Norepinephrine specifically stimulates ribonucleotide reductase subunit R2 gene expression in proliferating brown adipocytes: mediation via a cAMP/PKA pathway involving Src and Erk1/2 kinases.
We have examined whether a qualitative switch occurs in the response of the ribonucleotide reductase (RNR) genes to the effect of the physiological cAMP-elevating agent norepinephrine (NE) during the development of brown adipocytes. Basal expression of the genes for both RNR subunits, R1 and R2, was high in proliferating cells, but was markedly down-regulated in parallel with adipocyte differentiation. NE stimulation, which promotes DNA synthesis and proliferation of brown preadipocytes, resulted in an increased expression of the R2 gene in proliferating cells (1.6-fold), but was without effect on R1 expression. In contrast, NE stimulation of confluent differentiating brown adipocytes reduced both R1 and R2 expression. The NE stimulation of R2 expression in preadipocytes was mimicked by forskolin and abolished by H89, demonstrating mediation via cAMP and protein kinase A (PKA). Also, inhibitors of Src and of Erk1/2 kinases markedly reduced NE-stimulated R2 expression. We conclude that adrenergic stimulation of brown adipocytes by NE specifically elevates expression of the RNR subunit R2 gene in the proliferative stage of brown adipocyte development, the mediating pathway being a cAMP/PKA cascade further involving Src and the MAP kinase Erk1/2. These results suggest that adrenergic stimulation of brown adipocyte proliferation may act at the level of gene expression of the limiting subunit for RNR activity, R2, and demonstrate a qualitative switch in the response of the R2 gene to cAMP-elevating agents as a consequence of the switch from proliferating to differentiating cell status.
Fredriksson
J Magnus
JM
The Wenner-Gren Institute, Stockholm University, Stockholm, SE-106 91, Sweden.
Nedergaard
Jan
J
D017667:Adipocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D002001:Adipose Tissue, Brown / Q000166:cytology / Q000201:enzymology* / Q000254:growth & development*; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D002455:Cell Division / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D008815:Mice, Inbred Strains; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism* / Q000494:pharmacology; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D012264:Ribonucleotide Reductases / Q000235:genetics*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology; D019061:src-Family Kinases / Q000187:drug effects / Q000378:metabolism
D012333:RNA, Messenger; D000242:Cyclic AMP; D012264:Ribonucleotide Reductases; C108427:ribonucleotide reductase R2 subunit; D019061:src-Family Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D009638:Norepinephrine