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Transcriptional Regulation of IL-8 by Staphylococcus aureus in Human Conjunctival Cells Involves Activation of AP-1

¹From the Departments of Surgical Specialties and ²Experimental Pathology and Microbiology, The University of Messina, Messina, Italy.

PURPOSE. To identify signal transduction pathways involved in interleukin (IL)-8 expression by human conjunctival cells challenged with Staphylococcus aureus.

METHODS. Conjunctival cells were cultured in the presence of live or heat-killed S. aureus. IL-8 protein and mRNA were determined by ELISA and RT-PCR, respectively. Activation of mitogen-activated protein kinases (MAPKs) and NF-B was analyzed by Western blot analysis with phosphospecific antibodies. Conjunctival cells were transfected with wild-type (wt) or mutated IL-8 promoters (IL-8-97, lacking the AP-1 site; IL-8-97 mutant C/EBP; IL-8-97 mutant NF-B; IL-8/AP-1 double mutant for C/EBP and NF-B) or c-Jun-NH₂-terminal kinase (JNK)–responsive GAL-c-Jun. In further experiments, cells were cotransfected with wt IL-8 promoter and expression plasmids for p38MAPK-responsive C/EBP homologous protein (CHOP) or wt or dominant negative transactivation domain mutant (TAM-67) c-Jun. A protein–DNA binding study was performed by electrophoretic mobility shift assay (EMSA), to identify the transcription factors bound to the IL-8 promoter.

RESULTS. S. aureus induced significant IL-8 expression and synthesis in human conjunctival epithelial cells by activating c-Jun phosphorylation and transactivation potential via JNK. The IL-8 promoter activation was NF-B- and p38MAPK-independent. Transfection and EMSA experiments suggested that only AP-1 transcription factors were necessary for optimal IL-8 expression.

CONCLUSIONS. Human conjunctival epithelial cells possess the ability to respond to Gram-positive S. aureus and to activate the innate immune response by the IL-8 gene expression. These results are the first to delineate the transcription factors involved in S. aureus–induced IL-8 release by conjunctival epithelium.