Gene expression profiling in the submandibular gland, stomach, and duodenum of CAVI-deficient mice.

Carbonic anhydrase VI (CAVI) is the only secreted isozyme of the α-carbonic anhydrase family, which catalyzes the reversible reaction [Formula in text]. It appears that CAVI protects teeth and gastrointestinal mucosa by neutralizing excess acidity. However, the evidence for this physiological function is limited, and CAVI may have additional functions that have yet to be discovered. To explore the functions of CAVI more fully, we generated Car6 (-/-) mice and analyzed Car6 (-/-) mutant phenotypes. We also examined transcriptomic responses to CAVI deficiency in the submandibular gland, stomach, and duodenum of Car6 (-/-) mice. Car6 (-/-) mice were viable and fertile and had a normal life span. Histological analyses indicated a greater number of lymphoid follicles in the small intestinal Peyer's patches. A total of 94, 56, and 127 genes were up- or down-regulated in the submandibular gland, stomach, and duodenum of Car6 (-/-) mice, respectively. The functional clustering of differentially expressed genes revealed a number of altered biological processes. In the duodenum, the significantly affected biological pathways included the immune system process and retinol metabolic processes. The response to oxidative stress and brown fat cell differentiation changed remarkably in the submandibular gland. Notably, the submandibular gland, stomach, and duodenum shared one important transcriptional susceptibility pathway: catabolic process. Real-time PCR confirmed an altered expression in 14 of the 16 selected genes. The generation and of Car6 (-/-) mice and examination of the effects of CAVI deficiency on gene transcription have revealed several affected clusters of biological processes, which implicate CAVI in catabolic processes and the immune system response.

VAMP8/endobrevin as a general vesicular SNARE for regulated exocytosis of the exocrine system.

The molecular mechanism governing the regulated secretion of most exocrine tissues remains elusive, although VAMP8/endobrevin has recently been shown to be the major vesicular SNARE (v-SNARE) of zymogen granules of pancreatic exocrine acinar cells. In this article, we have characterized the role of VAMP8 in the entire exocrine system. Immunohistochemical studies showed that VAMP8 is expressed in all examined exocrine tissues such as salivary glands, lacrimal (tear) glands, sweat glands, sebaceous glands, mammary glands, and the prostate. Severe anomalies were observed in the salivary and lacrimal glands of VAMP8-null mice. Mutant salivary glands accumulated amylase and carbonic anhydrase VI. Electron microscopy revealed an accumulation of secretory granules in the acinar cells of mutant parotid and lacrimal glands. Pilocarpine-stimulated secretion of saliva proteins was compromised in the absence of VAMP8. Protein aggregates were observed in mutant lacrimal glands. VAMP8 may interact with syntaxin 4 and SNAP-23. These results suggest that VAMP8 may act as a v-SNARE for regulated secretion of the entire exocrine system.

Structure of human salivary alpha-amylase crystallized in a C-centered monoclinic space group.

Human salivary alpha-amylase (HSA) is a major secretory protein component of saliva and has important biological functions, including the initial digestion of starch. HSA acts as a monomer and mediates the hydrolysis of alpha-1,4-glucosidic linkages in oligosaccharides. To date, all published crystal structures of HSA have been crystallized as monomers in space group P2(1)2(1)2(1). Here, the serendipitous purification, crystallization and ultimate structure determination of a HSA non-crystallographic symmetry (NCS) dimer, while attempting to purify human carbonic anhydrase VI (HCA VI) from saliva using an affinity resin for alpha-class carbonic anhydrases, is presented. On further investigation, it was shown that HSA could only be copurified using the affinity resin in the presence of HCA VI which is glycosylated and not the non-glycosylated HCA II. The identification of the HSA crystals was carried out by peptide mapping and mass spectrometry. HSA was shown to have crystallized as an NCS dimer in space group C2, with unit-cell parameters a = 150.9, b = 72.3, c = 91.3 A, beta = 102.8 degrees. The NCS dimer crystal structure is reported to 3.0 A resolution, with a refined Rcryst of 0.228. The structure is compared with the previously reported P2(1)2(1)2(1) monomer structures and the crystal packing and dimer interface are discussed.

Luteinizing hormone receptor ectodomain splice variant misroutes the full-length receptor into a subcompartment of the endoplasmic reticulum.

The luteinizing hormone receptor (LHR) is a G protein-coupled receptor that is expressed in multiple RNA messenger forms. The common rat ectodomain splice variant is expressed concomitantly with the full-length LHR in tissues and is a truncated transcript corresponding to the partial ectodomain with a unique C-terminal end. Here we demonstrate that the variant alters the behavior of the full-length receptor by misrouting it away from the normal secretory pathway in human embryonic kidney 293 cells. The variant was expressed as two soluble forms of M(r) 52,000 and M(r) 54,000, but although the protein contains a cleavable signal sequence, no secretion to the medium was observed. Only a very small fraction of the protein was able to gain hormone-binding ability, suggesting that it is retained in the endoplasmic reticulum (ER) by its quality control due to misfolding. This was supported by the finding that the variant was found to interact with calnexin and calreticulin and accumulated together with these ER chaperones in a specialized juxtanuclear subcompartment of the ER. Only proteasomal blockade with lactacystin led to accumulation of the variant in the cytosol. Importantly, coexpression of the variant with the full-length LHR resulted in reduction in the number of receptors that were capable of hormone binding and were expressed at the cell surface and in targeting of immature receptors to the juxtanuclear ER subcompartment. Thus, the variant mediated misrouting of the newly synthesized full-length LHRs may provide a way to regulate the number of cell surface receptors.

Inefficient maturation of the rat luteinizing hormone receptor. A putative way to regulate receptor numbers at the cell surface.

Increasing evidence suggests that the folding and maturation of monomeric proteins and assembly of multimeric protein complexes in the endoplasmic reticulum (ER) may be inefficient not only for mutants that carry changes in the primary structure but also for wild type proteins. In the present study, we demonstrate that the rat luteinizing hormone receptor, a G protein-coupled receptor, is one of these proteins that matures inefficiently and appears to be very prone to premature degradation. A substantial portion of the receptors in stably transfected human embryonic kidney 293 cells existed in immature form of M(r) 73,000, containing high mannose-type N-linked glycans. In metabolic pulse-chase studies, only approximately 20% of these receptor precursors were found to gain hormone binding ability and matured to a form of M(r) 90,000, containing bi- and multiantennary sialylated N-linked glycans. The rest had a propensity to form disulfide-bonded complexes with a M(r) 120,000 protein in the ER membrane and were eventually targeted for degradation in proteasomes. The number of membrane-bound receptor precursors increased when proteasomal degradation was inhibited, and no cytosolic receptor forms were detected, suggesting that retrotranslocation of the misfolded/incompletely folded receptors is tightly coupled to proteasomal function. Furthermore, a proteasomal blockade was found to increase the number of receptors that were capable of hormone binding. Thus, these results raise the interesting possibility that luteinizing hormone receptor expression at the cell surface may be controlled at the ER level by regulating the number of newly synthesized proteins that will mature and escape the ER quality control and premature degradation.

Expression of the mature luteinizing hormone receptor in rodent urogenital and adrenal tissues is developmentally regulated at a posttranslational level.

The LH receptor (LHR) is a G protein-coupled receptor involved in the regulation of ovarian and testicular functions. In this study we demonstrate novel and unexpected patterns of receptor expression and regulation in fetal and adult rodent urogenital and adrenal tissues. Two rat LHR promoter fragments (approximately 2 and 4 kb) were shown to direct expression of the lacZ reporter in transgenic mice to gonads, adrenal glands, and kidneys, starting at 14.5 d post coitum, and to genital tubercles, starting at 11.5 d post coitum. These tissues were also found to express the full-length LHR mRNA and protein during rat fetal development, but, importantly, only immature receptors carrying unprocessed N-linked glycans were detected. After birth, the receptor gene activity ceased, except in the gonads, which started to express the mature receptor carrying fully processed N-linked glycans. Surprisingly, both LHR mRNA and mature protein levels were up-regulated substantially in pregnant female adrenal glands and kidneys at a time that coincides with differentiation of fetal urogenital tissues. Taken together, these results indicate that the LHR protein is expressed constitutively in gonadal and nongonadal urogenital tissues as well in adrenal glands, but its final functional maturation at the posttranslational level appears to be developmentally and physiologically regulated.

Expression of von Hippel-Lindau tumor suppressor and tumor-associated carbonic anhydrases IX and XII in normal and neoplastic colorectal mucosa.

AIM: To analyze possible relationships between CA IX/CA XII and pVHL expression in normal and neoplastic colorectal mucosa. METHODS: Immunohistochemical staining of 42 tissue specimens obtained from 17 cancer patients was performed to evaluate the distribution and semi-quantitatively assess the levels of CA IX, CA XII and pVHL. VHL mRNAs from 14 fresh-frozen tumors was amplified by RT-PCR and subjected to sequencing. CA9 and CA12 mRNA levels were analyzed by semi-quantitative RT-PCR in comparison with VEGF as an indicator of hypoxia that uncouples the pVHL control. RESULTS: Tumor tissues were associated with a borderline increase of CA IX staining signal and slight but significant decrease of CA XII immunoreactivity, whereas no association was found for pVHL. Sequence analysis of RT-PCR-amplified VHL mRNAs revealed no deletions/mutations, suggesting that they were VHL-competent. We did not observe any correlation between pVHL and CA IX/CA XII proteins as well as between VEGF and CA9 mRNAs, but the tumor-associated changes in mRNA levels of VEGF and CA12 showed a significant inverse relationship. CONCLUSION: Our results indicate that CA9 and CA12 are regulated by different intratumoral factors and that lack of apparent relationship between the levels of CA IX/CA XII and pVHL cannot be fully assigned to uncoupling of negative regulatory function of pVHL by tumor hypoxia signified by induced VEGF transcription. The interplay between the functional pVHL and CA IX/CA XII in colorectal tumors seems rather complex and is not evident merely at the expression levels.

An alternative use of basic pGEX vectors for producing both N- and C-terminal fusion proteins for production and affinity purification of antibodies.

Glutathione S-transferase (GST) fusion proteins are widely used in protein production for pure immunogens, protein-protein, and DNA-protein interaction studies. Using basic pGEX vectors, foreign DNA is introduced to the C-terminus of the GST gene and the produced fusion proteins are C-terminally orientated. However, because the orientation of foreign polypeptides may have a very important role in the correct folding of the produced polypeptides, N-terminal fusion proteins are needed to express especially the N-terminus of the foreign polypeptide. Here, we introduce a novel use of the basic pGEX vectors for the production of N-terminal fusion proteins. In this procedure, PCR generated DNA fragments were cloned into the N-terminus of the GST gene in a unique EcoNI site located down-stream of the ATG initiation codon. The N-terminal fusion proteins were expressed in high quantities, easily solubilized, and affinity purified using our modification of current purification protocols. We also introduce here a new modification of the affinity purification of antibodies using covalently crosslinked GST and fusion proteins to glutathione-agarose beads. Our procedure was tested successfully for producing antibodies against both N- and C-terminus of the luteinizing hormone/chorionic gonadotropin receptor.

Immunohistochemical demonstration of carbonic anhydrase isoenzyme VI (CA VI) expression in rat lower airways and lung.

Carbonic anhydrase isoenzyme VI (CA VI), which is transported in high concentrations in saliva and milk into the alimentary tract, is an important element of mucosal protection in the upper alimentary tract. Like alimentary tract mucosa, the respiratory tract mucosa is also exposed to heavy microbial, physical, and chemical stress. The protective and renewal-promoting factors present in the surface mucus of the respiratory tract are mainly produced by the seromucous tracheobronchial glands. Here we studied the secretion of CA VI by these glands in adult and developing rats using immunohistochemical techniques. The serous acinar and duct cells of the tracheobronchial glands stained for CA VI. The presence of the enzyme also in the duct content indicates its active secretion into the surface mucus. CA VI was also visible in the secretory cells and at the base of the ciliated cells of the tracheobronchial surface epithelium. Moreover, the Clara cells of the bronchiolar surface epithelium stained for CA VI. These findings are consistent with the hypothesis that CA VI has a mucosa-protective role not only in the gastrointestinal tract but also in the respiratory tract, where CA VI may act as a pivotal pH neutralizer and growth factor.

Identification and structural characterization of the neuronal luteinizing hormone receptor associated with sensory systems.

The luteinizing hormone receptor (LHR) is a G protein-coupled receptor involved in regulation of ovarian and testicular functions. Here we show that the receptor is present also in specific areas of the peripheral and central nervous system and may thus have a broader functional role than has been anticipated. Full-length LHR mRNA and two receptor protein species of M(r) 90,000 and 73,000, representing mature and precursor forms, respectively, were expressed in adult and developing rat nervous tissue, starting at fetal day 14.5. The receptor was capable of ligand binding because it was purified by ligand affinity chromatography, and human chorionic gonadotropin and LH were able to displace (125)I-labeled human chorionic gonadotropin binding to fetal head membranes in a dose-dependent manner. Finally, two 5'-flanking sequences ( approximately 2 and 4 kb) of the rat LHR gene were shown to direct expression of the lacZ reporter to specific areas of the peripheral and central nervous system in fetal and adult transgenic mice, especially to structures associated with sensory, memory, reproductive behavior, and autonomic functions. Importantly, the transgene activity was confined to neurons and colocalized with the cytochrome P450 side chain cleavage enzyme. Taken together, these results indicate that the neuronal LHR is a functional protein, implicating a role in neuronal development and function, possibly by means of regulating synthesis of neurosteroids.

Localization of carbonic anhydrase XII to the basolateral membrane of H+-secreting cells of mouse and rat kidney.

Membrane-associated carbonic anhydrase (CA) has a crucial role in renal HCO(3)(-) absorption. CA activity has been localized to both luminal and basolateral membranes of the tubule epithelial cells. CA XII is a transmembrane isoenzyme that has been demonstrated in the basolateral plasma membrane of human renal, intestinal, and reproductive epithelia. The present study was designed to demonstrate the distribution of CA XII expression in the rodent kidney. A new polyclonal antibody to recombinant mouse CA XII was used in both Western blotting and immunohistochemistry. Western blotting analysis revealed a 40-45-kD polypeptide in CA XII-expressing CHO cells and isolated membranes of mouse and rat kidney. Immunofluorescence staining localized CA XII in the basolateral plasma membranes of S1 and S2 proximal tubule segments. Abundant basolateral staining of CA XII was seen in a subpopulation of cells in both cortical and medullary collecting ducts. Double immunofluorescence staining identified these cells as H(+)-secreting type A intercalated cells. The localization of CA XII in the peritubular space of proximal tubules suggests that it may play a role in renal HCO(3)(-) absorption, whereas the function of CA XII in the type A intercalated cells needs further investigation.

Salivary carbonic anhydrase VI and its relation to salivary flow rate and buffer capacity in pregnant and non-pregnant women.

OBJECTIVE: Previous studies have shown that pregnancy may have unfavourable effects on oral health. The pH and buffer capacity (BC) of paraffin-stimulated saliva, for example, have been found to decrease towards late pregnancy. Salivary carbonic anhydrase VI (CA VI) probably protects the teeth by accelerating the neutralization of hydrogen ions in the enamel pellicle on dental surfaces. Since estrogens and androgens are known to regulate CA expression in some tissues, we studied here whether salivary CA VI concentration shows pregnancy-related changes. DESIGN: Paraffin-stimulated salivary samples were collected from nine pregnant women 1 month before delivery and about 2 months afterwards and assayed for salivary CA VI concentration, BC and flow rate. The enzyme concentration was determined using a specific time-resolved immunofluorometric assay. The control group consisted of 17 healthy non-pregnant women. RESULTS: The results indicated that salivary CA VI levels varied markedly among individuals, but no significant differences in mean concentrations were seen between the samples collected during late pregnancy and postpartum. BC values were lower during pregnancy, however. CONCLUSIONS: Our findings suggest that CA VI secretion is not significantly affected by the hormonal alterations associated with pregnancy, and confirm the earlier reports that CA VI is not involved in the regulation of actual salivary BC.

The expression of carbonic anhydrase II in hematological malignancies.

PURPOSE: Carbonic anhydrases (CAs) are key enzymes that regulate acid-base homeostasis in both normal and pathological conditions. Recent studies have shown that they are functionally involved in the growth and invasion of cancer cells. However, there are only a few publications on CAs in hematological malignancies. EXPERIMENTAL DESIGN: Here we investigated the presence of CA isozymes in six malignant hematopoietic cell lines and malignant blast cells of bone marrow samples collected from patients with acute myeloid leukemia, acute lymphoblastic leukemia, or chronic myelomonocytic leukemia. RESULTS: Because three of the malignant hematopoietic cell lines expressed CA II, we also set out to examine its expression in a series of bone marrow samples. Positive reactions were found in 16 of 26 cases (62%) of acute myeloid leukemia, 11 of 15 cases (73%) of acute lymphoblastic leukemia, and 1 of 2 cases (50%) of chronic myelomonocytic leukemia. CONCLUSIONS: The results indicate that CA II expression is not restricted to only one cell lineage but may result from a genetic aberration that occurs in both myeloid and lymphatic lineages or in their progenitor cell. Because CA II is expressed in most patients with leukemic blast cells, CA inhibitors may prove to be of value as an adjunct to chemotherapy for such cancers.

The plasma membrane carbonic anhydrase in murine hepatocytes identified as isozyme XIV.

BACKGROUND: Biochemical and histochemical studies have both previously indicated plasma membrane-associated carbonic anhydrase (CA) activity in hepatocytes which has been assumed to be CA IV. However, immunohistochemical data did not support this assignment. Recent northern blotting results indicated the presence of mRNA for the most recently discovered membrane-bound CA isozyme, CA XIV, in the liver. The present study was designed to examine whether CA XIV could contribute to the CA activity described in the hepatocytes. METHODS: Tissue samples from mouse liver were subjected to immunohistochemical staining using the antibodies raised against recombinant mouse CA XIV and CA IV. RT-PCR and western blotting were also performed for CA XIV. RESULTS: A strong immunofluorescent signal was observed in the plasma membrane of mouse hepatocytes. Although CA XIV was expressed on both the apical and basolateral surfaces, the staining was more prominent at the apical (canalicular) membrane domain. The expression of CA XIV in the liver was confirmed by RT-PCR and western blotting. CONCLUSIONS: The presence of CA XIV in the hepatocyte plasma membrane places this novel enzyme at a strategic site to control pH regulation and ion transport between the hepatocytes, sinusoids and bile canaliculi.

Carbonic anhydrase XIV: luminal expression suggests key role in renal acidification.

BACKGROUND: Carbonic anhydrase (CA) plays a fundamental role in regulation of systemic acid-base homeostasis by facilitating urinary acidification. Four CA isozymes (CA II, IV, XII, XIV) have been identified in kidney. Until now, luminal CA IV, a GPI-anchored isozyme, was thought to mediate most bicarbonate absorption. Although CA XIV mRNA has been demonstrated in mouse and human kidney, the localization of this newly discovered CA has not been established. METHODS: RT-PCR and Western blot analyses were used to demonstrate CA XIV mRNA and protein in extracts of cortex and medulla of mouse kidney. Polyclonal antibodies against mouse CA XIV were utilized for immunofluorescence to examine the pattern of expression of CA XIV in the nephron of both rat and mouse kidney. RESULTS: Immunofluorescence staining showed abundant expression of CA XIV in apical plasma membranes of the S1 and S2 segments of proximal tubules, and weaker staining in the basolateral membranes. Also, strong staining was seen in the initial portion of the thin descending limb of Henle. These results show that luminal CA XIV is strongly expressed in regions of the rodent nephron that have been thought to be important in urinary acidification. Staining for CA XIV and CA IV in the same sections showed some areas of co-expression, but also some areas where each was expressed without the other. CONCLUSIONS: Luminal CA XIV may account for a substantial fraction of the bicarbonate reabsorption previously attributed to CA IV. If so, CA XIV and CA IV may be functionally redundant.

Expression and localization of the Na+/H+ exchanger isoform NHE3 in the rat efferent ducts.

The efferent ducts reabsorb most of the fluid released with spermatozoa from the testis. This absorptive capacity results in a severalfold increase in sperm concentration in the proximal epididymis and is partly responsible for maintenance of the optimal microenvironment for the sperm maturation. The fluid absorption is coupled to active Na+ transport and is inhibitable by amiloride, both of which suggest a role for a Na+/H+ exchanger (NHE). NHE3 is an apical membrane NHE responsible for sodium absorption in renal proximal tubule and intestinal epithelium. In the present study, we examined the expression of NHE3 messenger RNA (mRNA) and protein in the rat efferent ducts by reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting and the localization of NHE3 by indirect immunofluoresce. RT-PCR indicated the expression of NHE3 mRNA, and Western blotting showed an NHE3 protein in the efferent duct membrane homogenate. By immunofluorescence, NHE3 was localized to the apical membrane of the nonciliated cells in the efferent duct epithelium, which also expressed aquaporin-1 water channel protein. These results suggest that NHE3 potentially plays an important role in the fluid reabsorption in the efferent ducts.

Carbonic anhydrases in the human adrenal gland and its disorders: Immunohistochemical and biochemical studies of the enzymes.

To study the possible roles of carbonic anhydrases (CA) in the human adrenal glands, an immunohistochemical study (using polycloncal antibodies against CA I and II), and a biochemical assay of CA activity (based on the change in pH caused by the hydration of CO2) were performed in normal human adrenal tissue and adrenocortical adenomas. All of 10 normal adrenal glands showed positive staining for CA II in the zona glomerulosa, whereas weak CA I-positive staining was detected in only 5 glands. A biochemical study of 3 normal human adrenal specimens also demonstrated CA activity only in the outer adrenal cortex. Of 26 adrenocortical adenoma specimens ( 15 aldosteronomas, 6 nonfunctioning adenomas, and 5 Cushing's adenomas), CA I and II immunoreactivity was observed in only 3 and 5 aldosteronoma samples, respectively. A biochemical analysis of CA in 5 adenoma specimens (3 aldosteronomas, 2 nonfunctioning adenomas) detected enzymatic activity in 2 aldosteronomas. In all 26 specimens of non-neoplastic attached adrenals of adrenocortical adenomas, CA II immunoreactivity was present in the zona glomerulosa cells. These results indicate that CAs are present in the zona glomerulosa cells of the non-neoplastic human adrenals glands (but not in the majority of adrenocortical adenomas) and that CA II may constitute the major form of the enzyme. Exclusive localization of CA II in the zona glomerulosa cells in human adrenal glands may suggest a possible involvement of CAs in aldosterone biosynthesis or secretion through ion transport, or both. Our data also suggest that CA II can be used as an immunochemical marker for the zona glomerulosa cells in human adrenal glands.