Rl. Erickson et al., p300 Coactivates the adipogenic transcription factor CCAAT/enhancer-binding protein alpha, J BIOL CHEM, 276(19), 2001, pp. 16348-16355
Despite the knowledge that CCAAT/enhancer-binding protein alpha (C/EBP alph
a) plays an important role in preadipocyte differentiation, our understandi
ng of how C/EBP alpha interacts with nuclear proteins to regulate transcrip
tion is limited. Based on the hypothesis that evolutionarily conserved regi
ons are functionally important and likely to interact with coactivators, we
compared the amino acid sequence of C/EBP alpha from different species (fr
og to human) and identified four highly conserved regions (CR1-CR4) within
the transactivation domain. A series of amino-terminal truncations and inte
rnal deletion constructs were made creating forms of C/EBP alpha which lack
single or multiple conserved regions. To determine which regions of the C/
EBP alpha transactivation domain are important in its ability to induce spo
ntaneous differentiation of 3T3-L1 preadipocytes, we infected preadipocytes
with expression vectors encoding the C/EBP alpha conserved region mutants
and observed their ability to induce differentiation. We found that CR2 fus
ed to the DNA binding domain is able to induce spontaneous differentiation
independent of the other conserved regions. However, CR2 was not necessary
for the adipogenic action of C/EBP alpha because a combination of CR1 and C
R3 can also induce adipogenesis. Because the transcriptional coactivator p3
00 participates in the signaling of many transcription factors to the basal
transcriptional apparatus, we examined whether functional interaction exis
ts between C/EBP alpha and p300. Cotransfection of p300 with p42C/EBP alpha
results in a synergistic increase in leptin promoter activity, indicating
that p300 acts as a transcriptional coactivator of C/EBP alpha. Analyses us
ing C/EBP alpha conserved region mutants suggest that multiple regions (CR2
and CR3) of the C/EBP alpha transactivation domain functionally interact w
ith p300.