Soluble Human Leukocyte Antigen-G5 Activates Extracellular Signal-Regulated Protein Kinase Signaling and Stimulates Trophoblast Invasion

Abstract

Soluble human leukocyte antigen-G (HLA-G) is a non-classical class Ib HLA molecule that is secreted from blastocysts. Soluble HLA-G modulates the immune tolerance of the mother and can be used as a prognostic factor for the clinical pregnancy rate. However, the underlying mechanism of how soluble HLA-G5 affects pregnancy remains largely unknown. We hypothesized that soluble HLA-G5 promotes successful implantation and pregnancy by modulating trophoblast invasion through receptor binding and activation of extracellular signal-regulated protein kinase (ERK) signaling pathway. Recombinant HLA-G5 protein over-expressed in E. coli BL21 was purified to near homogeneity. We studied the expression of HLA-G5 and its receptors, the leukocyte immunoglobulin-like receptor subfamily B1 (LILRB1) and killer cell immunoglobulin-like receptor 2DL4 (KIR2DL4), in primary trophoblasts and trophoblastic (JAr and JEG-3) cell lines by florescence-labeled HLA-G5. HLA-G5 was detected in the primary trophoblasts and JEG-3 cells. The LILRB1 and KIR2DL4 receptors were expressed in both primary trophoblasts and trophoblastic cell lines. HLA-G5 stimulated cell invasion (p<0.05) and increased urokinase (uPA) and matrix metalloproteinases (MMPs) transcripts and their activity (p<0.05) in trophoblastic cells. HLA-G5 activated the ERK signaling pathway and induced ERK1/2 phosphorylation in the trophoblastic cell lines. Addition of ERK inhibitors (U0126 and PD98059) nullified the stimulatory effect of HLA-G5 on trophoblastic cell invasion. Taken together, HLA-G5 induced trophoblast invasion by binding to KIR2DL4 and LILRB1, by increasing uPA and MMPs expressions and by activating the ERK signaling pathway.

Human Leukocyte Antigen-G (HLA-G) Expression in Cancers: Roles in Immune Evasion, Metastasis and Target for Therapy

“…Furthermore, knockdown of the HLA-G-induced MMP-15 expression significantly decreased cell migration and tumor metastasis (18). In accordance with our findings, HLA-G5 was documented to stimulate primary trophoblasts and trophoblastic cell line (JAR and JEG-3) invasion and to increase MMP-2 transcripts and their activity by binding to KIR2DL4 and ILT2 (22). In another study, suppression of HLA-G expression in JEG-3 cells was observed to …”

Immunoregulatory Function of HLA-G in Gastric Cancer

“…It modulates the immune tolerance of the mother (Guo et al, 2013). HLA-G expression is a valuable noninvasive embryo marker to assist in improving pregnancy outcomes (Kotze et al, 2013).…”

Possible Role of HLA-G, LILRB1 and KIR2DL4 Gene Polymorphisms in Spontaneous Miscarriage

“…Whether scenario, in which the paternal KIR2DL4 allele inherited by the fetus could have an impact on NK cells responses in the developing fetus is likely, remains to be elucidated. However, the expression of KIR2DL4 and LILRB1 receptors in both primary trophoblasts and trophoblastic cell lines (JAr and JEG-3) has been described by Guo et al (2013). Moreover, these receptors were functional as trophoblast invasion was induced by binding soluble HLA-G5 to KIR2DL4 and LILRB1.…”