Cyclic nucleotide phosphodiesterases (PDEs) are critical regulators of intracellular concentrations and biological effects of cAMP and cGMP. Understanding cellular expression and regulation of PDE isoforms [which belong to eleven gene families (PDEs 1-11)] will be of increasing importance for targeting specific PDEs in treating various diseases, including pulmonary disorders. PDE3B appears (or greatly increases in activity) during differentiation of cultured human adipocytes, murine 3T3-L1 adipocytes, or human monocyte-derived macrophages. Our results suggest that cAMP (accumulating in response to IBMX) plays a crucial role in regulation of PDE3B expression during differentiation of 3T3-L1 adipocytes, and induction of PDE3B does not seem to be directly linked to accumulation of lipid. Our results also indicate that insulin-induced activation of PDE3B is mediated by PI3-K- and PKB-dependent signals, and may be related to IRS-1 induced translocation of signaling molecules to intracellular membranes, where PDE3B may be activated by PKB. In addition a portion of the intracellular pool of PKB is found in association with intracellular membranes, co-elutes with membrane-associated PDE3B during gel filtration chromatography of solubilized 3T3-L1 microsomal membranes, and co-immunoprecipitates with PDE3B. The structural determinants for this latter interaction reside in the N-terminal regulatory region of PDE3B and PH-domain of PKB; proline-rich peptide sequences from the N-terminal region seem to inhibit interactions between PDE3B and PKB. To further examine functional roles of PDE3 isoforms, mice with targeted disruptions of PDE3A and PDE3B genes have been generated. Female PDE3A KO mice are sterile, most likely because the absence of functional PDE3A in oocytes leads to increased cAMP, activation of Protein kinase A (PKA), and inhibition of Maturation-promoting factor/ MAP-kinase signals that are important in meiotic progression , oocyte maturation (marked by germinal vesicle breakdown (GVBD)), and subsequent fertilization. Consistent with this hypothesis, treatment of PDE3A KO oocytes with PKA inhibitors reinitiates meiotic progression, and restores competency for fertilization in vitro. PDE3B KO mice seem to accumulate less fat and exhibit signs of disruption of insulin homeostatic mechanisms and insulin resistance. Administration of a Beta-3 agonist to intact mice results in a much larger increase in serum insulin but relatively less glucose disposal in PDE3B KO mice, which also demonstrate aberrant i.p. insulin tolerance tests with respect to reduction in blood glucose. Hyperinsulinemic-euglycemic clamps indicate that insulin is much less effective in inhibiting endogenous glucose production in KO mice. Studies are ongoing to understand the roles of PDE3A and PDE3B in these and other phenotypic changes.
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