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A potential probiotic strain, Lactobacillus kefiranofaciens M1, was previously isolated from kefir grains, which are used to manufacture the traditional fermented drink kefir. The aim of this study was to investigate the effects of Lb. kefiranofaciens M1 on enterohemorrhagic Escherichia coli (EHEC) infection, using mice and intestinal cell models. BALB/c mice were daily administrated with either phosphate buffered saline or Lb. kefiranofaciens M1 at 2×10(8) cfu/mouse per day intragastrically for 7 d. Intragastric challenges with EHEC (2×10(9) cfu/mouse) were conducted on d 0, 4, and 7 after treatment. Administration of Lb. kefiranofaciens M1 was able to prevent EHEC infection-induced symptoms, intestinal damage, renal damage, bacterial translocation, and Shiga toxin penetration. Furthermore, the mucosal EHEC-specific IgA responses were increased after Lb. kefiranofaciens M1 administration in the EHEC-infected mouse system. Additionally, in vitro, Lb. kefiranofaciens M1 was shown to have a protective effect on Caco-2 intestinal epithelial cells and Caco-2 intestinal epithelial cell monolayers; the bacteria limited EHEC-induced cell death and reduced the loss of epithelial integrity. These findings support the potential of Lb. kefiranofaciens M1 treatment as an approach to preventing EHEC infection and its effects.

Backgound: Tristetraprolin (TTP) family proteins contain conserved tandem CCCH zinc-finger binding to AU-rich elements and C-terminal NOT1-binding domain. TTP is phosphorylated extensively in cells and its mRNA destabilization activity is regulated by protein phosphorylation. Methods: We generated an antibody against phospho-Serine 316 located at C-terminal NOT1-binding site and examined TTP phosphorylation in LPS-stimulated RAW264.7 cells. Knockout of TTP in RAW264.7 cells using CRISPR/Cas9 gene editing was created to explore TTP functions. Results: We demonstrated that Ser316 was phosphorylated by p90 ribosomal S6 kinase 1 (RSK1) and p38-activated protein kinase (MK2), and dephosphorylated by Protein Phosphatase 2A (PP2A). Phosphorylation-mimic mutant of S316D resulted in dissociation with CCR4-NOT deadenylase complex through weakening interaction with CNOT1. Furthermore, Ser316 and serines 52 and 178 were independently contributed to CCR4-NOT complex recruitment in the immunoprecipitation assay using phosphor-mimic mutants. In RAW264.7 macrophages, TTP was induced and Ser316 was phosphorylated through RSK1 and MK2 by LPS stimulation. Knockout of TTP resulted in TNFα mRNA increased due to mRNA stabilization. Overexpression of non-phosphorylated S316A TTP mutant can restore TTP activity and lead to TNFα mRNA decreased. GST pull-down and RNA pull-down analyses demonstrated that endogenous TTP with Ser316 phosphorylation decreased the interaction with CNOT1. Conclusions: Our results suggest that the TTP-mediated mRNA stability is modulated by Ser316 phosphorylation to regulate the TTP interaction with CCR4-NOT deadenylase complex.