Mitochondrial carbonic anhydrase CA VB: differences in tissue distribution and pattern of evolution from those of CA VA suggest distinct physiological roles

Carbonic anhydrase inhibitors: The inhibition profiles of the human mitochondrial isoforms VA and VB with anions are very different

The first anion inhibition study of the mitochondrial human carbonic anhydrase (hCA, EC 4.2.1.1) isoform hCA VB is reported. Fluoride, chloride, bromide, iodide, cyanate, thiocyanate, cyanide, azide, bicarbonate, carbonate, nitrate, nitrite, hydrogen sulfide, bisulfite, sulfate, sulfamide, sulfamic acid, phenylboronic acid and phenylarsonic acid were compared as inhibitors of the two mitochondrial isozymes hCA VA and hCA VB. These enzymes are involved in biosynthetic reactions leading to fatty acid and Krebs cycle intermediates biosynthesis in addition to acting as catalysts for the interconversion of carbon dioxide and bicarbonate. The anion inhibition profiles of the two isoforms are dramatically different. The best hCA VB inhibitors were cyanate, thiocyanate, cyanide and hydrogensulfide (K(I)s of 80-76 microM) whereas the least effective ones were the halides (K(I)s of 11-72 mM), with the best inhibitor being fluoride and the least effective ones bromide and iodide. Whereas hCA VA is not sensitive to bicarbonate inhibition (K(I) of 82 mM) similarly to the cytosolic isoform hCA II, hCA VB is well inhibited by this anion, with a K(I) of 0.71 mM. Overall, hCA VB is more sensitive to anion inhibitors as compared to hCA VA. Such data support prior suggestions that the two mitochondrial isozymes play different physiological functions.

An analysis of expression patterns of genes encoding proteins with catalytic activities

BACKGROUND

In situ hybridization (ISH) is a powerful method for visualizing gene expression patterns at the organismal level with cellular resolution. When automated, it is capable of determining the expression of a large number of genes.

RESULTS

The expression patterns of 662 genes that encode enzymes were determined by ISH in the mid-gestation mouse embryo, a stage that models the complexity of the adult organism. Forty-five percent of transcripts encoding metabolic enzymes (n = 297) showed a regional expression pattern. A similar percentage was found for the 190 kinases that were also analyzed. Many mRNAs encoding glycolytic and TCA cycle enzymes exhibited a characteristic expression pattern. The annotated expression patterns were deposited on the Genepaint database and are retrievable by user-defined queries including gene name and sites of expression.

CONCLUSION

The 662 expression patterns discussed here comprised gene products with activities associated with catalysis. Preliminary analysis of these data revealed that a significant number of genes encoding housekeeping functions such as biosynthesis and catabolism were expressed regionally, so they could be used as tissue-specific gene markers. We found no difference in tissue specificity between mRNAs encoding housekeeping functions and those encoding components of signal transduction pathways, as exemplified by the kinases.

A systematic quantification of carbonic anhydrase transcripts in the mouse digestive system

BACKGROUND

Carbonic anhydrases (CAs) are physiologically important enzymes which participate in many gastrointestinal processes such as acid and bicarbonate secretion and metabolic pathways including gluconeogenesis and ureagenesis. The genomic data suggests that there are thirteen enzymatically active members of the mammalian CA isozyme family. In the present study, we systematically examined the mRNA expression levels of all known CA isozymes by quantitative real-time PCR in eight tissues of the digestive system of male and female mice.

RESULTS

The CAs expressed in all tissues were Car5b, Car7, and Car15, among which Car5b showed moderate and Car7 and Car15 extremely low expression levels. Car3, Car12, Car13, and Car14 were detected in seven out of eight tissues and Car2 and Car4 were expressed in six tissues. Importantly, Car1, Car3, and Car13 showed very high expression levels in certain tissues as compared to the other CAs, suggesting that these low activity isozymes may also participate in physiological processes other than CA catalysis and high expression levels are required to fulfil their functions in the body.

CONCLUSION

A comprehensive mRNA expression profile of the 13 enzymatically active CAs in the murine gastrointestinal tract was produced in the present study. It contributes to a deeper understanding of the distribution of CA isozymes and their potential roles in the mouse digestive system.

The role of carbonic anhydrases in renal physiology

Carbonic anhydrase (CA) catalyzes the reversible hydration of CO(2). CA is expressed in most segments of the kidney. CAII and CAIV predominate in human and rabbit kidneys; in rodent kidneys, CAXII, and CAXIV are also present. CAIX is expressed by renal cell carcinoma (RCC). Most of these isoforms, except for rodent CAIV, have high turnover rates. CAII is a cytoplasmic enzyme, whereas the others are membrane-associated; CAIV is anchored by glycosylphosphatidylinositol linkage. Membrane polarity is apical for CAXIV, basolateral for CAXII, and apical and basolateral for CAIV. Luminal membrane CAs facilitate the dehydration of carbonic acid (H(2)CO(3)) that is formed when secreted protons combine with filtered bicarbonate. Basolateral CA enhances the efflux of bicarbonate via dehydration of H(2)CO(3). CAII and CAIV can associate with bicarbonate transporters (e.g., AE1, kNBC1, NBC3, and SCL26A6), and proton antiporter, NHE1 in a membrane protein complex called a transport metabolon. CAXII and CAXIV may also be associated with transporters in normal kidney and CAIX in RCCs. The multiplicity of CAs implicates their importance in acid-base and other solute transport along the nephron. For example, CAII on the cytoplasmic face and CAIV on the extracellular surface provide the 'push' and 'pull' for bicarbonate transport by supplying and dissipating substrate respectively.

Characterization of CA XV, a new GPI-anchored form of carbonic anhydrase

The main function of CAs (carbonic anhydrases) is to participate in the regulation of acid-base balance. Although 12 active isoenzymes of this family had already been described, analyses of genomic databases suggested that there still exists another isoenzyme, CA XV. Sequence analyses were performed to identify those species that are likely to have an active form of this enzyme. Eight species had genomic sequences encoding CA XV, in which all the amino acid residues critical for CA activity are present. However, based on the sequence data, it was apparent that CA XV has become a non-processed pseudogene in humans and chimpanzees. RT-PCR (reverse transcriptase PCR) confirmed that humans do not express CA XV. In contrast, RT-PCR and in situ hybridization performed in mice showed positive expression in the kidney, brain and testis. A prediction of the mouse CA XV structure was performed. Phylogenetic analysis showed that mouse CA XV is related to CA IV. Therefore both of these enzymes were expressed in COS-7 cells and studied in parallel experiments. The results showed that CA XV shares several properties with CA IV, i.e. it is a glycosylated glycosylphosphatidylinositol-anchored membrane protein, and it binds CA inhibitor. The catalytic activity of CA XV is low, and the correct formation of disulphide bridges is important for the activity. Both specific and non-specific chaperones increase the production of active enzyme. The results suggest that CA XV is the first member of the alpha-CA gene family that is expressed in several species, but not in humans and chimpanzees.

Mitochondrial associated metabolic proteins are selectively oxidized in A30P alpha-synuclein transgenic mice--a model of familial Parkinson's disease

Parkinson's disease (PD) is the most common neurodegenerative movement disorder and is characterized by the loss of dopaminergic neurons in the substantia nigra compacta. alpha-Synuclein is strongly implicated in the pathophysiology of PD because aggregated alpha-synuclein accumulates in the brains of subjects with PD, mutations in alpha-synuclein cause familial PD, and overexpressing mutant human alpha-synuclein (A30P or A53T) causes degenerative disease in mice or drosophila. The pathophysiology of PD is poorly understood, but increasing evidence implicates mitochondrial dysfunction and oxidative stress. To understand how mutations in alpha-synuclein contribute to the pathophysiology of PD, we undertook a proteomic analysis of transgenic mice overexpressing A30P alpha-synuclein to investigate which proteins are oxidized. We observed more than twofold selective increases in specific carbonyl levels of three metabolic proteins in brains of symptomatic A30P alpha-synuclein mice: carbonic anhydrase 2 (Car2), alpha-enolase (Eno1), and lactate dehydrogenase 2 (Ldh2). Analysis of the activities of these proteins demonstrates decreased functions of these oxidatively modified proteins in brains from the A30P compared to control mice. Our findings suggest that proteins associated with impaired energy metabolism and mitochondria are particularly prone to oxidative stress associated with A30P-mutant alpha-synuclein.

Expression of a novel carbonic anhydrase, CA XIII, in normal and neoplastic colorectal mucosa

Background

Carbonic anhydrase (CA) isozymes may have an important role in cancer development. Some isozymes control pH homeostasis in tumors that appears to modulate the behaviour of cancer cells. CA XIII is the newest member of the CA gene family. It is a cytosolic isozyme which is expressed in a number of normal tissues. The present study was designed to investigate CA XIII expression in prospectively collected colorectal tumor samples.

Methods

Both neoplastic and normal tissue specimens were obtained from the same patients. The analyses were performed using CA XIII-specific antibodies and an immunohistochemical staining method. For comparison, the tissue sections were immunostained for other cytosolic isozymes, CA I and II.

Results

The results indicated that the expression of CA XIII is down-regulated in tumor cells compared to the normal tissue. The lowest signal was detected in carcinoma samples. This pattern of expression was quite parallel for CA I and II.

Conclusion

The down-regulation of cytosolic CA I, II and XIII in colorectal cancer may result from reduced levels of a common transcription factor or loss of closely linked CA1, CA2 and CA13 alleles on chromosome 8. Their possible role as tumor suppressors should be further evaluated.

Carbonic anhydrases in normal gastrointestinal tract and gastrointestinal tumours

Carbonic anhydrases (CAs) catalyse the hydration of CO₂ to bicarbonate at physiological pH. This chemical interconversion is crucial since HCO₃^- is the substrate for several biosynthetic reactions. This review is focused on the distribution and role of CA isoenzymes in both normal and pathological gastrointestinal (GI) tract tissues. It has been known for many years that CAs are widely present in the GI tract and play important roles in several physiological functions such as production of saliva, gastric acid, bile, and pancreatic juice as well as in absorption of salt and water in intestine. New information suggests that these enzymes participate in several processes that were not envisioned earlier. Especially, the recent reports on plasma membrane-bound isoenzymes IX and XII have raised considerable interest since they were reported to participate in cancer invasion and spread. They are induced by tumour hypoxia and may also play a role in von Hippel-Lindau (VHL)-mediated carcinogenesis.

The differential expression of cytosolic carbonic anhydrase in human hepatocellular carcinoma

Cytosolic carbonic anhydrases (CAs), including CAI, CAII and CAIII are present in normal hepatocytes. This study was aimed to investigate the expression status of CAs in hepatocellular carcinomas (HCC) and cholangiocellular carcinoma (CCC) and the role of tumor progression. The activity, protein expression pattern and messenger RNA of cytosolic CA were analyzed by CA activity analysis, immunoblot and RT-PCR in 60 human hepatocellular carcinomas and 10 human cholangiocellular carcinoma surgical specimens. The in situ distribution of CAI, CAII and CAIII in hepatocellular carcinomas tissues were analyzed by immunohistochemistry. The result showed that in each of 60 human hepatocellular carcinomas and 10 cholangiocellular carcinoma, CA activity and protein expression in tumor area was significantly lower than that of paired adjacent normal tissues (P < 0.01), and mRNA expressions in tumor areas were also reduced (P < 0.001). Furthermore, the immunohistochemical studies have further confirmed this reduction of CAI, CAII and CAIII protein expression in tumor areas. There was a statistically significant reduction in the expression of cytosolic CAII in poorly differentiated cancer (P < 0.001). Furthermore, the reduction of CAI, CAII and CAIII in HCC tumor areas was also revealed in this study and this reduction might promote tumor cell motility and contribute to tumor growth and metastasis.

Cell biology of laryngeal epithelial defenses in health and disease: preliminary studies

Esophageal epithelium has intrinsic antireflux defenses, including carbonic anhydrases (CAs I to IV) that appear to be protective against gastric reflux. This study aimed to investigate the expression and distribution of CA isoenzymes in laryngeal epithelium. Laryngeal biopsy specimens collected from the vocal fold and interarytenoid regions were analyzed by Western blotting and immunofluorescence. Carbonic anhydrases I and II were expressed by the majority of samples analyzed. In contrast, CA III was differentially expressed in the interarytenoid samples and was not detected in any vocal fold samples. The expression of CA III was increased in esophagitis as compared to normal esophageal tissue. Carbonic anhydrase I and III isoenzymes were distributed cytoplasmically in the basal and lower prickle cell layers. The laryngeal epithelium expresses some CA isoenzymes and has the potential to protect itself against laryngopharyngeal reflux. Laryngeal tissue may be more sensitive to injury due to reflux damage than the esophageal mucosa because of different responses of CA isoenzymes.

Transmembrane carbonic anhydrase, MN/CA IX, is a potential biomarker for biliary tumours

BACKGROUND/AIMS

Carbonic anhydrase isoenzyme IX (MN/CA IX) is a transmembrane protein with a suggested function in maintaining the acid-base balance and intercellular communication. Previous studies have demonstrated that MN/CA IX is expressed in the basolateral plasma membrane of normal biliary epithelial cells, but not in hepatocytes. This study was designed to examine the expression of MN/CA IX in hepatobiliary neoplasms and to elucidate its value as a marker for biliary differentiation.

METHODS

Fifty-seven hepatobiliary lesions were immunostained for MN/CA IX using biotin-streptavidin complex method. Twenty samples containing normal biliary epithelium and five containing normal liver tissue were used as controls.

RESULTS

In the biliary epithelial tumours, immunostaining for MN/CA IX was mainly localized at the basolateral surface of the epithelial cells, like in normal mucosa. All non-invasive dysplastic lesions and 57% of invasive lesions of gall-bladder expressed MN/CA IX. In liver, 78% of cholangiocellular malignant lesions showed a positive reaction for MN/CA IX, whereas only 33% of hepatocellular carcinomas showed a weak immunoreaction.

CONCLUSIONS

Our results suggest that abnormal expression of MN/CA IX may be linked to malignant transformation of hepatobiliary cells. In addition, it seems to be a promising marker for biliary differentiation in hepatobiliary neoplasms.

Differential expression of cytoplasmic carbonic anhydrases, CA I and II, and membrane-associated isozymes, CA IX and XII, in normal mucosa of large intestine and in colorectal tumors

This study compares the localization of carbonic anhydrase isozymes (CA) I and II and that of IX and XII in normal large intestine and in colorectal tumors. Immunohistochemical studies were performed on 69 colorectal lesions. While the normal mucosa of the large intestine showed high expression for CA I and II, the intensity of the immunostaining for both isozymes decreased in benign lesions and was very weak in malignant tumors. The reciprocal pattern of expression observed for these cytoplasmic isozymes and transmembrane CA IX and XII in intestinal tissue specimens supports the suggestion that CA IX and XII may be functionally involved in tumor progression to malignancy and/or in invasion. By contrast, while CA I and II are prominent in normal colorectal mucosa, where they play a role in regulation of pH homeostasis and water and ion transport, loss of expression of these cytoplasmic isozymes consistently accompanies progression to malignant transformation.

Genomic analysis of differentially expressed genes in liver and biliary epithelial cells of patients with primary biliary cirrhosis

The characterization of differentially expressed genes provides a powerful tool for identifying molecules that may be involved in the pathogenesis of disease. We have used two independent techniques to identify overexpressed transcripts in bile duct cells and in liver from patients with primary biliary cirrhosis (PBC). In the first method, we used suppressive subtractive hybridization to compare mRNA from isolated PBC bile duct epithelial cells (BECs) to normal BECs and identified 71 clones as transcribed at higher levels in PBC-BECs. Amongst these clones, 62/71 had matches in a non-redundant nucleotide database and 9/71 had matches in an EST database. Of the 62 clones, 51/62 include a complexity of genes involved in cell proliferation, signal transduction, transcription regulation, RNA processing, carbohydrate metabolism and hypothetical/unknown proteins; 4/62 were identified as interstitial collagenase and collagenase precursors, 4/62 as ribosomal proteins, 3/62 as mitochondrial DNA. The mitochondrial cDNA sequences included cytochrome c oxidase, Wnt-13, and the pHL gene, a c-myc oncogene containing coxIII sequence. In the second method, we constructed cDNA libraries from three different PBC livers and sequenced a total of 12,324 independent clones. These 12,324 clones underwent virtual subtraction with 2,814,148 independent clones from Incyte LifeSeq libraries. Twenty one sequences were identified as unique to PBC liver. Collectively, these approaches identified a number of genes involved in signalling, RNA processing, mitochondrial function, inflammation, and fibrosis. Interestingly, both Wnt-13 and Notch transcripts are overexpressed in PBC liver. Further studies are needed to focus on the significance of these genes during the natural history of disease.