title: Proteolysis of nuclear proteins by mu-calpain and m-calpain.
abstract: Purified calpains are capable of proteolyzing several high Mr nuclear proteins and solubilizing a histone H1 kinase activity from rat liver nuclei upon exposure to 10(-6) - 10(-5) M Ca2+. Major nuclear substrates displayed apparent molecular masses of 200, 130, 120, and 60 kDa on Coomassie Blue-stained SDS-PAGE gels. The nuclear proteins and the H1 kinase were released from Triton-treated nuclei following incubation with buffer containing 0.5 M NaCl. They therefore appeared to be internal nuclear matrix proteins. The nuclear H1 kinase activity solubilized by incubation with m-calpain was eluted in the void volume of a Bio-Gel A-1.5m column, indicating an apparent mass greater than 1,500 kDa. Treatment of the calpain-solubilized kinase with 0.5 M NaCl dissociated it to a form having an apparent mass of 300 kDa (Stokes radius = 5.6 nm), suggesting that the 300-kDa (Stokes radius = 5.6 nm), nuclei by calpain treatment as a large complex containing other internal matrix proteins. Purified human erythrocyte mu-calpain was capable of proteolyzing the nuclear matrix proteins at 10(-6) M Ca2+. In contrast, human erythrocyte multicatalytic protease complex produced little cleavage of the nuclear proteins. Proteolysis of nuclear proteins by either mu-calpain or m-calpain was inhibited by calpastatin. These experiments suggest a physiologic role for the calpains in the turnover of nuclear proteins.
authors.affiliation: Department of Pharmacology and Therapeutics, Medical College of Ohio, Toledo 43699.
authors.forename: R L
authors.initials: RL
authors.lastname: Mellgren
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000494:pharmacology; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism; D066298:In Vitro Techniques; D008099:Liver; D008970:Molecular Weight; D009097:Multienzyme Complexes / Q000378:metabolism; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism*; D010449:Peptide Mapping; D006656:Protamine Kinase / Q000737:chemistry / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D051381:Rats; D012995:Solubility
chemical_list: D002135:Calcium-Binding Proteins; D009097:Multienzyme Complexes; D009687:Nuclear Proteins; C033668:calpastatin; D006656:Protamine Kinase; D002154:Calpain; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D002118:Calcium