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(38) BAX BH3 PEPTIDE INDUCES PERMEABILITY TRANSITION-INDEPENDENT RELEASE OF CYTOCHROME C FROM NEURAL CELL BUT NOT ISOLATED BRAIN OR LIVER MITOCHONDRIA B.M. Polster1,2, K.W.
Kinnally3 and G. Fiskum2
Pro-apoptotic members of the Bcl-2 family, e.g., Bax, can release cytochrome c (CytC) from mitochondria during apoptosis. The BH3 domain of Bax is critical for heterodimerization with other Bcl-2 family proteins and is sufficient for its death-promoting activity. We tested the hypothesis that a Bax peptide containing the BH3 domain can permeabilize the outer mitochondrial membrane and release CytC in the absence of an inner membrane permeability transition (PT). Accordingly, Bax BH3 peptide (10-60 mM) released CytC in the presence of physiological concentrations of ATP and Mg2+ but in the absence of Ca2+ from cortical astrocytes and cerebellar granule neurons and from the mitochondria of GT1-7 and PC12 neural cells. CytC release was accompanied by adenylate kinase release, was not associated with mitochondrial swelling or a significant loss of inner membrane electrical potential, and was unaffected by the PT inhibitor cyclosporin A. As expected, the overexpression of Bcl-2 in the GT1-7 cell line inhibited CytC release. Bax BH3 did not release CytC from rat forebrain or liver mitochondria under the same conditions in which release was induced in cultured cell mitochondria, suggesting the existence of a regulated pathway of CytC release. Overall, results indicate that release of CytC by the Bax BH3 peptide is independent of the mitochondrial PT and support the hypothesis that Bax BH3 is able to modulate outer mitochondrial membrane permeability via a specific regulated pathway. These studies will help elucidate the mechanism of action of BH3-containing proteins and identify their mitochondrial targets. Supported by NS34152 and GM57249.
For further information contact...Carmen Mannella: carmen@wadsworth.org |
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