Abstract
Cryptosporidium is a protozoan parasite that infects the gastrointestinal epithelium and causes a diarrheal disease. Toll-like receptor (TLR)- and NF-κB-mediated immune responses from epithelial cells, such as production of antimicrobial peptides and generation of reactive nitrogen species, are important components of the host's defense against cryptosporidial infection. Here we report data demonstrating a role for miR-27b in the regulation of TLR4/NF-κB-mediated epithelial anti-Cryptosporidium parvum responses. We found that C. parvum infection induced nitric oxide (NO) production in host epithelial cells in a TLR4/NF-κB-dependent manner, with the involvement of the stabilization of inducible NO synthase (iNOS) mRNA. C. parvum infection of epithelial cells activated NF-κB signaling to increase transcription of the miR-27b gene. Meanwhile, downregulation of KH-type splicing regulatory protein (KSRP) was detected in epithelial cells following C. parvum infection. Importantly, miR-27b targeted the 3′-untranslated region of KSRP, resulting in translational suppression. C. parvum infection decreased KSRP expression through upregulating miR-27b. Functional manipulation of KSRP or miR-27b caused reciprocal alterations in iNOS mRNA stability in infected cells. Forced expression of KSRP and inhibition of miR-27b resulted in an increased burden of C. parvum infection. Downregulation of KSRP through upregulating miR-27b was also detected in epithelial cells following LPS stimulation. These data suggest that miR-27b targets KSRP and modulates iNOS mRNA stability following C. parvum infection, a process that may be relevant to the regulation of epithelial anti-microbial defense in general.
Highlights
Cryptosporidium, a zoonotic parasite of the phylum Apicomplexa, is found in 65% to 97% of surface water in the United States
Our study provides a new area of exploration for fine-tuning Toll-like receptor (TLR)/NF-kB-mediated host reactions in response to microbial challenge
We demonstrated that activation of TLR4/NF-kB signaling in epithelial cells regulates transcription of miRNA genes to orchestrate host anti-C. parvum immune responses through modulation of miRNA-mediated posttranscriptional suppression [21,22,23]
Summary
Cryptosporidium, a zoonotic parasite of the phylum Apicomplexa, is found in 65% to 97% of surface water in the United States. This parasite is resistant to standard disinfection applied to drinking water and has been recognized as the leading cause of waterborne disease outbreaks worldwide [1]. C. parvum sporozoites can travel up to infect the epithelial cells lining the biliary tract, mainly in AIDS patients [1,2]. Cryptosporidial infection is usually limited to epithelial cells at the mucosal surface, where the parasite undergoes both intracellular and extracellular life stages; C. parvum is classified as a ‘‘minimally invasive’’ mucosal pathogen [1,2]
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