title: Role of calpain in the regulation of CFTR (cystic fibrosis transmembrane conductance regulator) turnover.
abstract: The level of the mature native 170 kDa form of CFTR (cystic fibrosis transmembrane conductance regulator) at the plasma membrane is under the control of a selective proteolysis catalysed by calpain. The product of this limited digestion, consisting of discrete fragments still associated by strong interactions, is removed from the plasma membrane and internalized in vesicles and subject to an additional degradation. This process can be monitored by visualizing the accumulation of a 100 kDa fragment in a proliferating human leukaemic T-cell line and in human circulating lymphocytes. In reconstructed systems, and in intact cells, the conversion of native CFTR into the 100 kDa fragment linearly correlated with calpain activation and was prevented by addition of synthetic calpain inhibitors. A reduction in Ca2+ influx, by blocking the NMDA (N-methyl-D-aspartate) receptor Ca2+ channel, inhibited the conversion of the native 170 kDa fragment into the 100 kDa fragment, whereas an endosome acidification blocker promoted accumulation of the digested 100 kDa CFTR form. An important role in calpain-mediated turnover of CFTR is exerted by HSP90 (heat-shock protein 90), which, via association with the protein channel, modulates the degradative effect of calpain through a selective protection. Taken together these results indicate that CFTR turnover is initiated by calpain activation, which is induced by an increased Ca2+ influx and, following internalization of the cleaved channel protein, and completed by the lysosomal proteases. These findings provide new insights into the molecular mechanisms responsible for the defective functions of ion channels in human pathologies.
authors.affiliation: Biochemistry Section, Department of Experimental Medicine, University of Genoa, Viale Benedetto XV, Genoa, Italy.
authors.forename: Monica
authors.initials: M
authors.lastname: Averna
authors.forename: Roberto
authors.initials: R
authors.lastname: Stifanese
authors.forename: Raffaella
authors.initials: R
authors.lastname: Grosso
authors.forename: Marco
authors.initials: M
authors.lastname: Pedrazzi
authors.forename: Roberta
authors.initials: R
authors.lastname: De Tullio
authors.forename: Franca
authors.initials: F
authors.lastname: Salamino
authors.forename: Sandro
authors.initials: S
authors.lastname: Pontremoli
authors.forename: Edon
authors.initials: E
authors.lastname: Melloni
mesh_terms: D000818:Animals; D002154:Calpain / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000378:metabolism*; D018841:HSP90 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D021381:Protein Transport; D051381:Rats
chemical_list: D018841:HSP90 Heat-Shock Proteins; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D002154:Calpain