The secreted protease factor CPAF is responsible for degrading pro-apoptotic BH3-only proteins in Chlamydia trachomatis-infected cells

Abstract

Chlamydia trachomatis has evolved a profound anti-apoptotic activity that may aid in chlamydial evasion of host defense. The C. trachomatis anti-apoptotic activity has been correlated with blockade of mitochondrial cytochrome c release, inhibition of Bax and Bak activation, and degradation of BH3-only proteins. This study presents evidence that a chlamydia-secreted protease factor designated CPAF is both necessary and sufficient for degrading the BH3-only proteins. When the C. trachomatis-infected cell cytosolic extracts were fractionated by column chromatography, both the CPAF protein and activity elution peaks overlapped with the BH3-only protein degradation activity peak. Depletion of CPAF with a CPAF-specific antibody removed the BH3-only protein degradation activity from the infected cell cytosolic extracts, whereas depletion with control antibodies failed to do so. Notably, recombinant CPAF expressed in bacteria was able to degrade the BH3-only proteins, whereas CPAF mutants similarly prepared from bacteria failed to do so. Finally, bacterium-expressed CPAF also degraded the human BH3-only protein Pumaalpha purified from bacteria. These results demonstrate that CPAF contributes to the chlamydial anti-apoptotic activity by degrading the pro-apoptotic BH3-only Bcl-2 subfamily members.