Carbonic anhydrase IX: Biochemical and crystallographic characterization of a novel antitumor target
ABSTRACT Isoform IX of the zinc enzyme carbonic anhydrase (CA, EC 22.214.171.124), CA IX, is a transmembrane protein involved in solid tumor acidification through the HIF-1alpha activation cascade. CA IX has a very high catalytic activity for the hydration of carbon dioxide to bicarbonate and protons, even at acidic pH values (of around 6.5), typical of solid, hypoxic tumors, which are largely unresponsive to classical chemo- and radiotherapy. Thus, CA IX is used as a marker of tumor hypoxia and as a prognostic factor for many human cancers. CA IX is involved in tumorigenesis through many pathways, such as pH regulation and cell adhesion control. The X-ray structure of the catalytic domain of CA IX has been recently reported, being shown that CA IX has a typical alpha-CA fold. However, the CA IX structure differs significantly from the other CA isozymes when the protein quaternary structure is considered. Thus, two catalytic domains of CA IX associate to form a dimer, which is stabilized by the formation of an intermolecular disulfide bond. The active site clefts and the proteoglycan (PG) domains are located on one face of the dimer, while the C-termini are located on the opposite face to facilitate protein anchoring to the cell membrane. As all mammalian CAs, CA IX is inhibited by several main classes of inhibitors, such as the inorganic anions, the sulfonamides and their bioisosteres (sulfamates, sulfamides, etc.), the phenols, and the coumarins. The mechanism of inhibition with all these classes of compounds is understood at the molecular level, but the sulfonamides and their congeners have important applications. It has been recently shown that both in vitro, in cell cultures, as well as in animals with transplanted tumors, CA IX inhibition with sulfonamides lead to a return of the extracellular pH to more normal values, which leads to a delay in tumor growth. As a consequence, CA IX represents a promising antitumor target for the development of anticancer agents with an alternative mechanism of action.
- SourceAvailable from: Paolo Paoli
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- "CA IX and CAXII are overexpressed in many solid tumors, and are associated with tumor progression and poor prognosis in various human tumors [17,18]. CA IX, in particular, possesses several peculiarities that fit with tumor physiology: a) CA IX is the most strongly overexpressed gene in response to hypoxia , a very common condition in fast growing solid tumors, being under the transcriptional control of HIF1-α; b) CA IX possesses an extracellular catalytic domain acknowledged of a remarkable high catalytic activity , for that reason being one of the most important protein involved in tumoral extracellular acidification; c) CA IX shows an optimal catalytic activity at pH 6.49 , which is a pH value within the range of that of acidic and hypoxic tumors. "
ABSTRACT: Solid tumors are composed of both cancer cells and various types of accessory cells, mainly fibroblasts, that collectively compose the so called tumor-microenvironment. Cancer-associated fibroblasts have been described to actively participate in cancer progression by establishing a cytokine-mediated as well as metabolic crosstalk with cancer cells. In the present paper we show that activated human fibroblasts are able to boost tumor cells proliferation and that this effect is greatly dependent on stromal carbonic anhydrase IX (CA IX) activity. In fact fibroblasts show a strong upregulation of CA IX expression upon activation by cancer cells, while CA IX products, protons and bicarbonate, exert differential effects on cancer cells proliferation. While acidification of extracellular pH, a typical condition of rapidly growing solid tumors, is detrimental for tumor cells proliferation, bicarbonate, through its organication, supplies cancer cells with intermediates useful to sustain their high proliferation rate. Here we propose a new kind of fibroblasts/tumor cells crosstalk within tumor microenvironment, mediated by stromal CA IX products, aimed to favor cancer cells growth, opening new perspectives on CA IX role in tumor microenvironment.Cell Communication and Signaling 10/2013; 11(1):81. DOI:10.1186/1478-811X-11-81 · 4.67 Impact Factor
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- "The recent solution of the structure of the catalytic domain of CAIX  has provided structural confirmation of its observed catalytic activity and has aided in more rational drug design [15-17]. In contrast to other CA isoforms, CAIX is dimeric , is among the most active CA for the CO2 hydration reaction  and contains a proteoglycan (PG)-like domain immediately adjacent to the catalytic domain, the presence of which may allow the enzyme to function most efficiently at more acidic pH values [17, 18]. A single pass transmembrane domain separates the extracellular portion of CAIX from a short, intracellular tail that is involved in regulating its enzymatic activity . "
ABSTRACT: Carbonic anhydrase IX (CAIX) is a hypoxia-inducible enzyme that is overexpressed by cancer cells from many tumor types, and is a component of the pH regulatory system invoked by these cells to combat the deleterious effects of a high rate of glycolytic metabolism. CAIX functions to help produce and maintain an intracellular pH (pHi) favorable for tumor cell growth and survival, while at the same time participating in the generation of an increasingly acidic extracellular space, facilitating tumor cell invasiveness. Pharmacologic interference of CAIX catalytic activity using monoclonal antibodies or CAIX-specific small molecule inhibitors, consequently disrupting pH regulation by cancer cells, has been shown recently to impair primary tumor growth and metastasis. Many of these agents are in preclinical or clinical development and constitute a novel, targeted strategy of cancer therapy.Oncotarget 01/2012; 3(1):84-97. · 6.63 Impact Factor
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- "CAIX is membrane tethered (Figure 2a) and its catalytic domain is extracellular facing. According to a recent crystal structure (Figure 2b), CAIX exists as a dimer (Alterio et al., 2009; De Simone and Supuran, 2010). The protein contains a proteoglycan-like domain and an intracellular carboxy terminal tail that may be involved in cell–cell adhesion and in regulating the catalytic process (Zavada et al., 2000; Svastova et al., 2003; Hulikova et al., 2009). "
ABSTRACT: In this review, we discuss the role of the tumour-associated carbonic anhydrase isoform IX (CAIX) in the context of pH regulation. We summarise recent experimental findings on the effect of CAIX on cell growth and survival, and present a diffusion-reaction model to help in the assessment of CAIX function under physiological conditions. CAIX emerges as an important facilitator of acid diffusion and acid transport, helping to overcome large cell-to-capillary distances that are characteristic of solid tumours. The source of substrate for CAIX catalysis is likely to be CO₂, generated by adequately oxygenated mitochondria or from the titration of metabolic acids with HCO₃⁻ taken up from the extracellular milieu. The relative importance of these pathways will depend on oxygen and metabolite availability, the spatiotemporal patterns of the cell's exposure to hypoxia and on the regulation of metabolism by genes. This is now an important avenue for further investigation. The importance of CAIX in regulating tumour pH highlights the protein as a potential target for cancer therapy.Oncogene 10/2010; 29(50):6509-21. DOI:10.1038/onc.2010.455 · 8.56 Impact Factor