Incubation of rat adipocytes with insulin results in phosphorylation and activation of a membrane-associated cGMP-inhibited phosphodiesterase (cGI or Type III PDE). Activation of this specific cGI PDE is an important component in the antilipolytic action of insulin. In order to gain insight into molecular mechanisms involved in signaling pathways important in regulation of certain biological responses to insulin and to increase an understanding of the structure/function relationships of cGI PDE and mechanisms for its cellular regulation we have cloned the cDNA for the hormone-sensitive adipocyte cGI PDE from rat adipose tissue cDNA libraries. The deduced amino acid sequence of the adipocyte cGI PDE predicts membrane-association domains in the amino-terminal region, a conserved catalytic domain in the carboxyterminal region and three consensus cAMP- dependent kinase (A-kinase) phosphorylation sites in a putative regulatory domain. The mRNA for this cGI PDE is predominantly expressed in rat adipocytes and is dramatically induced during differentiation of 3T3-L1 adipocytes. A partial cDNA clone, encoding a distinct but related cGI PDE was also isolated from a rat adipose tissue cDNA library. This cGI PDE, whose mRNA was not detected in rat or 3T3-L1 adipocytes but was expressed in rat adipose and cardiac tissue, is most likely the rat homolog of a recently cloned human cardiac cGI PDE cDNA (Meacci et al., Proc. Natl. Acad. Sci. USA 89, 3721, 1992). These findings suggest that cGI PDEs are part of a gene family consisting of at least two isoforms.
