Regulated expression of three C/EBP isoforms during adipose conversion of 3T3-L1 cells.

Abstract

In an effort to identify protein factors that play a regulatory role in the differentiation of adipocytes, we have isolated two genes that encode polypeptides related to CCAAT/enhancer-binding protein (C/EBP; hereafter termed C/EBP alpha). The proteins encoded by these C/EBP-related genes, termed C/EBP beta and C/EBP delta, exhibit similar DNA-binding specificities and affinities compared with C/EBP alpha. Furthermore, C/EBP beta and C/EBP delta readily form heterodimers with one another as well as with C/EBP alpha. The transcriptional activating capacity of these two newly identified C/EBP isoforms was demonstrated by transient transfection experiments in which expression vectors encoding C/EBP beta and C/EBP delta were observed to induce transcription from the promoter of the serum albumin gene in cultured hepatoma cells. The mRNAs encoding C/EBP beta and C/EBP delta were detected in a number of tissues, most of which corresponded to sites of expression of C/EBP alpha. The expression pattern of C/EBP beta and C/EBP delta during adipose conversion of 3T3-L1 cells was examined by Western and Northern blotting assays. In contrast to the expression profile of the gene encoding C/EBP alpha, whose product is not detectable until the late phase of adipocyte differentiation, the c/ebp beta and c/ebp delta genes were actively expressed very early during adipocyte differentiation. Moreover, transcription of the c/ebp beta and c/ebp delta genes was observed to be induced directly by adipogenic hormones. The accumulation of C/EBP beta and C/EBP delta reached a maximal level during the first 2 days of differentiation and declined sharply before the onset of C/EBP alpha accumulation. The temporal pattern of expression of these three C/EBP isoforms during adipocyte differentiation may reflect the underpinnings of a regulatory cascade that controls the process of terminal cell differentiation.

FMIP controls the adipocyte lineage commitment of C2C12 cells by downmodulation of C/EBPalpha

“…(4) Ectopic expression of C/ EBPalpha counteracts the FMIP-induced differentiation phenotype and siRNA inhibition of C/EBPalpha partially mimics the effect of FMIP. It has been clearly demonstrated that C/EBPalpha is a key player in adipocyte differentiation (Cao et al, 1991;Lin and Lane, 1994;Hu et al, 1995). For example, fibroblasts differentiated into adipocytes following ectopic expression of C/EBPalpha (Freytag et al, 1994;Park et al, 2004).…”

“…As FMIP influences myeloid differentiation as well, we examined the common key factors in both differentiation systems. One candidate is a protein belonging to the C/EBP family (Cao et al, 1991;Wang et al, 1995;Tenen et al, 1997;Lane et al, 1999), as it has been demonstrated that timely expression of C/ EBPalpha and C/EBPbeta is essential for adipocyte differentiation (Fux et al, 2004;Mori et al, 2005). Therefore, we examined the expression of C/EBPalpha and C/EBPbeta during differentiation in FMIP-overexpressing and knockdown cells.…”

C/EBPαp30 plays transcriptional regulatory roles distinct from C/EBPαp42

“…Expression of antisense C/EBPα RNA prevents both growth arrest and terminal differentiation of 3T3-L1 adipocytes [18]. In addition, C/EBPα is critical in regulating the differentiation of preadipocytes, myeloid cells, hepatocytes and pneumocytes [3,5,[19][20][21][22].…”

The role and regulation of 11β-hydroxysteroid dehydrogenase type 1 in the inflammatory response

“…In cells with more modest levels of C/EBPα or none at all, C/EBPβ, if it receives the appropriate post-translational signals or is increased to sufficiently high levels, activates the 11β-HSD1 P2 promoter. A549 cells contain very low levels of C/EBPα, as do 3T3-L1 preadipocytes (Cao et al, 1991;Li et al, 1995;Sai et al, 2008). C/EBPα, essential for myeloid cell differentiation (Zhang et al, 1997) and a neonatal inflammatory response (Burgess-Beusse and Darlington, 1998) has been shown to decrease the transactivation potential of C/EBPβ through control of isoforms expressed (Burgess-Beusse et al, 1999) and thus may suppress transactivation by C/EBPβ in liver under normal circumstances.…”