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Proteolytic degradation of nitric oxide synthase isoforms by calpain is modulated by the expression levels of HSP90
Author(s) -
Averna Monica,
Stifanese Roberto,
De Tullio Roberta,
Salamino Franca,
Bertuccio Mara,
Pontremoli Sandro,
Melloni Edon
Publication year - 2007
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2007.06133.x
Subject(s) - calpain , hsp90 , proteolysis , nitric oxide synthase , nitric oxide , biochemistry , chemistry , jurkat cells , calpastatin , microbiology and biotechnology , proteases , heat shock protein , nitric oxide synthase type iii , protein degradation , biology , enzyme , enos , immunology , immune system , organic chemistry , t cell , gene
Ca 2+ loading of Jurkat and bovine aorta endothelium cells induces the degradation of the neuronal and endothelial nitric oxide synthases that are selectively expressed in these cell lines. For neuronal nitric oxide synthase, this process involves a conservative limited proteolysis without appreciable loss of catalytic activity. By contrast, endothelial nitic oxide synthase digestion proceeds through a parallel loss of protein and catalytic activity. The chaperone heat shock protein 90 (HSP90) is present in a large amount in Jurkat cells and at significantly lower levels in bovine aorta endothelium cells. The differing ratios of HSP90/nitric oxide synthase (NOS) occurring in the two cell types are responsible for the conservative or nonconservative digestion of NOS isozymes. Consistently, we demonstrate that, in the absence of Ca 2+ , HSP90 forms binary complexes with NOS isozymes or with calpain. When Ca 2+ is present, a ternary complex containing the three proteins is produced. In this associated state, HSP90 and NOS forms are almost completely resistant to calpain digestion, probably due to a structural hindrance and a reduction in the catalytic efficiency of the protease. Thus, the recruitment of calpain in the HSP90–NOS complexes reduces the extent of the proteolysis of these two proteins. We have also observed that calpastatin competes with HSP90 for the binding of calpain in reconstructed systems. Digestion of the proteins present in the complexes can occur only when free active calpain is present in the system. This process can be visualized as a novel mechanism involving the association of NOS with HSP90 and the concomitant recruitment of active calpain in ternary complexes in which the proteolysis of both NOS isozymes and HSP90 is significantly reduced.