in the SSH library. The predicted genes in the subtracted library include immune response molecules (CD59 antigen preproprotein preproprotein, MURR1), signal transduction molecules (Nuclear casein kinase and cyclin-dependent kinase substrate 1), calcium-binding proteins (S100A6, Annexin A2 isoform 1/2), and cell-membrane component (Yip1 domain family). From these clones, 5 upregulated genes were selected for differential expression profiling by real-time RT-PCR to confirm their upregulated status. The results confirmed their differential upregulation, and thus verified the success of SSHs and the likely involvement of these genes in dengue pathogenesis.

Quantitative phosphoproteomics in nuclei of vasopressin-sensitive renal collecting duct cells

Vasopressin regulates transport across the collecting duct epithelium in part via effects on gene transcription. Transcriptional regulation occurs partially via changes in phosphorylation of transcription factors, transcriptional coactivators, and protein kinases in the nucleus. To test whether vasopressin alters the nuclear phosphoproteome of vasopressin-sensitive cultured mouse mpkCCD cells, we used stable isotope labeling and mass spectrometry to quantify thousands of phosphorylation sites in nuclear extracts and nuclear pellet fractions. Measurements were made in the presence and absence of the vasopressin analog dDAVP. Of the 1,251 sites quantified, 39 changed significantly in response to dDAVP. Network analysis of the regulated proteins revealed two major clusters ("cell-cell adhesion" and "transcriptional regulation") that were connected to known elements of the vasopressin signaling pathway. The hub proteins for these two clusters were the transcriptional coactivator β-catenin and the transcription factor c-Jun. Phosphorylation of β-catenin at Ser552 was increased by dDAVP [log(2)(dDAVP/vehicle) = 1.79], and phosphorylation of c-Jun at Ser73 was decreased [log(2)(dDAVP/vehicle) = -0.53]. The β-catenin site is known to be targeted by either protein kinase A or Akt, both of which are activated in response to vasopressin. The c-Jun site is a canonical target for the MAP kinase Jnk2, which is downregulated in response to vasopressin in the collecting duct. The data support the idea that vasopressin-mediated control of transcription in collecting duct cells involves selective changes in the nuclear phosphoproteome. All data are available to users at http://helixweb.nih.gov/ESBL/Database/mNPPD/.

S100A6 (calcyclin) deficiency induces senescence-like changes in cell cycle, morphology and functional characteristics of mouse NIH 3T3 fibroblasts

S100A6 (calcyclin) is a calcium binding protein with two EF-hand structures expressed mostly in fibroblasts and epithelial cells. We have established a NIH 3T3 fibroblast cell line stably transfected with siRNA against S100A6 to examine the effect of S100A6 deficiency on non-transformed cell physiology. We found that NIH 3T3 fibroblasts with decreased level of S100A6 manifested altered cell morphology and proliferated at a much slower pace than the control cells. Cell cycle analysis showed that a large population of these cells lost the ability to respond to serum and persisted in the G0/G1 phase. Furthermore, fibroblasts with diminished S100A6 level exhibited morphological changes and biochemical features of cellular senescence as revealed by beta-galactosidase and gelatinase assays. Also, S100A6 deficiency induced changes in the actin cytoskeleton and had a profound impact on cell adhesion and migration. Thus, we have shown that the S100A6 protein is involved in multiple aspects of fibroblast physiology and that its presence ensures normal fibroblast proliferation and function.

Multistep pathogenesis of leukemia via the MLL-AF4 chimeric gene/Flt3 gene tyrosine kinase domain (TKD) mutation-related enhancement of S100A6 expression

OBJECTIVE

Concerning MLL-AF4 leukemogenesis, previous mouse models suggest that the tumorigenesis capacity of MLL-AF4 alone is insufficient for causing leukemia. Based on the finding that an Fms-like tyrosine kinase 3 (Flt3) gene mutation in the tyrosine kinase domain (TKD) was observed in approximately 15% of mixed lineage leukemia (MLL), we investigated synergistic leukemogenesis effects of the two genes in vitro.

MATERIALS AND METHODS

In a mouse interleukin-3 (IL-3)-dependent cell line, 32Dc, expression of MLL-AF4 and mutant Flt3 was induced using a lentiviral vector. We analyzed apoptosis induction in the absence of IL-3 and the granulocyte colony-stimulating factor-related induction of differentiation, gene expression profiling, and the mechanism involved in the synergistic effects of MLL-AF4 and Flt3-TKD.

RESULTS

Neither Flt3-expressing 32Dc (32Dc(Flt3-TKD)) nor MLL-AF4-expressing 32Dc (32Dc(MLL-AF4)) acquired IL-3-independent proliferative capacity in semisolid/liquid media. However, Flt3-TKD+MLL-AF4-expressing 32Dc (32Dc(Flt3-TKD+MLL-AF4)) acquired a non-IL-3-dependent proliferative capacity by inhibiting apoptosis in the two media. The 32Dc(Flt3-TKD) and 32Dc(MLL-AF4) cells differentiated into granulocytes in the presence of granulocyte colony-stimulating factor. However, in the 32Dc(Flt3-TKD+MLL-AF4) cells, there was no differentiation. Subsequently, we performed gene expression profiling. The enhancement of Hox genes expression was not identified. However, expression of S100A6 was synergistically enhanced in the presence of both MLL-AF4 and Flt3-TKD genes. Moreover, anti-S100A6 small interfering RNA downregulated leukemic proliferation.

CONCLUSION

We conclude that their synergistic enhancement of S100A6 expression plays an important role in MLL-AF4-associated leukemogenesis.

Expression of S100A6 in cardiac myocytes limits apoptosis induced by tumor necrosis factor-alpha

S100A6 is induced in myocardium post-infarction in vivo and in response to growth factors and inflammatory cytokines in vitro. Forced expression of S100A6 in cardiomyocytes inhibits regulation of cardiac specific gene expression in response to trophic stimulation. To define regulation and function of S100A6, we characterized the human S100A6 promoter and mapped upstream regulatory elements in rat neonatal cardiac myocytes, fibroblasts, and vascular smooth muscle cells and defined a functional role for S100A6 in tumor necrosis factor-alpha-induced myocyte apoptosis. The functional S100A6 promoter was localized to region -167/+134 containing 167 upstream base pairs. The S100A6 promoter is regulated by positive (-361/-167 and -588/-361) and negative (-1371/-1194) elements. Tumor necrosis factor-alpha induced the maximal S100A6 promoter and transcription factor NF-kappaB (p65 subunit). Electrophoretic mobility shift showed that tumor necrosis factor-alpha induced p65 binding to a potential NF-kappaB-binding site at -460/-451. Chromatin immunoprecipitation analysis revealed p65 is recruited to the S100A6 promoter upon tumor necrosis factor-alpha stimulation. The NF-kappaB inhibitor caffeic acid phenethyl ester and mutation of the NF-kappaB-binding site inhibited S100A6 promoter activation by tumor necrosis factor-alpha. Tumor necrosis factor-alpha induced cardiac myocyte apoptosis. Specific inhibition of S100A6 using a small interfering RNA directed against S100A6 potentiated tumor necrosis factor-alpha-induced myocyte apoptosis, whereas overexpression of S100A6 by gene transfer prevented tumor necrosis factor-alpha-induced myocyte apoptosis by interfering with p53 phosphorylation. These results demonstrate that S100A6 is induced by tumor necrosis factor-alpha via an NF-kappaB-dependent mechanism, serving a role in homeostasis to limit tumor necrosis factor-alpha-induced apoptosis by regulating p53 phosphorylation.

Vasopressin-inducible ubiquitin-specific protease 10 increases ENaC cell surface expression by deubiquitylating and stabilizing sorting nexin 3

Adjustment of Na+balance in extracellular fluids is achieved by regulated Na+transport involving the amiloride-sensitive epithelial Na+channel (ENaC) in the distal nephron. In this context, ENaC is controlled by a number of hormones, including vasopressin, which promotes rapid translocation of water and Na+channels to the plasma membrane and long-term effects on transcription of vasopressin-induced and -reduced transcripts. We have identified a mRNA encoding the deubiquitylating enzyme ubiquitin-specific protease 10 (Usp10), whose expression is increased by vasopressin at both the mRNA and the protein level. Coexpression of Usp10 in ENaC-transfected HEK-293 cells causes a more than fivefold increase in amiloride-sensitive Na+currents, as measured by whole cell patch clamping. This is accompanied by a three- to fourfold increase in surface expression of α- and γ-ENaC, as shown by cell surface biotinylation experiments. Although ENaC is well known to be regulated by its direct ubiquitylation, Usp10 does not affect the ubiquitylation level of ENaC, suggesting an indirect effect. A two-hybrid screen identified sorting nexin 3 (SNX3) as a novel substrate of Usp10. We show that it is a ubiquitylated protein that is degraded by the proteasome; interaction with Usp10 leads to its deubiquitylation and stabilization. When coexpressed with ENaC, SNX3 increases the channel's cell surface expression, similarly to Usp10. In mCCDcl1cells, vasopressin increases SNX3 protein but not mRNA, supporting the idea that the vasopressin-induced Usp10 deubiquitylates and stabilizes endogenous SNX3 and consequently promotes cell surface expression of ENaC.

Role of AQP2 in activation of calcium entry by hypotonicity: implications in cell volume regulation

We previously reported in a rat cortical collecting duct cell line (RCCD1) that the presence of aquaporin 2 (AQP2) in the cell membrane is critical for the rapid activation of regulatory volume decrease mechanisms (RVD) (Ford et al. Biol Cell 97: 687–697, 2005). The aim of our present work was to investigate the signaling pathway that links AQP2 to this rapid RVD activation. Since it has been previously described that hypotonic conditions induce intracellular calcium ([Ca2+]i) increases in different cell types, we tested the hypothesis that AQP2 could have a role in activation of calcium entry by hypotonicity and its implication in cell volume regulation. Using a fluorescent probe technique, we studied [Ca2+]iand cell volume changes in response to a hypotonic shock in WT-RCCD1(not expressing aquaporins) and in AQP2-RCCD1(transfected with AQP2) cells. We found that after a hypotonic shock only AQP2-RCCD1cells exhibit a substantial increase in [Ca2+]i. This [Ca2+]iincrease is strongly dependent on extracellular Ca2+and is partially inhibited by thapsigargin (1 μM) indicating that the rise in [Ca2+]ireflects both influx from the extracellular medium and release from intracellular stores. Exposure of AQP2-RCCD1cells to 100 μM gadolinium reduced the increase in [Ca2+]isuggesting the involvement of a mechanosensitive calcium channel. Furthermore, exposure of cells to all of the above described conditions impaired rapid RVD. We conclude that the expression of AQP2 in the cell membrane is critical to produce the increase in [Ca2+]iwhich is necessary to activate RVD in RCCD1cells.

Upregulated expression of S100A6 in human gastric cancer

OBJECTIVE

The expression of S100A6 (calcyclin), a member of the S100 calcium binding protein family, is elevated in a number of malignant tumors, but there have been few reports about its expression in gastric cancer. The aim of this study was to investigate its expression regulations in human gastric cancer and noncancerous mucosa, and the response to chemotherapeutic drugs in the gastric cancer cell line.

MATERIALS AND METHODS

In one matched gastric cancer sample pair, the serial analysis of gene expression (SAGE) experiment was conducted to compare the gene expression profiles between cancerous and adjacent tissues. To detect the expression regulations among more cancerous tissues, microarrays were carried out and real-time RT-PCR was conducted to validate the results. At the protein level, Western blot and tissue microarray (TMA) examination were further used to verify S100A6 expression. The regulation detection of S100A6 with flurouracil and doxorubicin at the mRNA and protein level was performed in the SGC7901 cell line.

RESULTS

With the SAGE strategy, five times more S100A6 tags were identified in cancer tissues than in normal tissues. With the cDNA microarray, S100A6 was found to be significantly upregulated in 21 of 42 (50%) nonselective gastric cancers. In 10 other paired samples, the upregulation of S100A6 was consolidated with RT-PCR and Western blot analysis as well. A total of 14 endoscopy-sectioned gastric noncancerous lesions and corresponding normal gastric mucosa were also applied to profile the gene expression; both cDNA microarray and RT-PCR demonstrated no significant alterations of S100A6 at the mRNA level. TMA examination showed that 34 of 52 (65.4%) cancer samples were positively stained, while only 17 of 80 (21.3%) noncancerous lesions were positively detected and all nine normal mucosae were detected to be negative. An in vitro experiment showed that in the gastric cell line SGC-7901, S100A6 mRNA was detected to be upregulated from 24 to 72 h after treatment with 5 mg/L 5-flurouracil or 0.3 mg/L doxorubicin, and there were two wave upregulations of the S100A6 protein.

CONCLUSION

The observed regulated expression of S100A6 suggests that it is associated with gastric cancer tumorigenesis and quantitation of S100A6 is a promising tool for diagnosis of gastric cancer.

LC-MS/MS analysis of apical and basolateral plasma membranes of rat renal collecting duct cells

We used biotinylation and streptavidin affinity chromatography to label and enrich proteins from apical and basolateral membranes of rat kidney inner medullary collecting ducts (IMCDs) prior to LC-MS/MS protein identification. To enrich apical membrane proteins and bound peripheral membrane proteins, IMCDs were perfusion-labeled with primary amine-reactive biotinylation reagents at 2 degrees C using a double barreled pipette. The perfusion-biotinylated proteins and proteins bound to them were isolated with CaptAvidin-agarose beads, separated with SDS-PAGE, and sliced into continuous gel pieces for LC-MS/MS protein identification (LTQ, Thermo Electron Corp.). 17 integral and glycosylphosphatidylinositol (GPI)-linked membrane proteins and 44 non-integral membrane proteins were identified. Immunofluorescence confocal microscopy confirmed ACVRL1, H(+)/K(+)-ATPase alpha1, NHE2, and TauT expression in the IMCDs. Basement membrane and basolateral membrane proteins were biotinylated via incubation of IMCD suspensions with biotinylation reagents on ice. 23 integral and GPI-linked membrane proteins and 134 non-integral membrane proteins were identified. Analyses of non-integral membrane proteins preferentially identified in the perfusion-biotinylated and not in the incubation-biotinylated IMCDs revealed protein kinases, scaffold proteins, SNARE proteins, motor proteins, small GTP-binding proteins, and related proteins that may be involved in vasopressin-stimulated AQP2, UT-A1, and ENaC regulation. A World Wide Web-accessible database was constructed of 222 membrane proteins (integral and GPI-linked) from this study and prior studies.

Binding and functional characteristics of two E-box motifs within the S100A6 (calcyclin) gene promoter

S100A6 (calcyclin) is a small calcium-binding protein of the S100 family often associated with cancer and metastasis. We have previously shown that the E-box sequence at position -283/-278 of the S100A6 gene promoter interacts with USF transcription factor and contributes to promoter transcriptional activity. We now present evidence that a second E-box motif at position -593/-588 of the promoter also binds USF and that the USF1/USF2 heterodimer is the prevailing dimeric form of the transcription factor bound. Using the chromatin immunoprecipitation assay (ChIP), we show that USF is bound in vivo to the E-box regulatory element(s). Depletion of the endogenous USF pool by means of a decoy oligonucleotide evokes a severe inhibition of S100A6 gene promoter activity. Furthermore, we show that S100A6 gene promoter activity can be stimulated by palmitate and that mutation of the -283/-278 E-box sequence completely blocks this stimulation.

Transcriptome analysis and kidney research: Toward systems biology

An enormous amount of data has been generated in kidney research using transcriptome analysis techniques. In this review article, we first describe briefly the principles and major characteristics of several of these techniques. We then summarize the progress in kidney research that has been made by using transcriptome analysis, emphasizing the experience gained and the lessons learned. Several technical issues regarding DNA microarray are highlighted because of the rapidly increased use of this technology. It appears clear from this brief survey that transcriptome analysis is an effective and important tool for question-driven exploratory science. To further enhance the power of this and other high throughput, as well as conventional approaches, in future studies of the kidney, we propose a multidimensional systems biology paradigm that integrates investigation at multiple levels of biologic regulation toward the goal of achieving a global understanding of physiology and pathophysiology.

High nuclear S100A6 (Calcyclin) is significantly associated with poor survival in pancreatic cancer patients

Recent studies have reported elevated levels of S100A6 in pancreatic ductal adenocarcinoma cells. Here, we describe a detailed analysis of S100A6 expression in benign (n = 32), malignant (n = 60), and premalignant pancreatic ductal cells [96 pancreatic intraepithelial neoplasias (PanIN) from 46 patients]. S100A6 staining was more intense in malignant cells than in benign cells (P = 0.0001). In malignant cells, staining was higher in the nucleus than in the cytoplasm (P = 0.003). Univariate analysis revealed a significant decrease in survival time for patients with high levels of nuclear (P = 0.01) but not cytoplasmic (P = 0.20) S100A6. No evidence was found for an association between nuclear S100A6 expression and other variables, including gender, age at surgery, tumor size or grade, nodal metastases, resection margin, vascular invasion, perineural invasion, p53 or Smad4 levels (both linked to survival in previous studies), or the p65 subunit of nuclear factor-kappaB (a potential regulator of S100A6). Although nodal metastases and resection margin involvement were also associated with poor survival (P = 0.06 in both cases), multivariate analysis suggests that nuclear S100A6 is a significant independent indicator of survival (P = 0.003). Whereas PanIN 1a lesions showed a general absence of S100A6 staining, there was a progressive increase in the proportion of positively stained PanINs with increasing PanIN grade. In particular, we observed an increase in the frequency and intensity of nuclear staining. Our results suggest that up-regulation of S100A6 is an early event in pancreatic cancer development and that elevated levels of nuclear S100A6 may affect clinical outcome.

Astrocytic calcium/zinc binding protein S100A6 over expression in Alzheimer's disease and in PS1/APP transgenic mice models

Astrocytes recruitment and activation are a hallmark of many neurodegenerative diseases including Alzheimer's disease (AD). We have previously observed an overexpression for S100A6 protein, a Ca(2+)/Zn(2+) binding protein presenting more affinity for zinc than for calcium, in amyotrophic lateral sclerosis (ALS). Here we demonstrated in AD patients but also in two different AD mouse models, that astrocytic S100A6 protein was homogeneously up-regulated within the white matter. However, within the grey matter, almost all S100A6 immunoreactivity was concentrated in astrocytes surrounding the Abeta amyloid deposits of senile plaques. These S100A6 neocortex labelled astrocytes were also positive for the glial fibrillary acidic protein (GFAP) and S100B protein. Contrasting with S100A6, the distribution for S100B and GFA astrocytic labelled cells was not restricted to the Abeta amyloid deposit in grey matter, but widely distributed throughout the neocortex. Coupling the knowledge that biometals such as zinc are highly concentrated in the amyloid deposits in AD and S100A6 having a high affinity for Zn(2+) may suggest that S100A6 plays a role in AD neuropathology.

Identification of vasopressin-induced genes in AQP2-transfected MDCK cells by suppression subtractive hybridization

Arginine vasopressin (AVP) plays a major role in the modulation of water reabsorption in mammalian kidney. In addition to short-term regulation of aquaporin 2 (AQP2) trafficking, AVP also has long-term effects to regulate the expression of AQP2 in renal collecting duct. However, the detailed mechanism of the long-term effects of AVP in kidney remains to be elucidated. We have searched for genes induced by AVP using the polymerase chain reaction-based suppression subtractive hybridization technique in AVP-responsive AQP2-transfected MDCK cells. We found that the expression of the genes such as VIP17/MAL, annexin II, stimulatory GTP binding protein, tubulin, and mitochondrial ATP synthase was induced by AVP treatment for 4h. These results suggest that AVP might induce the expression of several genes related to the apical targeting of newly synthesized AQP2 as well as that of AQP2 for the long-term modification of water permeability in renal collecting duct.

Endocrine Disorders of Sodium Regulation

Salt and water homoeostasis is tightly regulated by a variety of control mechanisms with the adrenal steroid hormone aldosterone playing a central role. Defects or disturbances in these systems lead to either salt loss, which is life threatening in the neonatal period, or sodium retention causing hypertension. Rapid and accurate diagnosis is required to avoid severe complications. During the last few years molecular genetic advances have been identified as the basic genetic defects for a number of clinical syndromes. This knowledge has considerably increased our understanding of the basic pathways involved in sodium and water homoeostasis and of the pathophysiology of these syndromes, particularly the hypertension. In this review we have summarized the biochemical, physiological and genetic basis for clinical syndromes presenting with salt loss and failure to thrive as well as the rare but important genetic syndromes causing sodium retention and hypertension. Early diagnosis and identification will help to prevent severe complications, but it has to be emphasized that the complicated cascade of aldosterone action is still relatively poorly understood. Further syndromes may exist which once identified will help to better understand the basic physiology of aldosterone action.

Proteomic analysis of long-term vasopressin action in the inner medullary collecting duct of the Brattleboro rat

Vasopressin regulates water and solute transport in the renal collecting duct. In addition to short-term regulation of aquaporin-2 trafficking, vasopressin also has long-term effects to regulate the abundances of aquaporins-2 and -3 and beta- and gamma-subunits of the epithelial sodium channel in collecting duct principal cells. To investigate further the direct and indirect long-term regulatory actions of vasopressin in the inner medullary collecting duct (IMCD), we used a proteomic approach [difference gel electrophoresis (DIGE) coupled with MALDI-TOF identification of differentially expressed protein spots]. DDAVP or vehicle was infused subcutaneously in Brattleboro rats for 3 days, and IMCD cells were purified from the inner medullas for proteomic analysis. Forty-three proteins were found to be regulated in response to vasopressin infusion, including 18 that were increased in abundance, 22 that were decreased, and 3 that were shifted in the gel, presumably because of posttranslational modification. Immunocytochemistry confirmed collecting duct expression of several of the proteins that were identified. Immunoblot analysis of nine of the proteins confirmed the changes seen by the DIGE method. Of these nine proteins, six were increased in response to DDAVP infusion: nitric oxide synthase-2 (NOS2), GRP78, heat shock protein-70, annexin II, glutaminase, and cathepsin D. The remaining three were decreased in response to DDAVP: aldehyde reductase I, adenylyl cyclase VI, and carbonic anhydrase II. The findings point to a role for vasopressin in the coordinate regulation of several determinants of nitric oxide levels (NOS2, arginase II, NADPH oxidase) and of proteins potentially involved in vasopressin escape (adenylyl cyclase VI and G protein-coupled receptor kinase 4).

Calcyclin (S100A6) regulates pulmonary fibroblast proliferation, morphology, and cytoskeletal organization in vitro

Calcyclin (S100A6) is a member of the S100A family of calcium binding proteins. While the precise function of calcyclin is unknown, calcyclin expression is associated with cell proliferation and calcyclin is expressed in several types of cancer phenotypes. In the present study, the functional role of calcyclin was further elucidated in pulmonary fibroblasts. Antisense S100A6 RNA expression inhibited serum and mechanical strain-induced fibroblast proliferation. This attenuated proliferative response was accompanied by a flattened, spread cell morphology, and disruption of tropomyosin labeled microfilaments. Changes in cytoskeletal organization did not correspond with a decrease in tropomyosin levels. These observations suggest a role for calcyclin in modulating calcium dependent signaling events that regulate progression through the cell cycle. J. Cell. Biochem. 88: 848-854, 2003.

Silencing of TonEBP/NFAT5 transcriptional activator by RNA interference

TonEBP is a transcriptional activator that is expressed throughout development in many tissues and cell types. In the kidney medulla, TonEBP appears to be an important local regulator of differentiation by virtue of stimulating several genes. To study the function of TonEBP, two small interfering RNA (siRNA) duplexes were developed that reduced TonEBP expression effectively via RNA interference. The silencing lasted only 3 d after introduction of the TonEBP-siRNA's. As expected, TonEBP-driven reporter gene expression and expression of the sodium/myo-inositol cotransproter (SMIT), aldose reductase (AR) and heat shock protein 70 (HSP70) mRNA were significantly decreased in cells where TonEBP expression was silenced. These data provide direct evidence that the SMIT, AR, and HSP70 genes are targets of TonEBP, although the potential role of other proteins, such as accessory proteins, cannot be excluded. The TonEBP-siRNA is an effective tool that should prove useful in the investigation of loss-of-function relationship in cells.