Molecular and functional characterization of galectin 9 mRNA isoforms in porcine and human cells and tissues

To characterize the possible multiple implications of galectin 9, described as eosinophil chemoattractant protein as well as urate transporter/channel, the porcine homologue of galectin 9, Gal9p, was cloned from LLC-PK(1) cells and stably expressed in human embryonic kidney 293 cells. Significant Gal9p-mediated transport could be demonstrated for [(14)C]-uric acid and for [(14)C]-PAH(1). Transport was dependent on imposed changes of membrane potential of the host cells, but did not follow the classical carrier criteria. Gal9p-mRNA (1573 bp) as well as a 96 bp-elongated isoform show highest abundance in organs of the gastrointestinal tract, to a lesser extent in the aorta and the liver. RT-PCR on human tissue let to the identification of galectin 9 mRNA in human kidney, in HUVEC and in prototype cells of the monocyte/macrophage system (U-937, HL60). In HUVEC, three constitutively expressed galectin 9 mRNA-isoforms were identified. On the basis of the functional characteristics together with a detailed sequence analysis along the galectin family, different domains of galectin 9 are discussed. The data of the present study sustain the idea of the involvement of galectin 9 in immune/inflammation processes and in potential-sensitive uric acid translocation.