Role of p300, a transcriptional coactivator, in signalling of TGF-beta.
BACKGROUND
Smad proteins are novel transcriptional regulators mediating the signalling of the transforming growth factor-beta (TGF-beta) superfamily. Coactivators such as p300/CBP promote transactivation by various transcription factors through a direct interaction with them. Adenoviral oncoprotein E1A, which binds p300, was shown to inhibit the signalling of TGF-beta. These findings raise the possibility that p300 may be involved in TGF-beta signalling.


RESULTS
We investigated whether p300 is involved in transactivation by Smads. p300 enhanced the Smad-induced transactivation of p3TP-Lux, a TGF-beta responsive reporter. E1A inhibited this enhancement, and the inhibition required its ability to bind p300/CBP. p300 and Smad3, as well as Smad2, interacted in vivo in a ligand-dependent manner. The binding region in Smad3 was its C-terminal half that was previously shown to possess an intrinsic transactivation activity. The binding region in p300 was mapped to its C-terminal 678 amino acids. The minimal Smad2/3-interacting region, as well as the rest of the p300, inhibited the transactivation of p3TP-Lux in a dominant-negative fashion.


CONCLUSIONS
p300 interacted with Smad2 and Smad3 in a ligand-dependent manner, and enhanced the transactivation by Smads. Our results present the molecular basis of the transactivation by Smad proteins.
Nishihara
A
A
Department of Biochemistry, The Cancer Institute, Japanese Foundation for Cancer Research (JFCR), and Research for the Future Program, Japan.
Hanai
J I
JI
Okamoto
N
N
Yanagisawa
J
J
Kato
S
S
Miyazono
K
K
Kawabata
M
M
D017500:Adenovirus E1A Proteins / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D006224:Cricetinae; D004268:DNA-Binding Proteins / Q000378:metabolism*; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism*; D018125:Receptors, Transforming Growth Factor beta / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D051899:Smad2 Protein; D051900:Smad3 Protein; D015534:Trans-Activators / Q000378:metabolism*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism* / Q000494:pharmacology
D017500:Adenovirus E1A Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D018125:Receptors, Transforming Growth Factor beta; D051899:Smad2 Protein; D051900:Smad3 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D008156:Luciferases