NOVEL ALTERNATIVE SPLICE VARIANTS OF CGMP-BINDING CGMP-SPECIFIC PHOSPHODIESTERASE

After our recent findings that the amino-terminal portion of rat cGMP- binding, cGMP-specific phosphodiesterase (cGB-PDE) differs from those of bovine and human cGB-PDEs, we found two forms of canine cGB-PDE cDN As (CFPDEA1 and CFPDE5A2) in canine lung, Each contained a distinct am ino-terminal sequence, CFPDE5A1, possessing an amino-terminal portion with sequence similar to those of bovine and human, and CFPDE5A2, havi ng one similar to that of rat, Other portions coding for the cGMP bind ing domains and the catalytic domain mere conserved. Both CFPDE5A1 and CFPDE5A2 transcripts were detected in the cerebellum, hippocampus, re tina, lung, heart, spleen, and thoracic artery. CFPDE5A1 transcripts w ere particularly abundant in the pylorus, whereas CFPDE5A2 transcripts were quite low in this tissue. CFPDE5A1 and CFPDE5A2 expressed in COS -7 cells had cGMP K-m values of 2.68 and 1.97 mu M, respectively, and both were inhibited by a low concentration of a cGB-PDE inhibitor, Zap rinast. Both CFPDE5A1 and CFPDE5A2 bound cGMP to their allosteric cGMP binding domains, and this cGMP binding was stimulated by 3-isobutyl-1 -methylxanthine. Thus, two types of alternative splice variants of can ine cGB-PDE have been identified and shown to have similar biological properties in vitro.