Infrared radiation affects the mitochondrial pathway of apoptosis in human fibroblasts.

We have previously observed that near-infrared (IR) pre-irradiation protects normal human dermal fibroblasts from ultraviolet (UV) cytotoxicity in vitro. Here, we show that IR pre-irradiation of human fibroblasts inhibited UVB activation of caspase-9 and -3, leading us to study early events in the mitochondrial apoptotic pathway after IR irradiation. IR irradiation led to a partial release of cytochrome c and Smac/Diablo but not apoptosis-inducing factor (AIF). This was accompanied by a slight but transient decrease in the mitochondrial membrane potential (Deltapsim) and by the insertion of Bax into mitochondrial membrane. Early apoptotic events in the mitochondrial pathway thus occurred after IR irradiation despite a lack of caspase-9 and -3 activation. This could be explained by the induction by IR of the expression of heat shock protein Hsp27, which is known to prevent apoptosome assembly. Furthermore, the balance between pro-apoptotic (i.e., Bax) and anti-apoptotic (i.e., Bcl-2 or Bcl-xL) proteins, which was rather pro-apoptotic after IR exposure, became anti-apoptotic 24 h later, suggesting a protective effect. Together, these actions could also contribute to prepare the cell to resist UVB-triggered apoptosis. Finally, isolated rat liver mitochondria-released cytochrome c in response to IR, demonstrating that mitochondria were a primary target of IR radiation.

The expression of a new variant of the pro-apoptotic molecule Bax, Baxpsi, is correlated with an increased survival of glioblastoma multiforme patients.

Pro- and anti-apoptotic members of the BCL-2 family play a central role in the implementation of apoptosis. Bax, a pro-apoptotic member of this family, has as such been considered as a potential tumor suppressor. Here, we have examined the expression of Bax in 55 patients with glioblastoma multiforme (GBM), the most common and aggressive form of brain tumors. We report on the existence of a new form of Bax, present in 24% of the patients, which we called Baxpsi. Baxpsi is a N-terminal truncated form of Bax which results from a partial deletion of the exon 1 of Bax gene. Baxpsi and the wild-type form, Baxalpha, are encoded by distinct mRNAs, both of which are present in normal tissues. Glial tumors express either Baxalpha or Baxpsi proteins, an apparent consequence of an exclusive transcription of the corresponding mRNAs. The latter feature could be partially linked to distinct methylation profiles of Bax gene in these tumors. The Baxpsi protein is preferentially localized to mitochondria and is a more powerful inducer of apoptosis than Baxalpha. Baxpsi tumors exhibit a slow proliferation in Swiss nude mice and this feature can be circumvented by the co-expression of the Bcl-2 transgene, the functional antagonist of Bax. More importantly, the expression of Baxpsi correlates with a longer survival in patients (18 months versus 10 months for Baxalpha patients). Thus, our results provide the first indication of a beneficial involvement of a variant of the pro-apoptotic protein Bax in tumor progression.