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Autotaxin (ATX), a potent tumor motogen, augments invasive and metastatic potential of ras-transformed cells.
Autotaxin (ATX), an exo-nucleotide pyrophosphatase and phosphodiesterase, was originally isolated as a potent stimulator of tumor cell motility. In order to study whether ATX expression affects motility-dependent processes such as invasion and metastasis, we stably transfected full-length ATX cDNA into two non-expressing cell lines, parental and ras-transformed NIH3T3 (clone7) cells. The effect of ATX secretion on in vitro cell motility was variable. The ras-transformed, ATX-secreting subclones had enhanced motility to ATX as chemoattractant, but there was little difference in the motility responses of NIH3T3 cells transfected with atx, an inactive mutant gene, or empty vector. In MatrigelTM invasion assays, all subclones, which secreted enzymatically active ATX, demonstrated greater spontaneous and ATX-stimulated invasion than appropriate controls. This difference in invasiveness was not caused by differences in gelatinase production, which was constant within each group of transfectants. In vivo studies with athymic nude mice demonstrated that injection of atx-transfected NIH3T3 cells resulted in a weak tumorigenic capacity with few experimental metastases. Combination of ATX expression with ras transformation produced cells with greatly amplified tumorigenesis and metastatic potential compared to ras-transformed controls. Thus, ATX appears to augment cellular characteristics necessary for tumor aggressiveness.
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