3. Expression and secretion of cHtrA during chlamydial

infection We further used the specific anti-cHtrA antibodies to characterize the endogenous cHtrA. As shown in Figure 5, cHtrA protein was detected inside the inclusions as early as 12 h after infection and secretion of cHtrA into host cell cytosol became apparent by 24 h post infection. Although CPAF was also detectable at 12 h, the secretion of CPAF was more robust and became very obvious as early as 16 h after infection. The cHtrA protein was detected both within the chlamydial inclusions NSC 683864 and in the host cell cytosol while CPAF mainly accumulated in the host cell cytosol as infection progressed. Although both CPAF and cHtrA are serine proteases Roscovitine secreted by C. trachomatis organisms, their distinct secretion kinetics and intracellular distribution patterns suggest that they may fulfill different functions during chlamydial infection. To further evaluate whether cHtrA secretion is common to all chlamydial organisms, we monitored the cHtrA protein distribution in cells infected with various serovars and strains from different chlamydial species, including 13 C. trachomatis serovars and also isolates representing species of C. muridarum, C. caviae, C. pneumoniae and C. psittaci (Figure 6). The cHtrA

protein was consistently detected in both the lumen of chlamydial inclusion and cytosol of host cells infected with all serovars of C. trachomatis organisms and isolates of C. muridarum, C. caviae and C. pneumoniae but not C. psittaci. Although secretion of cHtrA into the inclusion lumen and further into the cytosol of the infected cells seems to be a common feature of most chlamydial GS-9973 cell line organisms tested, it is not known at this moment why the species C. psittaci, which primarily infect birds, failed to secrete cHtrA into host cytosol. Figure 5 Time course of cHtrA expression C59 cell line during C. trachomatis

infection. The C. trachomatis-infected culture samples were processed at various times after infection (as indicated on the top) for immunofluorescence staining as described in Figure 1 legend. The mouse anti-cHtrA (a to h) and anti-CPAF (mAb 100a; i to p) were visualized with a goat anti-mouse IgG conjugated with Cy3 (red) while the chlamydial organisms were visualized with a rabbit anti-chlamydia antibody plus a goat anti-rabbit IgG-Cy2 conjugate (green). Note that cHtrA was first detected inside the chlamydial inclusions at 12 hours after infection [panel d, yellow (overlapping with organisms) & red (free of chlamydial organisms) arrowheads], similar to the detection of CPAF. However, cHtrA secretion into host cell cytosol was only detected 24 h after infection while secretion of CPAF was already obvious by 16 h post infection. Figure 6 Secretion of cHtrA into host cell cytosol by most chlamydial organisms tested. HeLa cells infected with C. trachomatis serovars A, B, Ba, C, D, E, F, H, I, K, L1, L2, L3, C. muridarum Nigg strain, C. caviae GPIC, C. penumonaie AR39 isolate &C.