trachomatis-infected cells in vitro (Rasmussen et al., 1997). Still, the fact that increases in MICA are Adriamycin seen only on infected cells but not on uninfected bystanders in the same culture suggests that soluble mediators are not sufficient for these effects. Chlamydia trachomatis infection mediates MHC class I downregulation
through direct mechanisms involving the degradation of the transcription factor, RFX5, by chlamydia protease-like activity factor (Zhong et al., 2000). We have previously demonstrated that ‘soluble factors’ could also mediate the downregulation of MHC class I (Ibana et al., 2011a). The downregulation of MHC class I by cytokines, including IL-10 (Caspar-Bauguil et al., 2000) and CXCL12 (Wang et al., 2008) has been demonstrated in other check details culture models, supporting our previous observation that MHC class I downregulation occurs indirectly in the bystander-noninfected cells present in C. trachomatis-infected A2EN cells (Ibana et al., 2011a). Cytokine-mediated induction of dendritic cell MICA transcription by IFNα has been reported (Jinushi et al., 2003), but the overall effects of cytokines on MICA expression appear to be quite pleiotropic with varying effects depending on cell
type and environment (reviewed in Champsaur & Lanier, 2010). In the present study, we observed that MICA is upregulated only in infected cells, demonstrating that the mechanisms underlying C. trachomatis-associated changes in MICA differ from those Selleck Rucaparib altering expression of MHC class I and suggesting C. trachomatis infection does not promote the production of soluble MICA-inducing mediators in our culture system. MICA was first described as cell stress-induced protein in the gastrointestinal epithelium (Groh et al., 1996). Increased MICA expression has been observed during both viral (cytomegalovirus) and
bacterial (M. tuberculosis) infections (Groh et al., 2001; Das et al., 2001). Our observation that upregulation of MICA was limited to C. trachomatis-infected cells may indicate that this induction is via infection-derived stress or danger signals that are absent in noninfected bystander cells. Currently, the exact mechanism underlying the induction of MICA expression during viral and bacterial infection is not completely understood. Interestingly, a recent study suggested that human microRNAs can regulate MICA expression, allowing the maintenance of MICA protein expression at a particular threshold while facilitating acute upregulation of MICA during cellular stress (Stern-Ginossar et al., 2008). If C. trachomatis infection induces MICA expression by interfering with the host microRNA-mediated control pathways, this may explain why MICA induction does not occur on uninfected bystander cells. The latter effect would protect the host from unwarranted NK cell activation.