Association of a four–amino acid residue insertion polymorphism of the HS1 gene with systemic lupus erythematosus: Molecular and functional analysis

Abstract

Objective. To investigate whether polymorphism(s) or mutation(s) in the hematopoietic cellspecific Lyn substrate 1 (HS1) gene are involved in the pathogenesis of systemic lupus erythematosus (SLE).Methods. The entire coding region of the HS1 gene was analyzed by reverse transcriptase-polymerase chain reaction/single-strand conformational polymorphism analysis. HS1-transfected WEHI-231 cells or B lymphocytes from patients with SLE were studied for apoptosis, activation, and proliferation by flow cytometric analysis and MTT assay.Results. We identified a glutamic acid-prolineglutamic acid-proline insertion between codons 366 and 367 (EPEP366-367ins) and 2 amino acid substitutions (A235T and E361K). The genotype frequency among individuals homozygous for the EPEP؉ allele was 0.184 in 201 patients with SLE but only 0.098 in 184 healthy individuals (P ‫؍‬ 0.016). The allele frequency of EPEP366-367ins was 0.408 in patients with SLE; this frequency was significantly higher than that in healthy controls (0.312) (P ‫؍‬ 0.006). WEHI-231 cells transfected with EPEP؉ HS1 were 100-fold more sensitive to B cell receptor (BCR)-mediated apoptosis than were those transfected with HS1 without EPEP. B lymphocytes from SLE patients with the EPEP؉ allele were significantly more apoptotic without BCR stimulation and less activated after BCR stimulation than were those from SLE patients without the EPEP allele. Conclusion. These results suggest that HS1 with the EPEP insertion polymorphism transmits accelerated signals from BCR and is involved in the pathogenesis of SLE.Systemic lupus erythematosus (SLE) is a prototypic systemic autoimmune disease characterized by the presence of a variety of autoantibodies. Various genetic and environmental factors, including B cell hyperactivity, T cell dysfunction, and cytokine dysregulation, initiate immune activation in SLE that culminates in organ inflammation and damage (1-9). It has been considered that B cells are innocent bystanders that are activated secondarily by autoreactive T lymphocytes. However, recent evidence from the study of human SLE and its murine models suggests that B lymphocytes are intrinsically defective and are primarily essential for the maintenance of activated/memory T cells by presenting antigens to T cells.B cells from mice deficient in Lyn (10-12), CD22 (13-16), SHP-1 (17,18) exhibit a hyperreactive phenotype and produce autoantibodies. Indeed, Lyn-deficient mice demonstrate activation of autoreactive B cells and subsequent SLE-like symptoms, such as the production of anti-double-stranded DNA (anti-dsDNA)

Interactions among HCLS1, HAX1 and LEF-1 proteins are essential for G-CSF–triggered granulopoiesis

“…The allele frequency of HCLS1 Glu-Pro-Glu-Pro366-367ins was also significantly higher in patients with AML as compared with healthy individuals (35.2% versus 21.5%, odds ratio 1.7; P = 0.0005313). Notably, the high frequency of this insertion was previously described in patients with systemic lupus erythematosus and HCLS1 containing the inserted amino acids was shown to enhance B cell receptor signaling in B lymphocytes, inducing receptor- independent activation 48 . Similar mechanisms of HCLS1 hyperactivation could be applicable to AML blasts.…”

“…Moreover, we identified an insertion in the proline-rich region of HCLS1 in a majority of patients with AML. This insertion was previously identified in a mouse immature B lymphoma cell line in which it induced enhanced BCR-mediated signal transduction 48 . In AML, this insertion may lead to hyperactivation of cytokine signaling.…”

T-cell-receptor-dependent actin regulatory mechanisms

“…As described below, this region is also involved in regulation of HS1 by tyrosine phosphorylation. Intriguingly, very near the regulatory tyrosine residues is a polymorphic region containing glutamic acid-proline repeats (EP6 or EP8) that is genetically linked to Systemic Lupus Erythematosus (Otsuka et al, 2004). Expression of the diseaseassociated HS1 variant in B cells leads to enhanced apoptosis, but it is currently unclear how it affects cytoskeletal dynamics.…”

Familial aggregation and linkage analysis of autoantibody traits in pedigrees multiplex for systemic lupus erythematosus

“…Interestingly, the hematopoietic cellspecific Lyn substrate 1 (HS1) gene lies in this interval and has been associated with SLE. 91 This gene plays an important role in lymphocyte signaling through the Bcell receptor (BCR). Polymorphisms identified in SLE patients are thought to accelerate BCR-mediated signaling and contribute to increased rates of apoptosis.…”