Phosphorylation of STAT-1 serine 727 is prolonged in HLA-B27-expressing human monocytic cells.
A tissue antigen, HLA-B27, is strongly associated with a group of rheumatic diseases called spondyloarthritides. Despite the intensive research, the exact role of HLA-B27 in the pathogenesis of these diseases is still unclear. Here we studied whether HLA-B27 modulates the phosphorylation of signal transducer and activator of transcription 1 (STAT-1) serine 727 residue and the localization of STAT-1 in Salmonella-infected human monocytic cells. In addition, we studied the role of signaling molecule double-stranded RNA activated protein kinase (PKR) in these modulatory effects. U937 human monocytic cell transfectants stably expressing wild type HLA-B27 or mutated HLA-B27 heavy chains with amino acid substitutions in the B pocket were prepared. The PMA-differentiated cells were infected with S. enteritidis. Western blotting was used to detect the phosphorylation of STAT-1, and to visualize the localization of STAT-1 in the cells confocal microscopy was used. Specific inhibitors were employed to study the role of PKR in STAT-1 phosphorylation. We discovered that the phosphorylation of STAT-1 serine 727 is prolonged in cells expressing misfolding forms of HLA-B27 after S. enteritidis infection, whereas in mock cells and in cells expressing mutated, non-misfolding HLA-B27 the phosphorylation of serine 727 is transient. Interestingly, STAT-1 serine 727 phosphorylation is partly dependent on PKR. In addition, more STAT-1 is localized in the nucleus of HLA-B27-expressing cells, even before an external trigger, when compared to mock cells. In conclusion, our results show that the phosphorylation of STAT-1 serine 727 residue is prolonged in HLA-B27-expressing monocyte-macrophage U937 cells after bacterial infection. This is of interest since the phosphorylation of serine 727 on STAT-1 is suggested to contribute to macrophage activation and promote inflammatory responses. Therefore, our results provide a mechanism which explains how the expression of an HLA-B27 molecule can impact the course of Salmonella infection and reactive arthritis.
Department of Medical Microbiology and Immunology, University of Turku, Turku, Finland. marja.ruuska@utu.fi
Marja
M
Ruuska
Anna S
AS
Sahlberg
Kaisa
K
Granfors
Markus A
MA
Penttinen
D021581:Active Transport, Cell Nucleus; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D015870:Gene Expression; D015796:HLA-B27 Antigen / Q000737:chemistry / Q000235:genetics*; D006801:Humans; D009000:Monocytes / Q000166:cytology / Q000378:metabolism* / Q000382:microbiology; D010766:Phosphorylation; D017510:Protein Folding; D050794:STAT1 Transcription Factor / Q000737:chemistry* / Q000378:metabolism*; D012475:Salmonella / Q000502:physiology; D012694:Serine / Q000378:metabolism*; D013997:Time Factors; D019892:eIF-2 Kinase / Q000378:metabolism
D015796:HLA-B27 Antigen; D050794:STAT1 Transcription Factor; D012694:Serine; D019892:eIF-2 Kinase