SUPPRESSION OF MAFS EXPRESSION BY THE SIRNA TECHNIQUE ALTERS THE GENE PROFILE RELATED TO PANCREATIC ENDOCRINE HORMONE AND ADIPOCYTOKINE IN VIVO AND IN VITRO

Abstract

One of the large maf molecules, mafA, is a strong transactivator of insulin, and other mafs, including mafB and c-maf, have been found to be involved in the regulation of pancreatic development and function. In a previous study we established an mRNA interference technique that makes it possible to modify the level of targeted mRNAs in the mouse in vivo. An expression vector carrying synthetic maf-siRNA was rapidly injected into the tail vein of 8-week-old-mice (Hydrodynamic method), and the resulting alteration of the gene profile was analyzed with a microarray system. Suppression of the mafA mRNA level in the pancreas by siRNA resulted in down-regulation of insulin and glucagon mRNA and of the mRNA of the adipocytokines adipsin and adiponectin. Thus, mafA is likely to be involved in the regulation of adipocytokines as well as pancreatic endocrine hormone. In a preliminary experiment we found that transfection of adipocytes with mafA siRNA in vitro attenuated adipocyte differentiation and downregulated adipokine gene expression. On the other hand, the c-maf expression level in the pancreas of c-maf-siRNA-treated mice was approximately 50% reduced in comparison with stop-siRNA-treated animals. Microarray analysis revealed down-regulation of expression of the insulin and glucagon genes in the pancreas of siRNA-treated mice, while Ddit3 and Nurp1 (Ddit3 having a p53 binding site, encodes an inhibitor of C/EBP and Nurp1 is a transcriptional cofactor activated in acinar cells of pancreatitis) were upregulated, and HSP8 expression was down-regulated. Moreover, several genes coding kallikrein 1-related peptidase (Klk1b4, Klk1b8, Klk1b11 and Klk1b24), that locate on kallikrein 1 locus (chr.19q13.3-13.4) and code serin protease protein without proven kininogenase activity were down-regulated in the pancreas. This study demonstrated that reduction of mafA and c-maf RNA levels altered expression of genes that code pancreatic hormones, including insulin and glucagon. The results of this study also suggest that mafA may regulate several adipocytokines in the pancreas and that c-maf may not only regulate endocrine hormones in the pancreas but serine proteases as well. Taken together, the findings in this study suggested there the involvement of a network of transcriptional factors, mafs, pancreatic endocrine hormones, and adipocytokines in glucose and lipid metabolism.