Decreased ras-mitogen-activated protein kinase signaling may cause DNA hypomethylation in T lymphocytes from lupus patients

Abstract

Objective Previous studies have shown that inhibiting T cell DNA methylation causes a lupus‐like disease by modifying gene expression. T cells from patients with lupus exhibit diminished levels of DNA methyltransferase (MTase) enzyme activity, hypomethylated DNA, and changes in gene expression similar to those exhibited by T cells treated with methylation inhibitors, suggesting that DNA hypomethylation may contribute to human lupus. Since it is known that DNA MTase levels are regulated by the ras–mitogen‐activated protein kinase (MAPK) pathway, this study sought to determine whether decreased ras‐MAPK signaling could account for the DNA hypomethylation in lupus T cells. Methods DNA MTase messenger RNA (mRNA) from lupus patients and from healthy controls was quantitated by Northern analysis, and ras‐MAPK signaling was determined by immunoblotting with antibodies to the activated forms of extracellular receptor–associated kinase (ERK). Results were compared with those in T cells in which ras‐MAPK signaling was inhibited with a soluble inhibitor of MAPK ERK 1 (MEK1). Results T cells from patients with active lupus had diminished DNA MTase mRNA levels and decreased signaling through the ras‐MAPK pathway. Inhibiting signaling through the ras‐MAPK pathway with the MEK1 inhibitor decreased DNA MTase mRNA and enzyme activity to the levels seen in lupus T cells, and resulted in DNA hypomethylation resembling that seen in lupus T cells. Conclusion These results suggest that a decrease in signaling through the ras‐MAPK pathway may be responsible for the decreased MTase activity and DNA hypomethylation in patients with lupus.

Defective T-cell ERK signaling induces interferon-regulated gene expression and overexpression of methylation-sensitive genes similar to lupus patients

“…29,35 Inducing a T-cell ERK signaling defect, resulted in reduced expression of Dnmt1, supporting an important role for ERK signaling in regulating Dnmt1 expression. 29 As expected, the expression of T-cell methylation-sensitive genes was increased in the spleen when ERK signaling defect was induced. The overexpression of these methylation-sensitive genes such as CD11a, and CD70 is also observed in patients with active lupus as well as in human T cells treated with DNA methylation inhibitors.…”

“…Indeed, disease activity in lupus patients correlates well with both the degree of T-cell ERK signaling defect as well as the anti-dsDNA antibody titer. 29,35 Inducing a T-cell ERK signaling defect, resulted in reduced expression of Dnmt1, supporting an important role for ERK signaling in regulating Dnmt1 expression. 29 As expected, the expression of T-cell methylation-sensitive genes was increased in the spleen when ERK signaling defect was induced.…”

“…This confirms earlier reports that ERK signaling pathway is involved in regulating Dnmt1 expression. 29 We also measured Dnmt1 expression in vitro in stimulated T cells from dnMEK/CD2-rtTA mice as compared to CD2-rtTA mice treated with doxycycline (2 μg ml −1 ). There was a significant reduction in Dnmt1 mRNA levels in stimulated T cells from dnMEK/CD2-rtTA (0.40 ± 0.05 versus 1.36 ± 0.28 (mean ± s.e.m.…”

“…8,23,28 Lupus T cells display similar decreases in ERK pathway signaling and Dnmt1 levels, and the degree of impairment is directly proportional to disease activity. 29 Also, murine CD4+ T cells treated with hydralazine or the MEK inhibitor U0126 demethylate, overexpress methylation-sensitive T-cell genes and cause anti-DNA antibodies when injected into syngeneic mice. 23 Based on these observations, we hypothesized that acquired ERK pathway signaling defects, occurring in mature T cells, may be fundamental to the development of lupus-like autoimmunity.…”

Genome scan stratified by the presence of anti-double-stranded DNA (dsDNA) autoantibody in pedigrees multiplex for systemic lupus erythematosus (SLE) establishes linkages at 19p13.2 (SLED1) and 18q21.1 (SLED2)

“…23 Interaction of the ras-mitogen-activated protein kinase (MAPK) pathway and the levels of this enzyme also may be altered in patients with lupus. 24 Moreover, in vitro inhibition of this enzyme can induce an immune complex glomerulonephritis with IgG anti-DNA and antihistone antibodies. 25 Calreticulin, a calcium binding multifunctional protein that is a suspected autoantigen that may have a role in transcription regulation 26 and in penetration of antidsDNA into the cells.…”