Interaction and functional collaboration of p300 and C/EBPβ

Abstract

Transcriptional coactivators such as p300 and CREB-binding protein (CBP) function as important elements in the transcription factor network, linking individual transactivators via protein-protein interactions to the basal transcriptional machinery. We have investigated whether p300 plays a role in transactivation mediated by C/EBP␤, a conserved member of the C/EBP family. We show that C/EBP␤-dependent transactivation is strongly inhibited by adenovirus E1A but not by E1A mutants defective in p300 binding. Ectopic expression of p300 reverses the E1A-dependent inhibition and increases the transactivation potential of C/EBP␤. Furthermore, we show that C/EBP␤ and p300 interact with each other and demonstrate that the sequences responsible for interaction map to the E1A binding region of p300 and the amino terminus of C/EBP␤. Finally, we show that the minimal C/EBP␤ binding site of p300 acts as a dominant-negative inhibitor of C/EBP␤. These observations identify p300 as a bona fide coactivator for C/EBP␤. C/EBP␤ is highly expressed in the myelomonocytic lineage of the hematopoietic system and cooperates with Myb to activate mim-1, a gene specifically expressed during myelomonocytic differentiation. Recent evidence has shown that Myb recruits CBP (and presumably p300) as a coactivator and, in contrast to C/EBP␤, interacts with the CREB binding site of p300-CBP. We show that p300 not only stimulates the activity of Myb and C/EBP␤ individually but also increases the synergy between them. Thus, our results reveal a novel function of p300: in addition to linking specific transcription factors to the basal transcriptional machinery, p300 also mediates the cooperation between transactivators interacting with different domains of p300.Initiation of transcription by RNA polymerase II involves the cooperation of transcription factors, binding to specific regulatory sequences, with the basal transcriptional machinery. The transcriptional coactivators p300 and the CREB-binding protein (CBP) have been recognized as key molecules involved in the communication between transcription factors and the transcriptional machinery and thus appear to be important elements of gene regulation networks (for a review, see reference 22). p300 was originally identified as a cellular interaction partner of the adenovirus E1A oncoprotein (17), and inactivation of p300 by binding to E1A appears to be one of the mechanisms by which the E1A protein suppresses transcriptional activation of certain promoters (for a review, see reference 35). Since p300 has strong sequence similarity to CBP and exhibits properties similar to those of CBP, p300 and CBP are considered functional homologs (2, 33). Several transcription factors, such as CREB, Jun, Myb, Sap-1a/Elk-1, Fos, p53, MyoD, and the nuclear hormone receptors, have now been shown to require p300 and CBP as coactivators (3-5, 10, 13, 14, 21, 23, 24, 28, 31, 42, 53). p300 and CBP do not by themselves interact with specific DNA sequences; rather, they display a variety of protein interaction surfaces tha...

A Two-Step, PU.1-Dependent Mechanism for Developmentally Regulated Chromatin Remodeling and Transcription of the c-fms Gene

“…We next wanted to investigate why histone acetylation levels were low in PU.1 Ϫ/Ϫ cells and in PUER cells at early time points of OHT induction. This was not due to the absence of nucleosomes, as shown by a ChIP (23,37), and work from our lab demonstrated that active c-fms regulatory elements recruit CBP (9). It has been shown previously that the activity of CBP can be regulated as well (35); it was therefore possible that CBP was recruited but was inactive.…”

Myb binding proteins: regulators and cohorts in transformation

“…Although Myb and CREB bind the same domain of CBP (Dai et al, 1996;Kiewitz and Wolfes, 1997;OelgeschlaÈ ger et al, 1996), the interaction with Myb proteins is constitutive rather than phosphorylation-dependent (Dai et al, 1996;OelgeschlaÈ ger et al, 1996). Interestingly, CBP and p300 can also interact with and stimulate the activity of C/EBPb (Mink et al, 1997;OelgeschlaÈ ger et al, 1996), suggesting that the coactivators may act as a bridge between Myb and C/EBPb (Figure 1). This type of bridging activity could explain the ability of Myb proteins to cooperate with C/EBPb and a wide variety of other transcription factors, in the context of di erent promoters.…”

“…This type of bridging activity could explain the ability of Myb proteins to cooperate with C/EBPb and a wide variety of other transcription factors, in the context of di erent promoters. CBP and p300 bind the transactivation domains of c-Myb and C/EBPb, located in their central and N-terminal domains, respectively (Dai et al, 1996;Kietwitz and Wolfes, 1997;Mink et al, 1997;OelgeschlaÈ ger et al, 1996). This suggests that the coactivators are involved in mediating the transactivation activity of Myb and C/EBPb.…”

p300 functions as a transcriptional coactivator for the TAL1/SCL oncoprotein

“…They have a recognized function as transcriptional coactivators for diverse families of transcription factors, including the nuclear steroid receptors (Chakravarti et al, 1996;Hanstein et al, 1996;Kamei et al, 1996;Yao et al, 1996), and bHLH Mutoh et al, 1998;Qiu et al, 1998;Sartorelli et al, 1997;Yuan et al, 1996), leucine zipper (Bannister and Kouzarides, 1995;Bannister et al, 1995;Chrivia et al, 1993;Mink et al, 1997), and zinc ®nger (Blobel et al, 1998;Lee et al, 1995) proteins. Acting as transcriptional adaptors, they link sequence-speci®c DNA-binding proteins to components of the basal transcriptional machinery (Abraham et al, 1993;Kee et al, 1996;Nakajima et al, 1997) and to proteins with histone acetyltransferase activity (Yang et al, 1996).…”