Promoter activity of carbonic anhydrase II regulatory regions in cultured renal proximal tubular cells

Cyclic AMP and alkaline pH downregulate carbonic anhydrase 2 in mouse fibroblasts

BACKGROUND

The hydration of CO2 catalyzed by the ubiquitous carbonic anhydrase 2 (Ca2) is central for bicarbonate transport, bone metabolism and acid-base homeostasis in metazoans. There is evidence that in some tissues Ca2 expression can be acutely induced by cAMP, whereas in other cell types it is unresponsive to cAMP-mediated transcriptional activation.

METHODS

We isolated fibroblasts from wild type and mice lacking the ubiquitous chloride/bicarbonate exchanger (Ae2a,b(-/-) mice). In these cells the regulation of carbonic anhydrase 2 by cAMP was studied.

RESULTS

We show that Ca2 expression is strongly inhibited by chronic incubation with dibutyryl-cAMP, forskolin or alkaline pH in cultured mouse fibroblasts. Furthermore, fibroblasts obtained from anion exchanger 2 deficient (Ae2a,b(-/-)) mice, which display intracellular alkalosis and increased cAMP production, express less than 10% of control Ca2 mRNA and protein. Surprisingly, inhibition of the bicarbonate-sensitive soluble adenylyl cyclase (sAC) was found to reduce CA2 expression instead of increasing it.

CONCLUSIONS

CA2 expression is strongly regulated by intracellular pH and by cAMP, suggesting a role for soluble adenylyl cyclase. Regulation occurs in opposite directions which may be explained by an incoherent feedforward loop consisting of activation by pCREB and repression by ICER.

Molecular cloning and characterization of the 5'-flanking regulatory region of the carbonic anhydrase nacrein gene of the pearl oyster Pinctada fucata and its expression

The carbonic anhydrase nacrein participates in the formation of the nacreous or prismatic layer of Pinctada fucata. We isolated a genomic clone containing the nacrein gene and cloned the 5'-flanking region. Within the 1336 bp 5' flanking region, we identified putative cis-acting elements, including the TATA box (TATAAAA) at -82 bp, and AP1 (-819 bp) and Oct-1 (-1244 bp) binding sites. In addition to the mantle, the nacrein gene is also expressed in the adductor muscle, liver, and foot. These results showed that nacrein not only takes part in the formation of the hard tissue but also might be involved in acid-base balance, ion transport, and maintenance of ionic concentration. In vitro transcription experiments showed that the addition of human c-jun activates transcription from the nacrein promoter. This is the first report of a promoter from a gene that controls the formation of the hard tissue of mollusk shells.

Quantitative cardiovascular magnetic resonance for molecular imaging

Cardiovascular magnetic resonance (CMR) molecular imaging aims to identify and map the expression of important biomarkers on a cellular scale utilizing contrast agents that are specifically targeted to the biochemical signatures of disease and are capable of generating sufficient image contrast. In some cases, the contrast agents may be designed to carry a drug payload or to be sensitive to important physiological factors, such as pH, temperature or oxygenation. In this review, examples will be presented that utilize a number of different molecular imaging quantification techniques, including measuring signal changes, calculating the area of contrast enhancement, mapping relaxation time changes or direct detection of contrast agents through multi-nuclear imaging or spectroscopy. The clinical application of CMR molecular imaging could offer far reaching benefits to patient populations, including early detection of therapeutic response, localizing ruptured atherosclerotic plaques, stratifying patients based on biochemical disease markers, tissue-specific drug delivery, confirmation and quantification of end-organ drug uptake, and noninvasive monitoring of disease recurrence. Eventually, such agents may play a leading role in reducing the human burden of cardiovascular disease, by providing early diagnosis, noninvasive monitoring and effective therapy with reduced side effects.

Timing and expression pattern of carbonic anhydrase II in pancreas

In the search for genetic markers for assessing the role of duct cells in pancreas growth, we examined whether carbonic anhydrase II (CAII) has ductal cell specificity. We determined the distribution and timing of CAII expression in mouse pancreas from embryonic stage to adult. The pancreatic ducts only start expressing CAII at embryonic day (E) 18.5, with increases after birth. Around E15.5, glucagon-positive cells, but not insulin-positive cells, also express CAII, with further increases by adult. CAII expression was restricted to cells within ductal structures and glucagon-positive cells with no colocalization with any insulin-positive cells at any time. In the human pancreas, CAII expression is restricted to the ducts. Furthermore, the activity of a 1.6-kb fragment of the human promoter with Luciferase assays was moderately strong compared with the cytomegalovirus promoter in human pancreatic duct cell line (PANC-1). Thus, we believe that the CAII gene could serve as a useful pancreatic duct cell marker.

Renal and systemic pH imaging by contrast-enhanced MRI

Perturbations of renal and systemic pH accompany diseases of the kidney, such as renal tubular acidosis, and the ability to image tissue pH would be helpful to assess the extent and severity of such conditions. A dual-contrast-agent strategy using two gadolinium agents, the pH-insensitive GdDOTP(5-) and the pH-sensitive GdDOTA-4AmP(5-), has been developed to generate pH maps by MRI. The renal pharmacokinetics of the structurally dissimilar pH-insensitive contrast agents GdDTPA(2-) and GdDOTP(5-) were found to be similar. On that basis, and on the basis of similarity of structure and charge, the renal pharmacokinetics of GdDOTP(5-) and GdDOTA-4AmP(5-) were assumed to be identical. Dynamic T(1)-weighted images of mice were acquired for 1 hr each following boluses of GdDOTP(5-) and GdDOTA-4AmP(5-). The time-varying apparent concentration of GdDOTP(5-) and the time-varying enhancement in longitudinal relaxation rate following GdDOTA-4AmP(5-) were calculated for each pixel and used to compute pH images of the kidneys and surrounding tissues. MRI pH maps of control mice show acidic regions corresponding to the renal papilla, calyx, and ureter. Pretreatment of mice with the carbonic anhydrase inhibitor acetazolamide resulted in systemic metabolic acidosis and accompanying urine alkalinization that was readily detected by this dual-contrast-agent approach.

Activation of human CAII gene promoter by v-Src: existence of Ras-dependent and -independent pathways

Carbonic anhydrase II (CAII) catalyzes the reversible hydration of carbon dioxide and plays key roles in acid base homeostasis in mammals. We found that human CAII gene promoter could be activated in human cells such as HeLa and T47D cells when the CAII promoter-luciferase gene was transfected with v-Src and assayed as a reporter of the promoter activity. Kinase negative mutants of Src, in contrast, showed little activation. The activation was completely suppressed with the introduction of a dominant-negative Ras in T47D cells, while no suppression was observed in HeLa cells. Introduction of various kinds of deletions into the CAII promoter revealed two essential regions responsible for this activation. No activation, however, was observed in activated Fyn-transfected human cells or in v-Src-transfected rodent cells. These findings suggest that Src can modulate the human CAII promoter by exerting its tyrosine kinase activity in certain human cells, and that two types of Src signaling pathways, Ras-dependent and -independent, exist in a cell type dependent manner.