Abstract
ObjectiveTo investigate the role of HLA-B27 expression in the regulation of RNA binding protein (RBP) Embryonic Lethal Abnormal Vision (ELAV) L1/Human antigen R (HuR) expression in Salmonella-infected or LPS-stimulated human monocytic cells, since HuR is a critical regulator of the post-transcriptional fate of many genes (e.g. TNFα) important in inflammatory response.MethodsU937 monocytic cells were stably transfected with pSV2neo resistant vector (mock), wild type HLA–B27, or mutated HLA–B27 with amino acid substitutions in the B pocket. Cells were differentiated, infected with Salmonella enteritidis or stimulated with lipopolysaccharide. The expression levels of HuR protein and cleavage products (CP1 and CP2) were detected by Western blotting and flow cytometry. Specific inhibitors were used to study the role of PKR and p38 in HuR expression and generation of CPs. TNFα and IL-10 secretion after p38 and PKR inhibition were measured by ELISA.ResultsFull length HuR is overexpressed and HuR cleavage is disturbed in U937 monocytic cells expressing HLA-B27 heavy chains (HC). Increased full length HuR expression, disturbed cleavage and reduced dependence on PKR after infection correlate with the expression of glutamic acid 45 in the B pocket that is linked to the misfolding of HLA-B27.ConclusionResults show that the expression of HLA-B27 HCs modulates the intracellular environment of U937 monocyte/macrophages by altering HuR regulation. This phenomenon is at least partly dependent on the misfolding feature of the B27 molecule. Since HuR is an important regulator of multiple genes involved in inflammatory response observations offer an explanation how HLA-B27 may modulate inflammatory response.
Highlights
Reactive arthritis (ReA) is a systemic inflammatory disease which belongs to a group of spondyloarthropathies (SpA)
The expression levels of transfected HLA-B27 on U937 cells were close to that physiologically expressed on the cell surface of peripheral blood monocytes [27]
We have previously shown that the expression of HLA-B27 influences on the intracellular environment of the monocytic U937 cells by altering the expression and activity of protein kinase RNA (PKR) and p38dependent signaling [1,2,3]
Summary
Reactive arthritis (ReA) is a systemic inflammatory disease which belongs to a group of spondyloarthropathies (SpA). It is suggested that the expression of HLA-B27, a known risk factor for ReA and all SpAs, modifies the intracellular environment of U937 monocyte/macrophages by altering important cellular signaling pathways [1,2,3]. This is of interest because the diseasetriggering bacteria or bacterial antigens e.g. lipopolysaccharide (LPS) are shown to persist in ReA patients for an abnormally long time [4,5,6,7]. These observations suggest that the interaction between HLA-B27-
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