title: Interaction between calpain-1 and HSP90: new insights into the regulation of localization and activity of the protease.
abstract: Here we demonstrate that heat shock protein 90 (HSP90) interacts with calpain-1, but not with calpain-2, and forms a discrete complex in which the protease maintains its catalytic activity, although with a lower affinity for Ca2+. Equilibrium gel distribution experiments show that this complex is composed by an equal number of molecules of each protein partner. Moreover, in resting cells, cytosolic calpain-1 is completely associated with HSP90. Since calpain-1, in association with HSP90, retains its proteolytic activity, and the chaperone is displaced by calpastatin also in the absence of Ca2+, the catalytic cleft of the protease is not involved in this association. Thus, calpain-1 can form two distinct complexes depending on the availability of calpastatin in the cytosol. The occurrence of a complex between HSP90 and calpain-1, in which the protease is still activable, can prevent the complete inhibition of the protease even in the presence of high calpastatin levels. We also demonstrate that in basal cell conditions HSP90 and calpain-1, but not calpain-2, are inserted in the multi-protein N-Methyl-D-Aspartate receptor (NMDAR) complex. The amount of calpain-1 at the NMDAR cluster is not modified in conditions of increased [Ca2+]i, and this resident protease is involved in the processing of NMDAR components. Finally, the amount of calpain-1 associated with NMDAR cluster is independent from Ca2+-mediated translocation. Our findings show that HSP90 plays an important role in maintaining a given and proper amount of calpain-1 at the functional sites.
authors.affiliation: Department of Experimental Medicine (DIMES)-Biochemistry Section, and Center of Excellence for Biomedical Research (CEBR), University of Genoa, Viale Benedetto XV, 1-16132 Genoa, Italy.
authors.forename: Monica
authors.initials: M
authors.lastname: Averna
authors.affiliation: Department of Experimental Medicine (DIMES)-Biochemistry Section, and Center of Excellence for Biomedical Research (CEBR), University of Genoa, Viale Benedetto XV, 1-16132 Genoa, Italy.
authors.forename: Roberta
authors.initials: R
authors.lastname: De Tullio
authors.affiliation: Department of Experimental Medicine (DIMES)-Biochemistry Section, and Center of Excellence for Biomedical Research (CEBR), University of Genoa, Viale Benedetto XV, 1-16132 Genoa, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Pedrazzi
authors.affiliation: Department of Experimental Medicine (DIMES)-Biochemistry Section, and Center of Excellence for Biomedical Research (CEBR), University of Genoa, Viale Benedetto XV, 1-16132 Genoa, Italy.
authors.forename: Margherita
authors.initials: M
authors.lastname: Bavestrello
authors.affiliation: Department of Experimental Medicine (DIMES)-Biochemistry Section, and Center of Excellence for Biomedical Research (CEBR), University of Genoa, Viale Benedetto XV, 1-16132 Genoa, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Pellegrini
authors.affiliation: Department of Experimental Medicine (DIMES)-Biochemistry Section, and Center of Excellence for Biomedical Research (CEBR), University of Genoa, Viale Benedetto XV, 1-16132 Genoa, Italy.
authors.forename: Franca
authors.initials: F
authors.lastname: Salamino
authors.affiliation: Department of Experimental Medicine (DIMES)-Biochemistry Section, and Center of Excellence for Biomedical Research (CEBR), University of Genoa, Viale Benedetto XV, 1-16132 Genoa, Italy.
authors.forename: Sandro
authors.initials: S
authors.lastname: Pontremoli
authors.affiliation: Department of Experimental Medicine (DIMES)-Biochemistry Section, and Center of Excellence for Biomedical Research (CEBR), University of Genoa, Viale Benedetto XV, 1-16132 Genoa, Italy.
authors.forename: Edon
authors.initials: E
authors.lastname: Melloni
mesh_terms: D000818:Animals; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002154:Calpain / Q000737:chemistry / Q000378:metabolism*; D002460:Cell Line; D018841:HSP90 Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D007477:Ions / Q000737:chemistry; D008297:Male; D051379:Mice; D018613:Microscopy, Confocal; D010447:Peptide Hydrolases / Q000378:metabolism; D011485:Protein Binding; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics
chemical_list: D002135:Calcium-Binding Proteins; D018841:HSP90 Heat-Shock Proteins; D007477:Ions; D016194:Receptors, N-Methyl-D-Aspartate; D011994:Recombinant Proteins; C033668:calpastatin; D010447:Peptide Hydrolases; D002154:Calpain; D002118:Calcium