Biochemical and Biophysical Research Communications, Vol.522, No.3, 770-775, 2020
Intracellular cAMP contents regulate NAMPT expression via induction of C/EBP beta in adipocytes
A decline in intracellular nicotinamide adenine mononucleotide (NAD(+)) causes adipose tissue dysfunction. Nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the rate-limiting step in the NAD(+) biosynthesis pathway. However, the molecular mechanism that mediates regulation of NAMPT expression in adipocytes is yet to be elucidated. This study found that intracellular cAMP regulates NAMPT expression and promoter activity in 3T3-L1 adipocytes. cAMP-mediated Nampt promoter activity was suppressed by protein kinase A inhibitor H89, whereas AMP-activated protein kinase inhibitor compound C did not affect cAMP-mediated Nampt promoter activity. Intracellular cAMP induced CCAAT/enhancer-binding protein beta (C/EBP beta) expression. Knockdown of C/EBP beta suppressed NAMPT expression and promoter activity. Furthermore, the Nampt promoter was activated by C/EBP beta, while LIP activated the dominant-negative form of C/EBP beta. Promoter sequence analysis revealed that the region from -96 to -76 on Nampt was required for C/EBP beta-mediated promoter activity. Additionally, chromatin immunoprecipitation assay demonstrated that C/EBP beta was bound to the promoter sequences of Nampt. Finally, NAMPT inhibitor FK866 suppressed adipogenesis in 3T3-L1 cells, and this suppressive effect was restored by nicotinamide mononucleotide treatment. These findings showed that intracellular cAMP increased NAMPT levels by induction of C/EBP beta expression and indicated that the induction of NAMPT expression was important for adipogenesis. (C) 2019 Elsevier Inc. All rights reserved.