We investigated the expression of the retinoblastoma protein (pRB) in adipocytes and its possible interaction with the adipogenic transcription factor CCAAT/enhancer-binding protein α (C/EBPα) in controlling the acquisition of the terminally differentiated adipocyte phenotype. The pRB was expressed (as measured by immunoblotting and/or immunofluorescence) in mice brown and white adipose tissue and in cultured adipocytes that showed lipid accumulation and expressed specific differentiation markers such as aP2 (measured using a specific cDNA probe) and in the case of brown adipocytes UCP-1 (measured using specific antibodies), but was undetectable in proliferative undifferentiated preadipocytes. Transient transfection experiments revealed a functional interaction between pRB and C/EBPα affecting transcription from the ucp-1 gene promoter. Thus, in immortalized brown adipocytes, co-transfection of both a C/EBPα and a pRB expression vectors maximally enhanced the expression of reporter chloramphenicol acetyltransferase driven by the ucp-1 promoter. Interestingly, C/EBPα inhibited reporter gene expression in CHO cells in an effect that was also potentiated in the presence of pRB. A positive effect of pRB on transcription from the ucp-1 promoter could be detected in C/EBPα-/- fibroblasts only after forced to overexpress C/EBPα, suggesting that the effect of pRB is dependent on its interaction with C/EBPα. We also found evidence that pRB and C/EBPα can directly bind to each other in vitro. Our results show that the expression of pRB is restricted to differentiated adipocytes, and provide evidence of a physical and functional interaction between pRB and C/EBPα that affects the transcriptional activity of the later on a brown adipocyte-specific gene.
|Original language||English (US)|
|Number of pages||7|
|Journal||European Journal of Cell Biology|
|State||Published - 1998|
- Cell growth
ASJC Scopus subject areas
- Cell Biology