Expression and transcriptional regulation of the PD-Ialpha/autotaxin gene in neuroblastoma

Autotaxin (ATX) is a newly found autocrine tumor cell motility-stimulating factor. ATX is a member of the ecto-phosphodiesterase I (PD-I)/ nucleotide pyrophosphatase family. PD-Ialpha was found as a brain-type ecto-phosphodiesterase I/nucleotide pyrophosphatase. ATX and PD-Ialpha are alternative splicing products from one gene. ATX stimulates motility of A2058 melanoma cells in vitro; however, it has not been known if PD-Ialpha/ATX is expressed in naturally occurred human tumors. In this study, we examined the expression of the human PD-Ialpha/ATX gene in human neuroblastoma tumor tissues and the motility stimulating activity of recombinant ATX on neuroblastoma cells and investigated its transcriptional regulatory mechanism in a human neuroblastoma cell line. The PD-Ialpha/ATX gene was expressed in the primary tumor tissues from neuroblastoma patients to varying degrees. This gene is also expressed in the SMS-KAN neuroblastoma cell line. We identified both isoforms, PD-Ialpha and ATX, in these tumor tissues and SMS-KAN cells. The recombinant ATX stimulated the motility of SMS-KAN cells at low nanomolar concentration. We situated the promoter region, which is essential for its transcription in SMS-KAN cells, at -287 to -254 nucleotides by the promoter activity assay. The gel-shift assay revealed that there exists a nuclear protein in SMS-KAN cells that binds this region. These new insights about autocrine tumor cell motility-stimulating protein will help us to understand the metastatic mechanism of human neuroblastoma.