| dc.description.abstract | Cyclic nucleotide phosphodiesterase 3B (PDE3B), a PDE3 family isozyme that hydrolyzes cAMP with high affinity, plays an important role in the regulation of energy homeostasis in adipocytes mainly through regulation of lipolysis, lipogenesis, gluconeogenesis, and glucose uptake. It is known that increasing intracellular cAMP concentration by inhibition of PDE3B triggers rapid lipid degradation, whereas decreasing cAMP level leads to antilipolytic action and lipogenesis. However, the proteins that are regulated by PDE3B in these lipid metabolic processes remain largely undefined. In this study, we used two-dimensional (2-D) gel electrophoresis and mass spectrometry to identify the proteins expressed in mouse 3T3-L1 adipocytes in the presence of the PDE3 inhibitor cilostazol. The initial results showed that three proteins were upregulated in 3T3-L1 cells after treatment with cilostazol and insulin for 18 h. Comparing to the 2-D gel results derived from the cells treated with insulin alone indicates that two of the three proteins were induced in expression by cilostazol. Following the mass spectrometry analysis, these proteins were identified as annexin a2 (ANX A2) and nucleoside diphosphate kinase b (NDPK-B). The third protein upregulated in the presence of cilostazol and insulin was not identified by the method. Further analysis by real-time PCR revealed that ANX A2 and NDPK-B mRNA expression was also upregulated by cilostazol. In a separate experimental setting, 3T3-L1 adipocytes were treated with cilostazol and the β-adrenergic receptor agonist isoproterenol (ISO) for 8 h, followed by 2-D gel analysis. The results showed that in the presence of ISO one protein was upregulated by cilostazol, and mass spectrometry identified it as thioredoxin-1 (TXN-1). This induction in TXN-1 protein also was associated with an increase in mRNA expression. Both TXN-1 and NDPK-B have been shown to inhibit lipogenesis in adipocytes. Thus, we rationalize that inhibition of PDE3B to induce TXN-1 and NDPK-B expression is a mechanism underlying the blockage of lipogenesis by cilostezol. In addition, ANX A2 is implicated in GLUT4 translocation in adipocytes, pointing to a potential role of PDE3 inhibitors in regulation of glucose transport via enhancing ANX A2 expression. This proposed effect, however, awaits further experimental attestation. | en_US |