Characterization of an alternative splice variant of human nucleoside triphosphate diphosphohydrolase 3 (NTPDase3): A possible modulator of nucleotidase activity and purinergic signaling

Nucleoside triphosphate diphosphohydrolase 3 (NTPDase3) is a cell surface, membrane-bound enzyme that hydrolyzes extracellular nucleotides, thereby modulating purinergic signaling. An alternatively spliced variant of NTPDase3 was obtained and analyzed. This alternatively spliced variant, termed NTPDase3 beta, is produced through the use of an alternative terminal exon (exon 11) in place of the terminal exon (exon 12) in the full-length NTPDase3, now termed NTPDase3 alpha. This results in an expressed protein lacking the C-terminal cytoplasmic sequence, the C-terminal transmembrane helix, and apyrase conserved region 5. The cDNA encoding this truncated splice variant was detected in a human lung library by PCR. Like the full-length NTPDase3 alpha, the alternatively spliced NTPDase3 beta was expressed in COS cells after transfection, but only the full-length NTPDase3 alpha is enzymatically active and properly trafficked to the plasma membrane. However, when the truncated NTPDase3 beta was co-transfected with full-length NTPDase3 alpha, there was a significant reduction in the amount of NTPDase3 alpha that was properly processed and trafficked to the plasma membrane as active enzyme, indicating that the truncated form interferes with normal biosynthetic processing of the full-length enzyme. This suggests a role for the NTPDase3 beta variant in the regulation of NTPDase3 nucleotidase activity, and therefore the control of purinergic signaling, in those cells and tissues expressing both NTPDase3 alpha and NTPDase3 beta. (c) 2006 Elsevier Inc. All rights reserved.