Visit our Expo - Redox and Inflammation signaling 2012

Oxidative Bax activation as the trigger of the stress-induced intrinsic apoptotic pathway
Lina Ghibelli
Dipartimento di Biologia, Universita' di Roma Tor Vergata
Bax translocation is the most upstream event of the intrinsic apoptotic pathway so far
described. Despite the importance of the issue, the mechanisms that push Bax to mitochondria
are still unknown. The intrinsic pathway of apoptosis is mostly triggered by cell damage,
involving gross environmental alterations such as uncontrolled Ca2+ or ROS overload. This
suggests that its activation may be due not to sophisticated interactions (such as those
involved in the receptor-mediated extrinsic apoptotic pathway), but rather to sudden
environmental changes, thus rendering quite difficult to catch the mechanisms involved. The
idea was to check whether Bax may be a protein "sensing" intracellular chemical/physical
alterations, rather that being activated by specific molecular interactions. Bax translocation to
mitochondria is induced by conformational changes that may be caused by Bax
homodimerisation. We show by computer simulation that the 2 cysteine residues of Bax may
form disulfide bridges, producing conformational changes that favour Bax translocation.
Oxidative, non apoptogenic treatments produce an upshift of Bax migration compatible with
homodimerisation that is reverted by reducing agents; this is accompanied by translocation to
mitochondria. Dimers also appear in pure cytosolic fractions of cell lysates treated with
H2O2, showing that Bax dimerisation may take place in the cytosol. Bax dimers-enriched
lysates support Bax translocation to isolated mitochondria much more efficiently than
untreated lysates, indicating that dimerisation may promote Bax translocation. The absence of
apoptosis in our system allows to demonstrate that Bax moves because of oxidations even in
the absence of apoptosis. This provides the first evidence that Bax dimerisation and
translocation respond to oxidative stimuli, suggesting a novel role for Bax as a sensor of
redox imbalance.
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