Role of PGRP-S/DnaK Complex in Pathogenicity of Fusobacterium nucleatum
Introduction: Fusobacterium nucleatum (Fn) is one of the most prevalent pathogens found in various systemic and oral infections. It has been shown that Fn is able to induce apoptotic cell death and this ability appears to be mediated through the immune cells being aggregated (Jewett 2000, Huynh 2011). The exact mechanism of how Fn aggregates immune cells remains elusive. PGRP-S is a member of Peptidoglycan recognition proteins (PGRPs) on immune cells and an important host innate immunity arm capable of peptidoglycan and allied bacteria recognition. Hsp70 (heat shock-binding protein 70) is a member of the large stress-induced protein family in eukaryotic cells which makes stable complexes with PGRP-S and induces apoptotic cell death. DnaK homologues (prokaryotic Hsp70) has been identified and characterized in Fn with the Hsp70 family.
Objective: In this study, we investigated the function of PGRP-S/DnaK complex in the binding of immune cells (Jurkat T cells) to Fn and its role in cell death induction.
Material and method: Jurkat T cells were co-cultured with Fn (PK1594) with or without antibodies (Abs) to block DnaK and PGRP-S. Flow cytometry and Caspase-Glo3/7 assay were used to evaluate the levels of binding and apoptosis. Nonspecific IgG antibodies were used as controls. ANOVA with post-hoc Tukey's test was used for statistical analysis.
Results: Blockage of the DnaK and PGRP-S by antibody significantly decreased the binding and aggregation between Jurkat T cells and Fn in flow cytometry (J+Fn=64.3±1.5, J+Fn+Abs=18.7±2.9, P<0.05). Apoptosis of Jurkat T cells also decreased significantly in caspase assays (J+Fn=1700±479, J+Fn+Abs=664±161, P<0.05). Furthermore, the addition of PGRP-S and DnaK monoclonal antibodies inhibited the up-regulation of FasL expression when Jurkats were co-cultured with F. nucleatum in Epi-fluorescence observation.
Conclusion: Our results suggested that PGRP-S/DnaK Complex may play a significant role in the aggregation and apoptosis of Jurkat T cell induced by Fusobacterium nucleatum.