An epistatic effect of apaf-1 and caspase-9 on chlamydial infection

Abstract

Chlamydia is an obligate intracellular bacterial pathogen that replicates solely within a membrane-bound vacuole termed an inclusion. Chlamydia seems to perturb multiple cellular processes of the host, such as, rearrangement of the membrane trafficking system for its intracellular multiplication, and inhibition of host cell apoptosis for persistent infection. In an attempt to clarify host factor involvement in apoptosis regulation, we found that inhibition of Caspase-9 restricted, while Apaf-1 promoted, Chlamydia pneumoniae infection in HEp-2, HeLa, and mouse epithelial fibroblast (MEF) cells. These opposition contributions to the chlamydial infection were confirmed using caspase-9−/− and apaf-1−/− MEFs. Similar phenomena also appeared in the case of infection with Chlamydia trachomatis. Interestingly, caspase-9 in apaf-1−/− MEFs was activated by chlamydial infection but during the infection caspase-3 was not activated. That is, caspase-9 was activated without support for multiplication and activation by Apaf-1, and the activated caspase-9 may be physically disconnected from the caspase cascade. This may be partially explained by the observation of caspase-9 accumulation within chlamydial inclusions. The sequestration of caspase-9 by chlamydia seems to result in apoptosis repression, which is crucial for the chlamydial development cycle. Because Apaf-1 shares domains with intracellular innate immune receptor NOD1, it may play a key role in the strategy to regulate chlamydial infection.

Identification of <i>Chlamydia pneumoniae</i> candidate genes that interact with human apoptotic factor caspase-9

“…3a). This supports the previous observation that caspase-9 accumulates in inclusions (Rahman et al, 2015), as well as the finding of the Y2H assay. Further investigation is required to clarify the EB factor(s) involved in the binding of caspase-9 and its significance.…”

“…In our previous study, we found that during C. pneumoniae infection, caspase-9 was sequestered to, and accumulated into, the inclusion and, interestingly, it was activated even under conditions lacking Apaf-1, and caspase-9 activation supported infection by C. pneumoniae (Rahman et al, 2015). It is possible that there might be many paths involved in the control of host apoptosis by chlamydial infection and each Chlamydia species evolutionally alter different paths for their tissue or host tropism.…”

“…C. pneumoniae bition of host cell apoptosis (Gao and Kwaik, 2000). C. pneumoniae has been previously reported to inhibit apoptosis induced by STS and TNF-a (Geng et al, 2000;Rahman et al, 2015).…”

“…GST-Casp9 was purified using Glutathione Sepharose 4B beads (Amersham/GE Healthcare, Marlborough, MA). GST-Casp9 and purified EBs of C. pneumoniae J138 (Rahman et al, 2015) were mixed in lysis buffer and incubated at 37∞C for 15 min. EBs were washed with lysis buffer three times and collected by centrifugation at 4∞C for 5 min at 21,500 ¥ g. GST-Casp9 was then analyzed by western blotting using anti-pro-caspase-9 mouse monoclonal antibody (Santa Cruz, Dallas, TX), followed by a second detection using anti-Chlamydia Pmp mouse monoclonal antibody HITACHI,Tokyo,Japan).…”

Duloxetine Attenuates Paclitaxel-Induced Peripheral Nerve Injury by Inhibiting p53-Related Pathways

“…The Bcl2 family of proteins plays a central role in the apoptosis process. The Bcl2 family includes Bcl2, Bax, Bad, and Bcl-xL (Zheng et al, 2016;Rahman et al, 2015 JPET # 265082 20 inhibit apoptosis. In fact, the ratio of Bax to Bcl2 determines the sensitivity to cell death (Amin et al, 2014).…”