Cloning and identification of the gene gob-5, which is expressed in intestinal goblet cells in mice

Evolutionarily conserved properties of CLCA proteins 1, 3 and 4, as revealed by phylogenetic and biochemical studies in avian homologues

Species-specific diversities are particular features of mammalian chloride channel regulator, calcium activated (CLCA) genes. In contrast to four complex gene clusters in mammals, only two CLCA genes appear to exist in chickens. CLCA2 is conserved in both, while only the galline CLCA1 (gCLCA1) displays close genetic distance to mammalian clusters 1, 3 and 4. In this study, sequence analyses and biochemical characterizations revealed that gCLCA1 as a putative avian prototype shares common protein domains and processing features with all mammalian CLCA homologues. It has a transmembrane (TM) domain in the carboxy terminal region and its mRNA and protein were detected in the alimentary canal, where the protein was localized in the apical membrane of enterocytes, similar to CLCA4. Both mammals and birds seem to have at least one TM domain containing CLCA protein with complex glycosylation in the apical membrane of enterocytes. However, some characteristic features of mammalian CLCA1 and 3 including entire protein secretion and expression in cell types other than enterocytes seem to be dispensable for chicken. Phylogenetic analyses including twelve bird species revealed that avian CLCA1 and mammalian CLCA3 form clades separate from a major branch containing mammalian CLCA1 and 4. Overall, our data suggest that gCLCA1 and mammalian CLCA clusters 1, 3 and 4 stem from a common ancestor which underwent complex gene diversification in mammals but not in birds.

Mouse TMCO5 is localized to the manchette microtubules involved in vesicle transfer in the elongating spermatids

As a result of a high-throughput in situ hybridization screening for adult mouse testes, we found that the mRNA for Tmco5 is expressed in round and elongating spermatids. Tmco5 belongs to the Tmco (Transmembrane and coiled-coil domains) gene family and has a coiled-coil domain in the N-terminal and a transmembrane domain in the C-terminal region. A monoclonal antibody raised against recombinant TMCO5 revealed that the protein is expressed exclusively in the elongating spermatids of step 9 to 12 and is localized to the manchette, a transiently emerging construction, which predominantly consists of cytoskeleton microtubules and actin filaments. This structure serves in the transport of Golgi-derived non-acrosomal vesicles. Moreover, induced expression of TMCO5 in CHO cells resulted in the co-localization of TMCO5 with β-tubulin besides the reorganization of the Golgi apparatus. Judging from the results and considering the domain structure of TMCO5, we assume that Tmco5 may have a role in vesicle transport along the manchette.

A sticky end for gastrointestinal helminths; the role of the mucus barrier

Gastrointestinal (GI) nematodes are a group of successful multicellular parasites that have evolved to coexist within the intestinal niche of multiple species. It is estimated that over 10% of the world's population are chronically infected by GI nematodes, making this group of parasitic nematodes a major burden to global health. Despite the large number of affected individuals, there are few effective treatments to eradicate these infections. Research into GI nematode infections has primarily focused on defining the immunological and pathological consequences on host protection. One important but neglected aspect of host protection is mucus, and the concept that mucus is just a simple barrier is no longer tenable. In fact, mucus is a highly regulated and dynamic-secreted matrix, underpinned by a physical hydrated network of highly glycosylated mucins, which is increasingly recognized to have a key protective role against GI nematode infections. Unravelling the complex interplay between mucins, the underlying epithelium and immune cells during infection are a major challenge and are required to fully define the protective role of the mucus barrier. This review summarizes the current state of knowledge on mucins and the mucus barrier during GI nematode infections, with particular focus on murine models of infection.

CCN3 Expression Marks a Sulfomucin-nonproducing Unique Subset of Colonic Goblet Cells in Mice

Intestinal goblet cells are characterized by their unique morphology and specialized function to secrete mucins. Although it is known that they are a heterogeneous population of cells, there have been few studies that relate the expression of a particular gene with functionally distinct subpopulations of intestinal goblet cells. Here we show that CCN3, a gene encoding a member of the CCN family proteins, is induced by inhibition of Notch signaling in colonic epithelial cells and expressed in goblet cells in mice. We demonstrate that CCN3 expression is confined to a subpopulation of goblet cells in the lower crypt of the proximal and middle colon. In addition, CCN3+ cells in the colon correlate well with the cells that are positive for alcian blue (AB) staining but negative for high-iron diamine (HID) staining in histology. We also show that CCN3+ cells, which are absent in the normal distal colon, transiently and ectopically emerge in regenerating crypts during the repair phase of DSS-induced colitis model. Our study thus suggests that CCN3 labels a unique subpopulation of sulfomucin-nonproducing colonic goblet cells that function in both normal and diseased colonic epithelia.

Antibody to mCLCA3 suppresses symptoms in a mouse model of asthma

Background

Asthma is a complex and heterogeneous chronic inflammatory disorder that is associated with mucous cell metaplasia and mucus hypersecretion. Functional genomic analysis indicates that mucous cell metaplasia and mucus hypersecretion depend on members of the calcium-activated chloride channel (CLCA) gene family. It has been reported that the inhibition of CLCAs could relieve the symptoms of asthma. Thus, the mCLCA3 antibody may be a promising strategy to treat allergic diseases such as asthma.

Methods

We constructed asthmatic mouse models of OVA-induced chronic airway inflammatory disorder to study the function of the mCLCA3 antibody. Airway inflammation was measured by HE staining; goblet cell hyperplasia and mucus hypersecretion were detected by PAS staining; muc5ac, IL-13, IFN-γ levels in bronchoalveolar lavage fluid (BALF) were examined by ELISA; Goblet cell apoptosis was measured by TUNEL assay and alcian blue staining; mCLCA3, Bcl-2 and Bax expression were detected by RT-PCR, Western blotting and immunohistochemical analysis.

Results

In our study, mice treated with mCLCA3 antibody developed fewer pathological changes compared with control mice and asthmatic mice, including a remarkable reduction in airway inflammation, the number of goblet cells and mCLCA3 expression in lung tissue. The levels of muc5ac and IL-13 were significantly reduced in BALF. We also found that the rate of goblet cell apoptosis was increased after treatment with mCLCA3 antibody, which was accompanied by an increase in Bax levels and a decrease in Bcl-2 expression in goblet cells.

Conclusions

Taken together, our results indicate that mCLCA3 antibody may have the potential as an effective pharmacotherapy for asthma.

Lineage-specific expression of bestrophin-2 and bestrophin-4 in human intestinal epithelial cells

Intestinal epithelial cells (IECs) regulate the absorption and secretion of anions, such as HCO3^- or Cl^-. Bestrophin genes represent a newly identified group of calcium-activated Cl^- channels (CaCCs). Studies have suggested that, among the four human bestrophin-family genes, bestrophin-2 (BEST2) and bestrophin-4 (BEST4) might be expressed within the intestinal tissue. Consistently, a study showed that BEST2 is expressed by human colonic goblet cells. However, their precise expression pattern along the gastrointestinal tract, or the lineage specificity of the cells expressing these genes, remains largely unknown. Here, we show that BEST2 and BEST4 are expressed in vivo, each in a distinct, lineage-specific manner, in human IECs. While BEST2 was expressed exclusively in colonic goblet cells, BEST4 was expressed in the absorptive cells of both the small intestine and the colon. In addition, we found that BEST2 expression is significantly down-regulated in the active lesions of ulcerative colitis, where goblet cells were depleted, suggesting that BEST2 expression is restricted to goblet cells under both normal and pathologic conditions. Consistently, the induction of goblet cell differentiation by a Notch inhibitor, LY411575, significantly up-regulated the expression of not BEST4 but BEST2 in MUC2-positive HT-29 cells. Conversely, the induction of absorptive cell differentiation up-regulated the expression of BEST4 in villin-positive Caco-2 cells. In addition, we found that the up- or down-regulation of Notch activity leads to the preferential expression of either BEST4 or BEST2, respectively, in LS174T cells. These results collectively confirmed that BEST2 and BEST4 could be added to the lineage-specific genes of humans IECs due to their abilities to clearly identify goblet cells of colonic origin and a distinct subset of absorptive cells, respectively.

IL-22 mediates goblet cell hyperplasia and worm expulsion in intestinal helminth infection

Type 2 immune responses are essential in protection against intestinal helminth infections. In this study we show that IL-22, a cytokine important in defence against bacterial infections in the intestinal tract, is also a critical mediator of anti-helminth immunity. After infection with Nippostrongylus brasiliensis, a rodent hookworm, IL-22-deficient mice showed impaired worm expulsion despite normal levels of type 2 cytokine production. The impaired worm expulsion correlated with reduced goblet cell hyperplasia and reduced expression of goblet cell markers. We further confirmed our findings in a second nematode model, the murine whipworm Trichuris muris. T.muris infected IL-22-deficient mice had a similar phenotype to that seen in N.brasiliensis infection, with impaired worm expulsion and reduced goblet cell hyperplasia. Ex vivo and in vitro analysis demonstrated that IL-22 is able to directly induce the expression of several goblet cell markers, including mucins. Taken together, our findings reveal that IL-22 plays an important role in goblet cell activation, and thus, a key role in anti-helminth immunity.

International Union of Basic and Clinical Pharmacology. LXXXV: calcium-activated chloride channels

Calcium-activated chloride channels (CaCCs) are widely expressed in various tissues and implicated in physiological processes such as sensory transduction, epithelial secretion, and smooth muscle contraction. Transmembrane proteins with unknown function 16 (TMEM16A) has recently been identified as a major component of CaCCs. Detailed molecular analysis of TMEM16A will be needed to understand its structure-function relationships. The role this channel plays in physiological systems remains to be established and is currently a subject of intense investigation.

Impact of obesity and leptin on protein expression profiles in mouse colon

BACKGROUND

Elevated leptin levels in obesity are associated with increased risk of colon pathology, implicating leptin signaling in colon disease. However, leptin-regulated processes in the colon are currently uncharacterized. Previously, we demonstrated that leptin receptors are expressed on colon epithelium and that increased adiposity and elevated plasma leptin in rats are associated with perturbed metabolism in colon tissue. Thus, we hypothesize that obesity disrupts expression of proteins regulated by leptin in the colon.

METHODS

A proteomic analysis was conducted to investigate firstly, differences in the colon of mice lacking leptin and leptin signaling (ob/ob and db/db, respectively) by comparing protein expression profiles with wild-type mice. Secondly, responses to leptin challenge in wild-type mice and ob/ob mice were compared to identify leptin-regulated proteins and associated cellular processes.

RESULTS

Forty proteins were identified with significantly altered expression patterns associated with differences in leptin status in comparisons between all groups of mice. These proteins are associated with calcium binding, cell cycle, cell proliferation, electron transport chain, energy metabolism, protein folding and transport, redox regulation, structural proteins, and proteins involved in transport and regulation of mucus production.

CONCLUSIONS

This study provides evidence that obesity and leptin significantly alter protein profiles of a number of proteins linked to cellular processes in colon tissues that may be linked to the increased risk of colon pathology associated with obesity.

Proteomic analyses of the two mucus layers of the colon barrier reveal that their main component, the Muc2 mucin, is strongly bound to the Fcgbp protein

The colon epithelium is protected from the luminal microbes as recently revealed by an inner firmly attached mucus layer impervious to bacteria and an outer loose mucus layer that is the habitat of bacteria. For an additional understanding of these layers, we analyzed the protein composition of these two mucus layers from the mouse colon. Proteomics using nano-LC-MS and MS/MS revealed more than 1000 protein entries. As the mucus layers contain detached cells, a majority of the proteins had an intracellular origin. However, at least 44 entries were described as secreted proteins and predicted to be mucus constituents together with extracellular/plasma and bacterial proteins, the latter largely in the loose mucus layer. A major protein was the Muc2 mucin that by its net-like disulfide-bonded polymer structure builds the mucus. When guanidinium chloride insoluble Muc2 units were analyzed, N-terminal parts of the Fc-gamma binding protein (Fcgbp) was found to be covalently attached in mouse and human colon, whereas its C-terminus was lost by reducing the disulfide bonds. In conclusion, the Fcgbp protein is probably cleaved at GD/PH and covalently attached to Muc2 via one or several of its von Willebrand D domains.

The role of CLCA proteins in inflammatory airway disease

Inflammatory airway diseases such as asthma and chronic obstructive pulmonary disease (COPD) exhibit stereotyped traits that are variably expressed in each person. In experimental mouse models of chronic lung disease, these individual disease traits can be genetically segregated and thereby linked to distinct determinants. Functional genomic analysis indicates that at least one of these traits, mucous cell metaplasia, depends on members of the calcium-activated chloride channel (CLCA) gene family. Here we review advances in the biochemistry of the CLCA family and the evidence of a role for CLCA family members in the development of mucous cell metaplasia and possibly airway hyperreactivity in experimental models and in humans. On the basis of this information, we develop the model that CLCA proteins are not integral membrane proteins with ion channel function but instead are secreted signaling molecules that specifically regulate airway target cells in healthy and disease conditions.

The inner of the two Muc2 mucin-dependent mucus layers in colon is devoid of bacteria

We normally live in symbiosis with approximately 10(13) bacteria present in the colon. Among the several mechanisms maintaining the bacteria/host balance, there is limited understanding of the structure, function, and properties of intestinal mucus. We now demonstrate that the mouse colonic mucus consists of two layers extending 150 mum above the epithelial cells. Proteomics revealed that both of these layers have similar protein composition, with the large gel-forming mucin Muc2 as the major structural component. The inner layer is densely packed, firmly attached to the epithelium, and devoid of bacteria. In contrast, the outer layer is movable, has an expanded volume due to proteolytic cleavages of the Muc2 mucin, and is colonized by bacteria. Muc2(-/-) mice have bacteria in direct contact with the epithelial cells and far down in the crypts, explaining the inflammation and cancer development observed in these animals. These findings show that the Muc2 mucin can build a mucus barrier that separates bacteria from the colon epithelia and suggest that defects in this mucus can cause colon inflammation.

Interleukin-4, interleukin-13, signal transducer and activator of transcription factor 6, and allergic asthma

Interleukin (IL)-4 and IL-13 share many biological activities. To some extent, this is because they both signal via a shared receptor, IL-4Ralpha. Ligation of IL-4Ralpha results in activation of Signal Transducer and Activator of Transcription factor 6 (STAT6) and Insulin Receptor Substrate (IRS) molecules. In T- and B-cells, IL-4Ralpha signaling contributes to cell-mediated and humoral aspects of allergic inflammation. It has recently become clear that IL-4 and IL-13 produced in inflamed tissues activate signaling in normally resident cells of the airway. The purpose of this review is to critically evaluate the contributions of IL-4- and IL-13-induced tissue responses, especially those mediated by STAT6, to some of the pathologic features of asthma including eosinophilic inflammation, airway hyperresponsiveness, subepithelial fibrosis and excessive mucus production. We also review the functions of some recently identified IL-4- and/or IL-13-induced mediators that provide some detail on molecular mechanisms and suggest an important contribution to host defense.

The role of ET(A) and ET(B) receptor antagonists in acute and allergic inflammation in mice

In this study, we investigated the effects of the selective ET(A) (BQ-123) and ET(B) (BQ-788) receptor antagonists for endothelin-1 (ET-1) against several flogistic agent-induced paw edema formation and ovalbumin-induced allergic lung inflammation in mice. The intraplantar injection of BQ-123, but not BQ-788, significantly inhibited carrageenan-, PAF-, ET-1- and bradykinin-induced paw edema formation. The obtained inhibitions (1h after the inflammatory stimulus) were 79+/-5%, 55+/-4%, 55+/-6% and 74+/-4%, respectively. In carrageenan-induced paw edema, the mean ID(50) value for BQ-123 was 0.77 (0.27-2.23)nmol/paw. The neutrophil influx induced by carrageenan or PAF was reduced by BQ-123, with inhibitions of 55+/-2% and 72+/-4%, respectively. BQ-123 also inhibited the indirect macrophage influx induced by carrageenan (55+/-6%). However, BQ-788 failed to block the cell influx caused by either of these flogistic agents. When assessed in the bronchoalveolar lavage fluid in a murine model of asthma, both BQ-123 and BQ-788 significantly inhibited ovalbumin-induced eosinophil recruitment (78+/-6% and 71+/-8%), respectively. Neither neutrophil nor mononuclear cell counts were significantly affected by these drugs. Our findings indicate that ET(A), but not ET(B), selective ET-1 antagonists are capable of preventing the acute inflammatory responses induced by carrageenan, PAF, BK and ET-1. However, both ET(A) and ET(B) receptor antagonists were found to be effective in inhibiting the allergic response in a murine model of asthma.

The intestinal epithelium: sensors to effectors in nematode infection

The role of the intestinal epithelium as part of the physical barrier to infection is well established alongside its central roles in food absorption, sensing nutrients, and water balance. Nematodes are one of the most common types of pathogen to dwell in the intestine. This article reviews recent data that have identified crucial roles for intestinal epithelial cells in sensing these kinds of pathogens and initiating innate responses, which qualitatively influence adaptive immune responses against them. Moreover, it is now clear that the epithelium itself--in addition to the cells that lie within it--are key to many of the protective mechanisms that result in expulsion of these large multicellular parasites from the intestine. An understanding of the IEC and intraepithelial leukocyte response is crucial to both development of mucosal vaccines, and the mechanisms that underlie the emerging use of intestinal dwelling helminths for therapeutic treatments of inflammatory and autoimmune disease.

Innate immune response mechanisms in the intestinal epithelium: potential roles for mast cells and goblet cells in the expulsion of adult Trichinella spiralis

SUMMARYGastrointestinal infection with the nematode Trichinella spiralis is accompanied by a rapid and reversible expansion of the mucosal mast cell and goblet cell populations in the intestinal epithelium, which is associated with the release of their mediators into the gut lumen. Both goblet cell and mast cell hyperplasia are highly dependent on mucosal T-cells and augmented by the cytokines IL-4 and IL-13. However, the contribution of both mast and goblet cells, and the mediators they produce, to the expulsion of the adults of T. spiralis is only beginning to be elucidated through studies predominantly employing T. spiralis-mouse models. In the present article, we review the factors proposed to control T. spiralis-induced mucosal mast cell (MMC) and goblet cell differentiation in the small intestine, and focus on some key MMC and goblet cell effector molecules which may contribute to the expulsion of adult worms and/or inhibition of larval development.

Murine mCLCA6 is an integral apical membrane protein of non-goblet cell enterocytes and co-localizes with the cystic fibrosis transmembrane conductance regulator

The CLCA family of proteins consists of a growing number of structurally and functionally diverse members with distinct expression patterns in different tissues. Several CLCA homologs have been implicated in diseases with secretory dysfunctions in the respiratory and intestinal tracts. Here we present biochemical protein characterization and details on the cellular and subcellular expression pattern of the murine mCLCA6 using specific antibodies directed against the amino- and carboxy-terminal cleavage products of mCLCA6. Computational and biochemical characterizations revealed protein processing and structural elements shared with hCLCA2 including anchorage in the apical cell membrane by a transmembrane domain in the carboxy-terminal subunit. A systematic light- and electron-microscopic immunolocalization found mCLCA6 to be associated with the microvilli of non-goblet cell enterocytes in the murine small and large intestine but in no other tissues. The expression pattern was confirmed by quantitative RT-PCR following laser-capture microdissection of relevant tissues. Confocal laser scanning microscopy colocalized the mCLCA6 protein with the cystic fibrosis transmembrane conductance regulator CFTR at the apical surface of colonic crypt cells. Together with previously published functional data, the results support a direct or indirect role of mCLCA6 in transepithelial anion conductance in the mouse intestine.

Amelioration of cystic fibrosis intestinal mucous disease in mice by restoration of mCLCA3

BACKGROUND & AIMS

Mice deficient of the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) exhibit severe intestinal lesions, particularly mucous overproduction/secretion and accumulation, which is similar to meconium ileus in CF patients. Moreover, severity of the intestinal disease in CF mice is strongly influenced by genetic modifiers, and CFTR deficiency affects the expression of multiple secondary genes that may impact on the phenotype. The murine orthologue of human hCLCA1 (mCLCA3) is expressed by goblet cells and implicated in their normal function, particularly with mucus production/secretion that is exaggerated in CF; however, its influence on the CF intestinal disease, although suggested, remains unclear.

METHODS

To investigate the role of mCLCA3 on the CF intestinal disease in mice, its expression in this tissue has been assessed, and a CF mouse line maintaining elevated mCLCA3 levels has been developed and comprehensively characterized.

RESULTS

Expression of mCLCA3 is significantly reduced in CF mouse intestines, although the number of goblet cells is elevated, indicating marked reduction per cell. Importantly, correction of this deficiency results in amelioration of the mucous-based disease leading to a marked improvement of intestinal pathology and survival, although goblet cell hyperplasia and hypertrophy were augmented. This intestinal amelioration did not appear to be related to rectification of the CF electrophysiologic defect.

CONCLUSIONS

mCLCA3 has a role in intestinal goblet cell function that includes modification of the mucous properties and/or secretion that are altered in CF. Thus, elevation of mCLCA3 (hCLCA1) levels could provide a means to reduce intestinal mucous-based lesions in CF and related diseases.

IL-13 mediates in vivo IL-9 activities on lung epithelial cells but not on hematopoietic cells

Increased IL-9 expression, either systemically or under the control of lung-specific promoter, induces an asthma-like phenotype, including mucus overproduction, mastocytosis, lung eosinophilia, and airway hyperresponsiveness. These activities correlate with increased production of other Th2 cytokines such as IL-4, IL-5, and IL-13 in IL-9 Tg mice. To determine the exact role of IL-13 in this phenotype, mice overexpressing IL-9 were crossed with IL-13-deficient mice. In these animals, IL-9 could still induce mastocytosis and B lymphocyte infiltration of the lungs. Although IL-9-induced eosinophilia in the peritoneal cavity was not diminished in the absence of IL-13, IL-13 was required for IL-9 to increase eotaxin expression and lung eosinophilia. Mucus production and up-regulation of lung epithelial genes upon IL-9 overexpression were completely abolished in the absence of IL-13. Using hemopoietic cell transfer experiments with recipients that overexpressed IL-9 but were deficient in the IL-9 receptor (IL-9R), we could demonstrate that the effect of IL-9 on lung epithelial cells is indirect and could be fully restored by transfer of hemopoietic cells expressing IL-9R. Mucus production by lung epithelial cells was only up-regulated when hemopoietic cells simultaneously expressed functional IL-9R and IL-13 genes, indicating that IL-13 is not a cofactor but a direct mediator of the effect of IL-9 on lung epithelial cells. Taken together, these data indicate that IL-9 can promote asthma through IL-13-independent pathways via expansion of mast cells, eosinophils, and B cells, and through induction of IL-13 production by hemopoietic cells for mucus production and recruitment of eosinophils by lung epithelial cells.

Inhibiting pollen reduced nicotinamide adenine dinucleotide phosphate oxidase-induced signal by intrapulmonary administration of antioxidants blocks allergic airway inflammation

BACKGROUND

Ragweed extract (RWE) contains NADPH oxidases that induce oxidative stress in the airways independent of adaptive immunity (signal 1) and augment antigen (signal 2)-induced allergic airway inflammation.

OBJECTIVE

To test whether inhibiting signal 1 by administering antioxidants inhibits allergic airway inflammation in mice.

METHODS

The ability of ascorbic acid (AA), N-acetyl cystenine (NAC), and tocopherol to scavenge pollen NADPH oxidase-generated reactive oxygen species (ROS) was measured. These antioxidants were administered locally to inhibit signal 1 in the airways of RWE-sensitized mice. Recruitment of inflammatory cells, mucin production, calcium-activated chloride channel 3, IL-4, and IL-13 mRNA expression was quantified in the lungs.

RESULTS

Antioxidants inhibited ROS generation by pollen NADPH oxidases and intracellular ROS generation in cultured epithelial cells. AA in combination with NAC or Tocopherol decreased RWE-induced ROS levels in cultured bronchial epithelial cells. Coadministration of antioxidants with RWE challenge inhibited 4-hydroxynonenal adduct formation, upregulation of Clca3 and IL-4 in lungs, mucin production, recruitment of eosinophils, and total inflammatory cells into the airways. Administration of antioxidants with a second RWE challenge also inhibited airway inflammation. However, administration of AA+NAC 4 or 24 hours after RWE challenge failed to inhibit allergic inflammation.

CONCLUSION

Signal 1 plays a proinflammatory role during repeated exposure to pollen extract. We propose that inhibiting signal 1 by increasing antioxidant potential in the airways may be a novel therapeutic strategy to attenuate pollen-induced allergic airway inflammation.

CLINICAL IMPLICATIONS

Administration of antioxidants in the airways may constitute a novel therapeutic strategy to prevent pollen induced allergic airway inflammation.

The mRNA coding for Xenopus glutamate receptor interacting protein 2 (XGRIP2) is maternally transcribed, transported through the late pathway and localized to the germ plasm

Using a large-scale in situ hybridization screening, we found that the mRNA coding for Xenopus glutamate receptor interacting protein 2 (XGRIP2) was localized to the germ plasm of Xenopus laevis. The mRNA is maternally transcribed in oocytes and, during maturation, transported to the vegetal germ plasm through the late pathway where VegT and Vg1 mRNAs are transported. In the 3'-untranslated region (UTR) of the mRNA, there are clusters of E2 and VM1 localization motifs that were reported to exist in the mRNAs classified as the late pathway group. With in situ hybridization to the sections of embryos, the signal could be detected in the cytoplasm of migrating presumptive primordial germ cells (pPGCs) until stage 35. At stage 40, when the cells cease to migrate and reach the dorsal mesentery, the signal disappeared. A possible role of XGRIP2 in pPGCs of Xenopus will be discussed.

The bHLH transcription factor Tcf12 (ME1) mRNA is abundantly expressed in Paneth cells of mouse intestine

Using a large-scale in situ hybridization screening system, we found that mRNA coding for ME1, a basic helix-loop-helix (bHLH) transcription factor, was abundantly expressed in Paneth cells of adult small intestinal crypts. Other functionally related E-protein mRNAs, ME2, and E2A, however, could not be detected in the cells. ME1 mRNA was first detected in the jejunum and ileum two weeks after birth when the number of Paneth cells starts to increase. ME1 is the first identified bHLH transcription factor expressed in the Paneth cells and may be used as a molecular marker and a key molecule for analyzing transcriptional regulation in the Paneth cell.

The future of antisense oligonucleotides in the treatment of respiratory diseases

Antisense oligonucleotides (ASO) are short synthetic DNA molecules designed to inhibit translation of a targeted gene to protein via interaction with messenger RNA. More recently, small interfering (si)RNA have been developed as potent tools to specifically inhibit gene expression. ASO directed against signaling molecules, cytokine receptors, and transcription factors involved in allergic immune and inflammatory responses, have been applied in experimental models of asthma and demonstrate potential as therapeutics. Several ASO-based drugs directed against oncogenes have been developed for therapy of lung cancer, and some have recently reached clinical trials. ASO and siRNA to respiratory syncytial virus infection have demonstrated good potential to treat this condition, particularly in combination with an antiviral drug. Although ASO-based therapeutics are promising for lung diseases, issues of specificity, identification of correct molecular targets, delivery and carrier systems, as well as potential adverse effects must be carefully evaluated before clinical application.

Both cleavage products of the mCLCA3 protein are secreted soluble proteins

Members of the chloride channels, calcium-activated (CLCA) family of proteins and in particular the murine mCLCA3 (alias gob-5) and its human ortholog hCLCA1 have been identified as clinically relevant molecules in diseases with secretory dysfunctions including asthma and cystic fibrosis. Initial studies have indicated that these proteins evoke a calcium-activated chloride conductance when transfected into human embryonic kidney cells 293 cells. However, it is not yet clear whether the CLCA proteins form chloride channels per se or function as mediators of other, yet unknown chloride channels. Here, we present a systematic biochemical analysis of the posttranslational processing and intracellular trafficking of the mCLCA3 protein. Pulse-chase experiments after metabolic protein labeling of mCLCA3-transfected COS-1 or human embryonic kidney 293 cells revealed cleavage of a primary 110-kDa mCLCA3 translation product in the endoplasmic reticulum into a 75-kDa amino-terminal and a 35-kDa carboxyl-terminal protein that were glycosylated and remained physically associated with each other. Confocal fluorescent analyses identified both cleavage products in vesicles of the secretory pathway. Neither cleavage product was associated with the cell membrane at any time. Instead, both subunits were fully secreted into the extracellular environment as a soluble complex of two glycoproteins. These results suggest that the two mCLCA3 cleavage products cannot form an anion channel on their own but may instead act as extracellular signaling molecules. Furthermore, our results point toward significant structural differences between mCLCA3 and its human ortholog, hCLCA1, which is thought to be a single, non-integral membrane protein.

The putative chloride channel hCLCA2 has a single C-terminal transmembrane segment

Calcium-activated chloride channel (CLCA) proteins were first described as a family of plasma membrane Cl(-) channels that could be activated by calcium. Genetic and electrophysiological studies have supported this view. The human CLCA2 protein is expressed as a 943-amino-acid precursor whose N-terminal signal sequence is removed followed by internal cleavage near amino acid position 680. Earlier investigations of transmembrane geometry suggested five membrane passes. However, analysis by the more recently derived simple modular architecture research tool algorithm predicts that a C-terminal 22-amino-acid hydrophobic segment comprises the only transmembrane pass. To resolve this question, we raised an antibody against hCLCA2 and investigated the synthesis, localization, maturation, and topology of the protein. Cell surface biotinylation and endoglycosidase H analysis revealed a 128-kDa precursor confined to the endoplasmic reticulum and a maturely glycosylated 141-kDa precursor at the cell surface by 48 h post-transfection. By 72 h, 109-kDa N-terminal and 35-kDa C-terminal cleavage products were detected at the cell surface but not in the endoplasmic reticulum. Surprisingly, however, the 109-kDa product was spontaneously shed into the medium or removed by acid washes, whereas the precursor and 35-kDa product were retained by the membrane. Two other CLCA family members, bCLCA2 and hCLCA1, also demonstrated preferential release of the N-terminal product. Transfer of the hCLCA2 C-terminal hydrophobic segment to a secreted form of green fluorescent protein was sufficient to target that protein to the plasma membrane. Together, these data indicate that hCLCA2 is mostly extracellular with only a single transmembrane segment followed by a short cytoplasmic tail and is itself unlikely to form a channel.

Differential expression of genes related to HFE and iron status in mouse duodenal epithelium

Iron absorption, distribution, use, and storage are thought to be tightly regulated since altered iron stores may lead to cellular damage and disease. HFE, the hereditary hemochromatosis gene product, is expressed in the crypts of the duodenum, but the molecular mechanism by which it contributes to the inhibition of iron absorption is still unknown. In this study we aimed to identify transcriptional profiles in the duodenal epithelium of Hfe(-/-) mice. We used dedicated microarrays to compare gene expression among the duodenum of Hfe(-/-) mice, induced iron overload mice, and control mice. We found 151 differentially expressed genes and unknown sequences between Hfe(-/-) mice and normal littermates. Gene profiling revealed a gene subset more specific for Hfe inactivation. The functional annotation of upregulated genes highlighted that mucus production and cell maintenance may account for the influence of Hfe on epithelium integrity and luminal iron uptake.

Structure and function of CLCA proteins

CLCA proteins were discovered in bovine trachea and named for a calcium-dependent chloride conductance found in trachea and in other secretory epithelial tissues. At least four closely located gene loci in the mouse and the human code for independent isoforms of CLCA proteins. Full-length CLCA proteins have an unprocessed mass ratio of approximately 100 kDa. Three of the four human loci code for the synthesis of membrane-associated proteins. CLCA proteins affect chloride conductance, epithelial secretion, cell-cell adhesion, apoptosis, cell cycle control, mucus production in asthma, and blood pressure. There is a structural and probable functional divergence between CLCA isoforms containing or not containing beta4-integrin binding domains. Cell cycle control and tumor metastasis are affected by isoforms with the binding domains. These isoforms are expressed prominently in smooth muscle, in some endothelial cells, in the central nervous system, and also in secretory epithelial cells. The isoform with disrupted beta4-integrin binding (hCLCA1, pCLCA1, mCLCA3) alters epithelial mucus secretion and ion transport processes. It is preferentially expressed in secretory epithelial tissues including trachea and small intestine. Chloride conductance is affected by the expression of several CLCA proteins. However, the dependence of the resulting electrical signature on the expression system rather than the CLCA protein suggests that these proteins are not independent Ca2+-dependent chloride channels, but may contribute to the activity of chloride channels formed by, or in conjunction with, other proteins.

Association of the hCLCA1 gene with childhood and adult asthma

Asthma is caused by bronchial inflammation. This inflammation involves mucus overproduction and hypersecretion. Recently, a mouse model of asthma showed that gob-5 is involved in the pathogenesis of asthma. The gob-5 gene is involved in mucus secretion and its expression is upregulated upon antigen attack in sensitized mice. The observation suggests that human homologue of gob-5, hCLCA1 (human calcium-dependent chloride channel-1), may be involved in human disease. We screened for single-nucleotide polymorphisms (SNPs) in hCLCA1 in the Japanese population. We identified eight SNPs, and performed association studies using 384 child patients with asthma, 480 adult patients with asthma, and 672 controls. In haplotype analysis, we found a different haplotype distribution pattern between controls and childhood asthma (P<0.0001) and between controls and adult asthma (P=0.0031). We identified a high-risk haplotype (CATCAAGT haplotype; P=0.0014) and a low-risk haplotype (TGCCAAGT haplotype; P=0.00010) in cases of childhood asthma. In diplotype analysis, patients who had the CATCAAGT haplotype showed a higher risk for childhood asthma than those who did not (P=0.0011). Individuals who had the TGCCAAGT haplotype showed a lower risk for childhood asthma than those who did not (P<0.0001). Our data suggested that variation of the hCLCA1 gene affects patients' susceptibility for asthma.

Respiratory syncytial virus in allergic lung inflammation increases Muc5ac and gob-5

Respiratory syncytial virus (RSV) is associated with wheezing and childhood asthma. We previously reported that RSV infection prolongs methacholine-induced airway hyperresponsiveness in ovalbumin (OVA)-sensitized mice. In addition, allergically sensitized RSV-infected (OVA/RSV) mice had more abundant airway epithelial mucus production compared with OVA mice 14 days after infection, whereas there was almost no mucus in mice that were only RSV infected. We hypothesized that this increased mucus was associated with mucosal expression of Muc5ac, a mucus gene expression in airways, and gob-5, a member of the Ca(2)(+)-activated chloride channel family. By histochemical analysis, we found that there was significantly increased staining for gob-5 and Muc5ac in the airways of OVA/RSV mice compared with either OVA mice or allergically sensitized mice that were challenged with inactivated RSV, and virtually no detectable staining in the RSV group. These findings were confirmed by Western blot analysis. The increased mucus expression in the OVA/RSV group was associated with increased lung levels of interleukin-17, a factor known to stimulate airway mucin gene expression. The impact of virus infection combined with allergic inflammation on mucus production may partially explain the more severe disease and airway hyperresponsiveness associated with RSV in the setting of atopy.

Relationship between a HCO3- -permeable conductance and a CLCA protein from rat pancreatic zymogen granules

Ca(2+)-induced enzyme secretion in the exocrine pancreas is not completely understood. We have proposed that Ca(2+)-induced enzyme secretion in the exocrine pancreas involves activation of ion conductances in the membrane of zymogen granules (ZG). Here we have identified a Ca(2+)-activated anion conductance in rat pancreatic ZG membranes (ZGM). Ca(2+) (2.5-50 microM) increased the conductance for I(-), NO(3)(-), Br(-), or HCO(3)(-), but not for Cl(-), as determined by the rate of valinomycin-induced osmotic lysis of ZG suspended in isotonic K(+)-salts. 4,4'-Diisothiocyanatodihydrostilbene-2,2'-disulfonate (100 microM) or 25 microM dithiothreitol strongly inhibited Ca(2+)-dependent lysis. The permeability sequence, Ca(2+) dependence, and inhibitor sensitivity of ZG anion conductance are reminiscent of a family of epithelial Ca(2+)-activated anion channels (CLCA). CLCA expression was confirmed by RT-PCR with rat pancreatic mRNA and mouse CLCA1 primers. A PCR product (580bp) exhibited 81%, 77%, and 57% amino acid similarity to the three mouse isoforms mCLCA-1, -2, and -3 (mgob-5), respectively. Antibodies against bovine tracheal CLCA1 showed CLCA expression in ZGM by immunoblotting, immunoperoxidase light microscopy, and immunogold labeling. These findings suggest that a CLCA-related protein could account for the Ca(2+)-activated HCO(3)(-) conductance of rat pancreatic ZGM and contribute to hormone-stimulated enzyme secretion.

The murine mCLCA3 (alias gob-5) protein is located in the mucin granule membranes of intestinal, respiratory, and uterine goblet cells

The putative anion channel mCLCA3 (alias gob-5) is the third murine member of the recently discovered family of calcium-activated chloride channels (CLCA family). Preliminary data suggest that mCLCA3 may play a significant role in diseases with secretory dysfunctions, including asthma and cystic fibrosis. In this study, the mCLCA3 protein was characterized biochemically and its cellular and subcellular distribution pattern was established in normal murine tissues. Polyclonal rabbit antibodies were generated and affinity-immunopurified using synthetic oligopeptides corresponding to the extracellular amino terminus of the mCLCA3 polypeptide. After in vitro translation and glycosylation, proteinase K protection assay, and heterologous expression in COS-7 or HEK 293 cells, SDS-PAGE and immunoblotting revealed a protein structure similar to that of previously characterized CLCA proteins. A systematic light, confocal laser scanning, and transmission electron microscopic immunolocalization study, including virtually all murine tissues, identified the mCLCA3 protein exclusively associated with mucin granule membranes of gastrointestinal, respiratory, and uterine goblet cells and other mucin-producing cells. The results suggest that mCLCA3 may be involved in the synthesis, condensation, or secretion of mucins.

Molecular and functional characterization of a murine calcium-activated chloride channel expressed in smooth muscle

To identify the gene products responsible for the calcium-activated chloride current in smooth muscle, reverse transcription-PCR with degenerate primers was performed on mouse intestine and other organs. A new member of the CLCA gene family was identified, mCLCA4, that is expressed preferentially in organs containing a high percentage of smooth muscle cells, including intestine, stomach, uterus, bladder, and aorta. Reverse transcription-PCR using template RNA prepared from mouse bladder and stomach smooth muscle layers dissected free of mucosa yielded mCLCA4-specific bands. In situ hybridization with an mCLCA4-specific probe confirmed prominent expression in smooth muscle of major vessels of the heart but not cardiac muscle. High expression was also detected in the gastrointestinal tract, in bronchioles, and in aortic and lung endothelial cells. Transient expression of mCLCA4 in 293T cells resulted in the appearance of a prominent calcium-activated chloride current. Whole-cell currents activated by ionomycin or methacholine were anion-selective and showed minimal rectification or voltage-dependent gating. Similar to endogenous currents in smooth muscle cells, methacholine-induced currents were transient, and spontaneous transient inward currents were occasionally observed at resting membrane potentials. These results link calcium-activated chloride channels in smooth muscle with a gene family whose members have been implicated in cystic fibrosis, cancer, and asthma.

Molecular structure and physiological function of chloride channels

Cl- channels reside both in the plasma membrane and in intracellular organelles. Their functions range from ion homeostasis to cell volume regulation, transepithelial transport, and regulation of electrical excitability. Their physiological roles are impressively illustrated by various inherited diseases and knock-out mouse models. Thus the loss of distinct Cl- channels leads to an impairment of transepithelial transport in cystic fibrosis and Bartter's syndrome, to increased muscle excitability in myotonia congenita, to reduced endosomal acidification and impaired endocytosis in Dent's disease, and to impaired extracellular acidification by osteoclasts and osteopetrosis. The disruption of several Cl- channels in mice results in blindness. Several classes of Cl- channels have not yet been identified at the molecular level. Three molecularly distinct Cl- channel families (CLC, CFTR, and ligand-gated GABA and glycine receptors) are well established. Mutagenesis and functional studies have yielded considerable insights into their structure and function. Recently, the detailed structure of bacterial CLC proteins was determined by X-ray analysis of three-dimensional crystals. Nonetheless, they are less well understood than cation channels and show remarkably different biophysical and structural properties. Other gene families (CLIC or CLCA) were also reported to encode Cl- channels but are less well characterized. This review focuses on molecularly identified Cl- channels and their physiological roles.

Comparison of the properties of CLCA1 generated currents and I(Cl(Ca)) in murine portal vein smooth muscle cells

Calcium-activated chloride currents (I(Cl(Ca))) have been recorded in various smooth muscle cells but, to date, there has been no information as to the molecular nature of the channel underlying this conductance. We have characterised native I(Cl(Ca)) in freshly dispersed smooth muscle cells isolated from murine portal vein using whole-cell voltage clamp. I(Cl(Ca)) exhibited time-dependent activation at depolarised potentials and rapid deactivation upon repolarisation. The reversal potential of I(Cl(Ca)) was close to the theoretical equilibrium potential (E(Cl)) and was shifted by replacement of external Cl- by SCN- or isethionate. Dithiothreitol (DTT, 1 mM), a blocker of CLCA1, had no effect on the I(Cl(Ca)) current in myocytes. RT-PCR demonstrated the expression of mCLCA1 transcripts, but not mCLCA3 transcripts, in various murine smooth muscle cells including portal vein, as well as cardiomyocytes, and the levels of mCLCA1 transcriptional expression were quantified by real time quantitative RT-PCR. Stable transfection of HEK293 cells with the cDNA encoding mCLCA1 cloned from murine portal vein smooth muscle yielded a current with notable differences in Ca2+ sensitivity, channel kinetics and modulation by DTT from the native I(Cl(Ca)). However, there was some similarity in the pore properties and these data suggest that mCLCA1 alone does not comprise the Cl- channel in portal vein smooth muscle cells.

A calcium-activated chloride channel (HCLCA1) is strongly related to IL-9 expression and mucus production in bronchial epithelium of patients with asthma

BACKGROUND

One of the cardinal features of airway remodeling in asthma is mucus gland hyperplasia and mucus overproduction and hypersecretion. Recently, a calcium-activated chloride channel, HCLCA1, was described that is upregulated by IL-9 and thought to regulate the expression of soluble gel-forming mucins, such as MUC5A/C, a critical component of mucus in the airways.

OBJECTIVE

We sought to examine the expression of HCLCA1 in bronchial biopsy specimens of asthmatic subjects compared with those of control subjects and to demonstrate its relationship with IL-9, IL-9 receptor (IL-9R), and markers of mucus production.

METHODS

Bronchial biopsy specimens from asthmatic (n = 9) and control (n = 10) subjects were stained with periodic acid-Schiff to identify mucus glycoconjugates. IL-9- and IL-9R-positive cells were identified with immunocytochemistry, and HCLCA1 expression was detected by means of in situ hybridization with cRNA probes.

RESULTS

We demonstrate significant increases in IL-9 (P <.001) and IL-9R (P <.05) immunoreactivity, as well as increased expression of HCLCA1 mRNA (P <.001), in the epithelium of asthmatic patients compared with that found in control subjects. There was also an increase in the number of mucusproducing cells in biopsy specimens from asthmatic subjects (P <.001). HCLCA1 mRNA was strongly and selectively colocalized with periodic acid-Schiff and IL-9R-positive epithelial cells. In particular, a strong positive correlation was observed between HCLCA1 mRNA expression and IL-9-positive (r = 0.69, P < 0.01) or IL9R-positive (r = 0.79, P <.01) cells.

CONCLUSION

An upregulation of HCLCA1 in the IL-9- responsive mucus-producing epithelium of asthmatic subjects compared with that seen in control subjects supports the hypothesis that this channel may be responsible, in part, for the overproduction of mucus in asthmatic subjects. These preliminary findings suggest the inhibition of HCLCA1 may be an important new therapeutic approach to control mucus overproduction in chronic airway disorders.

Detection of genes expressed in primary colon cancers by in situ hybridisation: overexpression of RACK 1

AIMS

The isolation of various genes that are expressed in a region specific manner is considered useful for research in molecular pathology. In situ hybridisation (ISH) was used in a screening procedure to isolate these genes efficiently, using colon cancer as a model.

METHODS

Suppression subtractive hybridisation (SSH) between colon cancer tissue samples and corresponding non-cancerous tissues was performed. Genes showing high expression in the cancers were selected using macro-DNA array analysis. As a final screening procedure, conventional ISH was performed to isolate genes expressed specifically in colon cancers.

RESULTS

Sixty nine clones were selected by SSH and macro-DNA array analyses. These clones were then analysed by ISH to examine their expression patterns. ISH screening revealed that all the clones screened showed more intense signals in colon cancers than in non-cancerous tissues. Among them, RACK 1, which is a protein kinase C receptor and a homologue of the G protein beta subunit, was expressed intensely in colon cancer cells. RACK 1 expression was evaluated in multiple samples by ISH, and the results confirmed that RACK 1 was universally overexpressed in cells of all 11 colon cancers examined.

CONCLUSIONS

Many genes, including RACK 1, expressed in colon cancer cells can be isolated efficiently by this method, and their precise expression pattern can be evaluated. These results indicate that ISH is an excellent technique for systemic screening of genes expressed in a region specific manner.

Tumor suppression by a proapoptotic calcium-activated chloride channel in mammary epithelium

Little is known of the roles played by ion channels in cancer. Here we describe a pair of closely related calcium-activated chloride channels whose differential regulation in normal, apoptotic, and transformed mouse cells suggests that channel function is proapoptotic and antineoplastic. While mCLCA1 predominates over mCLCA2 under normal physiological conditions, this relationship is reversed by apoptotic stress both in developing mammary gland and in cultured HC11 mammary epithelial cells. Consistent with an apoptosis-promoting role, splicing of mCLCA2 is disrupted in apoptosis-resistant tumor cell lines and in HC11 cells selected for resistance to detachment-induced apoptosis (anoikis). Unexpectedly, mCLCA1 message is also down-regulated in these cells by at least 30-fold. These results suggest that both genes antagonize survival of mammary tumor cells by sensitizing them to anoikis. When MCF7 or HEK293 tumor cells were transfected with plasmids encoding either mCLCA1 or mCLCA2, colony formation was greatly reduced relative to a vector-transfected control, demonstrating that calcium-sensitive chloride channel (CLCA) expression is deleterious to tumor cell survival. Furthermore, mammary epithelial cells overexpressing mCLCA2 had twice the rate of apoptosis of normal cells when subjected to serum starvation and formed multinuclear giants at a high frequency in normal culture, suggesting that mCLCA2 can promote either apoptosis or senescence.

Characterization of a calcium-activated chloride channel as a shared target of Th2 cytokine pathways and its potential involvement in asthma

Interleukin (IL)-9 is a T helper (Th) 2 cytokine recently implicated as an essential factor in determining susceptibility to asthma. Transgenic mice overexpressing IL-9 exhibit many features that are characteristic of human asthma. To better understand the mechanism by which IL-9 mediates the various biologic activities in asthma, we performed suppressive subtraction hybridization with whole lung from IL-9 transgenic and control mice. Here we report the identification of mCLCA3, a calcium-activated chloride channel that was specifically induced in the lung epithelium of IL-9 transgenic mice. Expression of mCLCA3 could also be induced by intratracheal administration of IL-9 or other Th2 cytokines (IL-4, IL-13), but not by interferon-gamma. Moreover, expression of mCLCA3 was induced in the lung of antigen-exposed mice, and this induction could be suppressed by neutralizing IL-9 antibody treatment, indicating IL-9 is both necessary and sufficient to induce mCLCA3 in this experimental model of asthma. Finally, we demonstrate that hCLCA1 is the human counterpart to mCLCA3 and is also induced in vitro in human primary lung cells by Th2 cytokine treatment. Together, these data strongly implicate the involvement of mCLCA3 (in mice) and hCLCA1 (in humans) in the pathogenesis of Th2 cytokine-mediated asthmatic disorders.

Role of gob-5 in mucus overproduction and airway hyperresponsiveness in asthma

Airway hyperresponsiveness (AHR), goblet cell metaplasia, and mucus overproduction are important features of bronchial asthma. To elucidate the molecular mechanisms behind these pulmonary pathologies, we examined for genes preferentially expressed in the lungs of a murine model of allergic asthma by using suppression subtractive hybridization (SSH). We identified a gene called gob-5 that had a selective expression pattern in the airway epithelium with AHR. Here, we show that gob-5, a member of the calcium-activated chloride channel family, is a key molecule in the induction of murine asthma. Intratracheal administration of adenovirus-expressing antisense gob-5 RNA into AHR-model mice efficiently suppressed the asthma phenotype, including AHR and mucus overproduction. In contrast, overexpression of gob-5 in airway epithelia by using an adenoviral vector exacerbated the asthma phenotype. Introduction of either gob-5 or hCLCA1, the human counterpart of gob-5, into the human mucoepidermoid cell line NCI-H292 induced mucus production as well as MUC5AC expression. Our results indicated that gob-5 may play a critical role in murine asthma, and its human counterpart hCLCA1 is therefore a potential target for asthma therapy.

Molecular characteristics and functional diversity of CLCA family members

1. In the present brief review, we describe some of the molecular and functional characteristics of a novel mammalian family of putative Ca2+-activated chloride channels (CLCA). 2. So far, two bovine (bCLC1; bCLCA2 (Lu-ECAM-1)), three mouse (mCLCA1; mCLCA2; mCLCA3) and four human (hCLCA1; hCLCA2; hCLCA3; hCLCA4) CLCA family members have been cloned. Each CLCA exhibits a distinct, often overlapping, tissue expression pattern. 3. With the exception of the truncated secreted hCLCA3, all CLCA proteins are synthesized as an approximately 125 kDa precursor transmembrane glycoprotein that is rapidly cleaved into 90 and 35 kDa subunits. 4. The CLCA proteins expressed on the luminal surface of lung vascular endothelia (bCLCA2; mCLCA1; hCLCA2) serve as adhesion molecules for lung metastatic cancer cells, mediating vascular arrest and lung colonization. 5. Expression of hCLCA2 in normal mammary epithelium is consistently lost in human breast cancer and in all tumorigenic breast cancer cell lines. Re-expression of hCLCA2 in human breast cancer cells abrogates invasiveness of Matrigel (BD Biosciences-Labware, Bedford, MA, USA) in vitro and tumorigenicity in nude mice, implying that hCLCA2 acts as a tumour suppressor in breast cancer.

Cloning a chloride conductance mediator from the apical membrane of porcine ileal enterocytes

Attempts to attribute ileal brush-border chloride conductance to specific proteins were pursued by screening a porcine intestinal cDNA library. A 0.94-kb clone was identified on expression screening with a monoclonal antibody that inhibited enterocyte brush-border chloride conductance. Further screening approaches led to the isolation of a 3.1-kb full-length sequence called pCLCA1, consistent with the identification of a 2.9-kb transcript through Northern analysis. This sequence had significant homology to the CLCA gene family of calcium-regulated chloride channels, especially to hCLCA1. However, a strong A-kinase consensus phosphorylation site in a predicted cytoplasmic loop of the protein was a notable difference from the hCLCA1 gene product. Several porcine exocrine epithelial tissues, including ileum, trachea, and the major salivary glands express pCLCA1 mRNA. In situ hybridization studies localized the expression of pCLCA1 mRNA to the crypt and villus epithelia of porcine ileum, whereas tracheal expression was observed in both surface epithelium and submucosal glands. In situ expression of pCLCA1 in mouse 3T3 cells induces an ionomycin-dependent chloride conductance activity in these cells.

Ca2+-Activated Cl– Channels: A Newly Emerging Anion Transport Family

A new family of Cl– channels widely expressed in epithelia has been identified. These proteins are associated with Ca2+-sensitive conductive Cl– transport when heterologously expressed. This family may underlie the Ca2+-mediated Cl– conductance responsible for rescue of the cystic fibrosis knockout mouse from significant airway disease.