Murine and human autotaxin α, β, and γ isoforms -: Gene organization, tissue distribution, and biochemical characterization

Autotaxin is a type II ectonucleotide pyrophosphate phosphodiesterase enzyme. It has been recently discovered that it also has a lysophospholipase D activity. This enzyme probably provides most of the extracellular lysophosphatidic acid from lysophosphatidylcholine. The cloning and tissue distribution of the three isoforms (imaginatively called alpha, beta, and gamma) from human and mouse are reported in this study, as well as their tissue distribution by PCR in the human and mouse. The fate of the alpha isoform from human was also studied after purification and using mass spectrometry. Indeed, this particular isoform expresses the intron 12 in which a cleavage site is present, leading to a rapid catabolism of the isoform. For the human isoform gamma and the total autotaxin mRNA expression, quantitative PCR is presented in 21 tissues. The isoforms were expressed in two different hosts, insect cells and Chinese hamster ovary cells, and were highly purified. The characteristics of the six purified isoforms (pH and temperature dependence, K-m and V-max values, and their dependence on metal ions) are presented in this study. Their sensitivity to a small molecule inhibitor, hypericin, is also shown. Finally, the specificity of the isoforms toward a large family of lysophosphatidylcholines is reported. This study is the first complete description of the reported autotaxin isoforms.