Molecular cloning, expression, and localization of a brain-specific phosphodiesterase I/nucleotide pyrophosphatase (PD-I alpha) from rat brain.

We have isolated cDNA clones encoding the rat brain phosphodiesterase I/nucleotide pyrophosphatase (PD-I alpha), a novel member of the membrane phosphodiesterase I gene family. PD-I alpha cDNA has a 2,655-nucleotide open reading frame encoding a polypeptide of 885 amino acids with a calculated M(r) of 101,302. Northern blot analysis revealed that PD-I alpha transcript was abundantly present in cerebrum and cerebellum while its level was quite low in other tissues. In situ hybridization analysis revealed that PD-I alpha mRNA is localized in secretory epithelial cells in the brain and the eye including choroid plexus epithelial cells, ciliary epithelial cells, iris pigment epithelial cells, and retinal pigment cells. Localization of PD-I alpha mRNA was also observed in glial cells in the molecular layer of the cerebellum. These results indicate that this protein might be involved in the synthesis of adenosine as well as in the regulation of the secretion/transport of epithelial cells and glial cells in the central nervous system.