We have been studying tumor cell motility as a component of the process of metastasis with a special emphasis on factors that could regulate this motility. To this end, we initially purified autotaxin, a tumor-secreted motility-stimulating glycoprotein, from the conditioned medium of a human melanoma cell line. We have now cloned and sequenced autotaxin and found that it is homologous to the B cell differentiation antigen, PC-1, as well as to other type I phosphodiesterases. In addition to the original melanoma cell line which was both a source and a responder for autotaxin, we have cloned autotaxin from breast and teratocarcinoma lines. Northern blot analysis of multiple normal tissues indicated that this protein has the highest steady state levels in ovary, small intestine, brain and placenta. We have also found that certain breast carcinoma and neuroblastoma cells, as well as HUVEC's (human umbilical vein cells), respond to autotaxin as a chemoattractant. We have also begun to explore autotaxin's interactions with nucleotides. We have found that autotaxin possesses type I phosphodiesterase, ATPase, nucleotide pyrophosphatase, autophosphorylation, and ATP binding activities. Utilizing site-directed mutagenesis, we explored the relationship between the enzymatic properties of autotaxin and its capacity to stimulate motility. We found that a single point mutation in the phosphodiesterase catalytic site (Thr210-Ala or Asp) inhibited its phosphodiesterase, autophosphorylation, and motility-stimlating activities but had no effect on ATP binding. A second point mutation (Lys209-Leu) inhibited autophosphorylation but not motility stimulation or phosphodiesterase. Therefore, an intact phosphodiesterase catalytic site is necessary for motility, but phosphorylation of the molecule does not appear to be a prerequisite. Finally, we have found that AMP and adenosine are chemoattractants for the human melanoma cell line, A2058. These molecules, which are products of autotaxin's interaction with ATP, appear to act through an A1 adenosine receptor. Inhibitors of AMP/adenosine A1 receptors block the motility response to AMP/adenosine but have no effect on the motility response to autotaxin.
| Clair, Timothy; Aoki, Junken; Koh, Eunjin et al. (2003) Autotaxin hydrolyzes sphingosylphosphorylcholine to produce the regulator of migration, sphingosine-1-phosphate. Cancer Res 63:5446-53 |
| Woodhouse, Elisa C; Fisher, Amy; Bandle, Russell W et al. (2003) Drosophila screening model for metastasis: Semaphorin 5c is required for l(2)gl cancer phenotype. Proc Natl Acad Sci U S A 100:11463-8 |
