High Expression of ENPP2/Autotaxin in Patients with FLT3-ITD Positive Acute Myeloid Leukemia.

The Fms-like tyrosine kinase 3 (FLT-3) receptor tyrosine kinase acts as an important player in controlling the growth and differentiation of haematopoietic progenitor cells. It was shown that activating mutations of FLT-3 are involved in the pathogenesis of acute myeloid leukemia (AML). The most frequent aberration is an internal tandem duplication (ITD) of the juxtamembrane domain coding sequence, which is present in up to 27% of the patients with AML and has been associated with poorer prognosis. To further understand the factors involved, we performed microarray analysis to identify genes specifically upregulated in cases with FLT3-ITD mutations. One gene we identified was ENPP2/Autotaxin (ENPP2/ATX). The ENPP2/ATX protein acts as a lysophospholipase D through generating lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P). These two bioactive small lipids have crucial functions in cell migration and proliferation and act via G-protein coupled receptors. ENPP2/ATX has been associated with tumor cell migration in several solid tumors, expression has not been reported in myeloid cells before. The aim of the current study was to investigate the expression pattern of ENPP2/ATX in normal haematopoiesis and leukemia as well as its role in the pathogenesis of AML. Real-Time PCR analysis of 215 primary AML samples from all major cytogenetic risk groups confirmed a significant upregulation in FLT3-ITD patients. High expression was also found in cases with complex karyotype and −5 and −7, but not in cases with good risk cytogenetics. To explore the function of ENPP2/ATX in the haematopoietic system, we stably overexpressed two different splice variants of ENPP2/ATX in several leukemic cell lines. The expression was detected at both, mRNA and protein level by RT-PCR and Western blot analyses, respectively. The lysophospholipase D activity of the protein could be measured by a functional assay using an artificial substrate for ENPP2/ATX. Transwell migration assays showed an increased migration capacity of cells with high expression of ENPP2, which indicates that the overexpressed protein is functional. Based on our results, we suggest that ENPP2/ATX is involved in leukemic cell migration. Our findings point to a close link between ENPP2/ATX and FLT3 in the pathogenesis of AML. Current work focuses on its role in cell survival and prognosis.