Human GCIP interacts with CT847, a novel Chlamydia trachomatis type III secretion substrate, and is degraded in a tissue‐culture infection model

Summary The obligate intracellular bacterium Chlamydia trachomatis occupies a parasitophorous vacuole and employs a type III secretion mechanism to translocate host‐interactive proteins. These proteins most likely contribute to pathogenesis through modulation of host cell mechanisms crucial for the establishment and maintenance of a permissive intracellular environment. Using a surrogate Yersinia type III secretion system (T3SS), we have identified the conserved gene product CT847 as a chlamydial T3SS substrate. Yeast two‐hybrid studies using CT847 as bait to screen a HeLa cell cDNA library identified an interaction with mammalian G rap2 c yclin D‐ i nteracting p rotein (GCIP). Immunoblot analyses of C. trachomatis ‐infected HeLa cells showed that GCIP levels begin to decrease (as compared with mock‐infected HeLa cells) between 8 h and 12 h post infection. GCIP was virtually undetectable in 24 h time point material. This decrease was inhibited by proteasome inhibitors lactacystin and MG‐132, and the T3SS inhibitor Compound 1. CT847 was detectible in purified reticulate body but not elementary body lysates, and reverse transcription polymerase chain reaction (RT‐PCR) expression analyses indicate a mid‐cycle expression pattern. Both of these findings are consistent with CT847 contributing to the observed effect on GCIP. Given the established roles of GCIP, we believe that we have discovered a novel C. trachomatis antihost protein whose activity is relevant to chlamydial pathogenesis.