CCAAT/enhancer binding protein expression is rapidly extinguished in TA1 adipocyte cells treated with tumor necrosis factor.

Tumor necrosis factor (TNF) has been shown to have diverse effects on a wide variety of cell types. In the mouse adipogenic TA1 cell line, TNF completely abolishes differentiation and reverts fully differentiated fat cells into fibroblasts. This block in differentiation and its reversal is due to the rapid reduction in the expression of adipose-specific genes. This study reports that the transcription factor, CCAAT/enhancer binding protein (C/EBP), previously reported to promote the differentiation of 3T3-L1 adipocytes, is expressed in TA1 cells. During their growth in culture, the levels of C/EBP, as evidenced by its cellular levels of specific mRNA, protein, and DNA binding activity, increase dramatically when cells reach confluence and proceed to differentiate. Addition of TNF to cultured preadipocytes or fully differentiated adipocytes rapidly reduces C/EBP levels and is accompanied by the decrease in expression of adipose-specific genes. C/EBP binding sites occur in several adipose-specific genes, and here it is demonstrated that its presence in a novel adipose-specific gene, Clone 47, also referred to as FSP27, may be responsible for the strong down-regulation of the expression of the Clone 47 (FSP27) promoter-linked chloramphenicol acetyl transferase gene by TNF. This study proposes that the loss of C/EBP in response to TNF treatment may in part explain the loss of the adipocyte differentiated state.