REGULATION OF MITOCHONDRIAL BIOGENESIS IN BROWN ADIPOSE-TISSUE - NUCLEAR RESPIRATORY FACTOR-2 GA-BINDING PROTEIN IS RESPONSIBLE FOR THE TRANSCRIPTIONAL REGULATION OF THE GENE FOR THE MITOCHONDRIAL ATP SYNTHASEBETA-SUBUNIT/

The regulation of transcription of the gene for the beta subunit of th e FoF1 ATP synthase (ATPsyn beta) in brown adipose tissue has been stu died as a model to determine the molecular mechanisms for mitochondria l biogenesis associated with brown adipocyte differentiation. The expr ession of the ATPsyn beta mRNA is induced during the brown adipocyte d ifferentiation that occurs during murine prenatal development or when brown adipocytes differentiate in culture, This induction occurs in pa rallel with enhanced gene expression for other nuclear and mitochondri ally-encoded components of the respiratory chain/oxidative phosphoryla tion system (OXPHOS). Transient transfection assays indicated that the expression of the ATPsyn beta gene promoter is higher in differentiat ed HIB-1B brown adipocytes than in non-differentiated HIB-1B cells. A major transcriptional regulatory site was identified between nt -306 a nd -266 in the ATPsyn beta promoter. This element has a higher enhance r capacity in differentiated brown adipocyte HIB-1B cells than in non- differentiated cells. Electrophoretic shift analysis indicated that Sp land nuclear respiratory factor-2/GA-binding protein (NRF2/GABP) were the main nuclear proteins present in brown adipose tissue that bind th is site. Double-point mutant analysis indicated a major role for the N RF2/GABP site in the enhancer capacity of this element in brown fat ce lls. It is proposed that NRF2/GABP plays a pivotal role in the co-ordi nated enhancement of OXPHOS gene expression associated with mitochondr ial biogenesis In brown adipocyte differentiation.