Structural basis of the recognition of adeno-associated virus by the neurological system-related receptor carbonic anhydrase IV.

Carbonic anhydrase IV (Car4) is a newly identified receptor that allows adeno-associated virus (AAV) 9P31 to cross the blood-brain barrier and achieve efficient infection in the central nervous system (CNS) in mouse models. However, the molecular mechanism by which engineered AAV capsids with 7-mer insertion in the variable region (VR) VIII recognize these novel cellular receptors is unknown. Here we report the cryo-EM structures of AAV9P31 and its complex with Mus musculus Car4 at atomic resolution by utilizing the block-based reconstruction (BBR) method. The structures demonstrated that Car4 binds to the protrusions at 3-fold axes of the capsid. The inserted 7-mer extends into a hydrophobic region near the catalytic center of Car4 to form stable interactions. Mutagenesis studies also identified the key residues in Car4 responsible for the AAV9P31 interaction. These findings provide new insights into the novel receptor recognition mechanism of AAV generated by directed evolution and highlight the application of the BBR method to studying the virus-receptor molecular mechanism.

Necrosis predicts benefit from hypoxia-modifying therapy in patients with high risk bladder cancer enrolled in a phase III randomised trial.

BACKGROUND AND PURPOSE: Addition of carbogen and nicotinamide (hypoxia-modifying agents) to radiotherapy improves the survival of patients with high risk bladder cancer. The study investigated whether histopathological tumour features and putative hypoxia markers predicted benefit from hypoxia modification. MATERIALS AND METHODS: Samples were available from 231 patients with high grade and invasive bladder carcinoma from the BCON phase III trial of radiotherapy (RT) alone or with carbogen and nicotinamide (RT+CON). Histopathological tumour features examined were: necrosis, growth pattern, growing margin, and tumour/stroma ratio. Hypoxia markers carbonic anhydrase-IX and glucose transporter-1 were examined using tissue microarrays. RESULTS: Necrosis was the only independent prognostic indicator (P=0.04). Necrosis also predicted benefit from hypoxia modification. Five-year overall survival was 48% (RT) versus 39% (RT+CON) (P=0.32) in patients without necrosis and 34% (RT) versus 56% (RT+CON) (P=0.004) in patients with necrosis. There was a significant treatment by necrosis strata interaction (P=0.001 adjusted). Necrosis was an independent predictor of benefit from RT+CON versus RT (hazard ratio [HR]: 0.43, 95% CI 0.25-0.73, P=0.002). This trend was not observed when there was no necrosis (HR: 1.64, 95% CI 0.95-2.85, P=0.08). CONCLUSIONS: Necrosis predicts benefit from hypoxia modification in patients with high risk bladder cancer and should be used to select patients; it is simple to identify and easy to incorporate into routine histopathological examination.

Roles of cytosolic and membrane-bound carbonic anhydrase in renal control of acid-base balance in rainbow trout, Oncorhynchus mykiss.

We tested the hypothesis that cytosolic and membrane-associated carbonic anhydrase (CA IV) are involved in renal urinary acidification and bicarbonate reabsorption in rainbow trout. With the use of homological cloning techniques, a 1,137-bp cDNA was assembled that included an open reading frame encoding for a deduced protein of 297 amino acids. Phylogenetic analysis revealed that this protein was likely a CA IV isoform. With the use of this sequence and a previously described trout cytosolic isoform [tCAc (13)], tools were developed to quantify and localize mRNA and protein for the two CA isoforms. Unlike tCAc, which displayed a broad tissue distribution, trout CA IV mRNA (and to a lesser extent protein) was highly and preferentially expressed in the posterior kidney. The results of in situ hybridization, immunocytochemistry, and standard histological procedures demonstrated that CA IV was likely confined to epithelial cells of the proximal tubule with the protein being expressed on both apical and basolateral membranes. The CA IV-containing tubule cells were enriched with Na(+)-K(+)-ATPase. Similar results were obtained for tCAc except that it appeared to be present in both proximal and distal tubules. The levels of mRNA and protein for tCAc increased significantly during respiratory acidosis (hypercapnia). Although tCA IV mRNA was elevated after 24 h of hypercapnia, tCA IV protein levels were unaltered. By using F3500, a membrane-impermeant (yet filtered) inhibitor of CA, in concert with blood and urine analyses, we demonstrated that CA IV (and possibly other membrane-associated CA isoforms) plays a role in urinary acidification and renal bicarbonate reabsorption.