MOLECULAR-CLONING AND CHARACTERIZATION OF HUMAN PDE8B, A NOVEL THYROID-SPECIFIC ISOZYME OF 3',5'-CYCLIC NUCLEOTIDE PHOSPHODIESTERASE

We have identified a novel human isozyme of 3',5'-cyclic nucleotide ph osphodiesterase (PDE), which we designated PDE8B, cDNA of 2844 bp enco ding the C-terminal 659 amino acids of PDE8B was cloned following the identification of an expressed sequence tag (EST) obtained through a s earch of the EST database. The predicted protein sequences of PDE8B sh owed highest homology (65% identity, 83% similarity) to that of PDE8A Northern blot analysis indicated that the mRNA encoding PDE8B is expre ssed specifically and abundantly in thyroid gland as a similar to 4.2 kb mRNA, in contrast to the wide expression of PDE8A mRNA in various t issues. The carboxyl-terminal 584 amino acids of PDE8B were expressed in E. coli as a fusion protein. The recombinant PDE8B exhibited cAMP P DE activity which was not inhibited by various PDE inhibitors includin g vinpocetine, milrinone, rolipram, and IBMX with the exception of dip yridamole which caused 50% inhibition at a concentration of 40 mu M. c AMP hydrolytic activity was unaffected by cGMP and no cGMP PDE hydroly sis were detectable at concentrations up to 100 mu M. These findings s uggest that PDE8B is a new member of the PDE8 family. (C) 1998 Academi c Press.