The G Protein-Coupled Receptor cysLT1 Is Expressed in Acute Myeloid Leukemia Mediating Cell Migration and Survival.

Abstract

Previous studies have shown that the G protein-coupled receptor (GPCR) cysLT1, which recognizes inflammatory lipid mediators (cysteinyl-leukotrienes), is expressed in immature hematopoietic and tumor (eg. colon cancer) cells. In the present study, we analyzed leukemic blasts from 19 patients with newly diagnosed acute myeloid leukemia for analysis of expression and function of cysLT1. By RT-PCR, cysLT1 mRNA was found in all primary AML cells. Quantitative TaqMan PCR demonstrated high levels particularly in acute myeloblastic leukemia without maturation (FAB M1). There was also a positive correlation between the cysLT1 mRNA level and the expression of CD34 and CD-117 (c-kit), indicating that high cysLT1 expression corresponds to an AML phenotype resembling normal hematopoietic progenitor cells. CysLT1 was functionally active in AML blasts, as demonstrated by intracellular calcium fluxes and actin polymerization induced by the ligand LTD4. Similar to mRNA expression, strongest responses were seen in AML FAB M1. As LTD4 can be produced in the bone marrow by stromal cells and may contribute to bone marrow infiltration of AML, chemotaxis was analyzed. Surprisingly, already low concentrations (10nM) induced significant chemotaxis of AML blasts, while higher concentrations (up to 1 uM) were less effective in a dose-dependent manner. Incubation of myeloid leukemic cell lines (eg. KG1a) and primary AML blasts with the specific cysLT1 antagonist MK571 resulted in significantly reduced viability after 48 h in a dose-dependent manner (10nM-10uM), suggesting also an autocrine function of cysLT1 ligands. To explore signal transduction pathways involved in leukemic cell proliferation and chemotaxis, we found that in AML cell lines, LTD4 induced phosphorylation of Erk/MAP kinase, wich is related to proliferation, and Pyk2, which represents a focal adhesion kinase-like signaling molecule that links GPCRs with cell migration, while the Akt pathway was not involved. We conclude that cysLT1 is consistently expressed in acute myeloid leukemia, and mediates both chemotactic and proliferative responses. Therefore, cysLT1 antagonists, which are already used in the treatment of allergy, may improve the effectiveness of antileukemic therapy.