Genetically modified mice have been studied for more than fifteen years as models of cystic fibrosis (CF). The large amount of experimental data generated illuminates the complex multi-organ pathology of CF and raises new questions relevant to human disease. CF mice have also been used to test experimental therapies prior to clinical trials. This review recapitulates the major phenotypic traits of CF mice and highlights important new findings including aberrant alveolar macrophages, bone and cartilage abnormalities and abnormal bioactive lipid metabolism. Novel data are presented on the intestinal and nasal physiology of F508del-CFTR CF mice backcrossed onto different genetic backgrounds. Caveats, and sources of variability including age, gender and animal husbandry, are discussed. Interspecies differences limit comparison of lung pathology in CF mice to the human disease. The recent development of genetically modified pigs and ferrets heralds the application of more advanced animal models to CF research and drug development.

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A BSTR ACTA recently cloned isoform of cGMPdependent protein kinase (cGK), designated type II, was implicated as the mediator of cGMP-provoked intestinal Cl ؊ secretion based on its localization in the apical membrane of enterocytes and on its capacity to activate cystic fibrosis transmembrane conductance regulator (CFTR) Cl ؊ channels. In contrast, the soluble type I cGK was unable to activate CFTR in intact cells, although both cGK I and cGK II could phosphorylate CFTR in vitro. To investigate the molecular basis for the cGK II isotype specificity of CFTR channel gating, we expressed cGK II or cGK I mutants possessing different membrane binding properties by using adenoviral vectors in a CFTR-transfected intestinal cell line, and we examined the ability of cGMP to phosphorylate and activate the Cl ؊ channel. Mutation of the cGK II N-terminal myristoylation site (Gly 2 3 Ala) reduced cGK II membrane binding and severely impaired cGK II activation of CFTR. Conversely, a chimeric protein, in which the N-terminal membraneanchoring domain of cGK II was fused to the N terminus of cGK I␤, acquired the ability to associate with the membrane and activate the CFTR Cl ؊ channel. The potency order of cGK constructs for activation of CFTR (cGK II > membranebound cGK I chimer > > nonmyristoylated cGK II > cGK I␤) correlated with the extent of 32 P incorporation into CFTR observed in parallel measurements. These results strongly support the concept that membrane targeting of cGK is a major determinant of CFTR Cl ؊ channel activation in intact cells.

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The phytoestrogen resveratrol has putative health-promoting effects and is present in several dietary constituents. Resveratrol is metabolized extensively in the gut epithelium, resulting in the formation of hydrophilic glucuronic acid and sulfate conjugates. These polar resveratrol conjugates need specific transporters to cross the cell membrane. We show here that vectorial transport of some of these metabolites is mediated by multidrug resistance protein 3 (MRP3, ABCC3) and/or breast cancer resistance protein (BCRP, ABCG2) located in the basolateral and apical membranes of enterocytes, respectively. In vitro, MRP3 transports resveratrol-glucuronide (Res-3-G). The absence of Mrp3 in mice results in altered disposition of Res-3-G and its parent compound resveratrol, leading to a reduced percentage of resveratrol being excreted via the urine in Mrp3(Ϫ/Ϫ) mice. Circumstantial evidence suggests that circulating resveratrol is formed by deglucuronidating Res-3-G in vivo, providing a possible explanation for the health beneficial effects of resveratrol in vivo, despite its rapid and extensive conjugation. BCRP transports Res-3-G and resveratrol sulfates in vitro, and its absence in mice results in high plasma levels of resveratrol-di-sulfate, a resveratrol metabolite hardly detectable in the plasma of wild-type mice and in an increased disposal of resveratrol via the urine. The profound effects of ATP-binding cassette transporters on the disposal of resveratrol may be representative for the handling of several other polyphenols of dietary origin.

Nucleotide biosynthesis is fundamental to normal cell proliferation as well as to oncogenesis. Tumor suppressor p53, which prevents aberrant cell proliferation, is destabilized through ubiquitylation by MDM2. Ubiquitin-specific protease 7 (USP7) plays a dualistic role in p53 regulation and has been proposed to deubiquitylate either p53 or MDM2. Here, we show that guanosine 5 0 -monophosphate synthase (GMPS) is required for USP7-mediated stabilization of p53. Normally, most GMPS is sequestered in the cytoplasm, separated from nuclear USP7 and p53. In response to genotoxic stress or nucleotide deprivation, GMPS becomes nuclear and facilitates p53 stabilization by promoting its transfer from MDM2 to a GMPS-USP7 deubiquitylation complex. Intriguingly, cytoplasmic sequestration of GMPS requires ubiquitylation by TRIM21, a ubiquitin ligase associated with autoimmune disease. These results implicate a classic nucleotide biosynthetic enzyme and a ubiquitin ligase, better known for its role in autoimmune disease, in p53 control.

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Previous studies have revealed an adenosine 3',5'-cyclic monophosphate (cAMP)-independent activation of cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channels by the tyrosine kinase inhibitor genistein. To further explore its mechanism of action, we have reconstituted genistein activation of CFTR in excised inside-out membrane patches. In the presence or absence of ATP, genistein appeared unable to open silent CFTR Cl- channels. However, on CFTR prephosphorylation by cAMP-dependent protein kinase (cAK), genistein enhanced CFTR activity by twofold, resulting from a prolonged burst duration. Genistein could also hyperactivate partially phosphorylated CFTR in the absence of cAK and therefore is different from 5'-adenylylimidodiphosphate, which required fully phosphorylated CFTR. Phosphatase-resistant thiophosphorylation likewise primed the CFTR Cl- channel for hyperactivation by genistein in the absence of cAK. Replacement of ATP by GTP as a hydrolyzable nucleotide triphosphate for CFTR did not impair the ability of genistein to activate thiophosphorylated CFTR, despite the fact that GTP is a poor substrate for tyrosine kinases. These findings argue against a role of protein phosphatases or tyrosine kinases but suggest a more direct interaction of genistein with CFTR, possibly at the level of the second nucleotide-binding domain.