Histone chaperones assemble and disassemble nucleosomes in an ATP-independent manner and thus regulate the most fundamental step in the alteration of chromatin structure. The molecular mechanisms underlying histone chaperone activity remain unclear. To gain insights into these mechanisms, we solved the crystal struc

Here we show a novel pathway of transcriptional regulation of a DNA-binding transcription factor by coupled interaction and modification (e.g., acetylation) through the DNA-binding domain (DBD). The oncogenic regulator SET was isolated by affinity purification of factors interacting with the DBD of the cardiovascular transcription factor KLF5. SET negatively regulated KLF5 DNA binding, transactivation, and cellproliferative activities. Down-regulation of the negative regulator SET was seen in response to KLF5-mediated gene activation. The coactivator/acetylase p300, on the other hand, interacted with and acetylated KLF5 DBD, and activated its transcription. Interestingly, SET inhibited KLF5 acetylation, and a nonacetylated mutant of KLF5 showed reduced transcriptional activation and cell growth complementary to the actions of SET. These findings suggest a new pathway for regulation of a DNA-binding transcription factor on the DBD through interaction and coupled acetylation by two opposing regulatory factors of a coactivator/acetylase and a negative cofactor harboring activity to inhibit acetylation.The Sp/KLF (for Sp1-and Krüppel-like factor) family of zinc finger transcription factors has received recent attention due to important roles in developmental, differentiation, and oncogenic processes, among others (2, 3,35). It is comprised of over 15 mammalian family members which have in common three similar C 2 H 2 -type zinc fingers at the carboxyl terminus which comprises the DNA-binding domain (DBD). Sp/KLF family members include the founding ubiquitous factor Sp1 (9), the erythroid differentiation factor EKLF/KLF1 (27), and the tumor suppressor gene KLF6/GBF/Zf9/COPEB, which we and others identified as a cellular factor possibly involved in human immunodeficiency virus type 1 transcription (18,32,44). It was recently shown by gene knockout studies that the proto-oncogene KLF5/BTEB2/IKLF (40, 42) is important for cardiovascular remodeling in response to stress (41). Contrary to initial expectations that this family of factors would likely have redundant functions, they in fact have important individual biological functions. However, the underlying mechanisms governing their specific functions and regulation are poorly understood.We have studied the regulatory mechanisms of action of Sp/KLF family members in the past and have shown differential regulation through interaction and acetylation on the DBD by the coactivator/acetylase p300 (45). Acetylation is an important nuclear regulatory signal which regulates transcriptional processes with biological implications, including regulation of development, differentiation, and oncogenesis (5, 10, 31), which closely resembles the roles of Sp/KLF family members. We therefore thought that the Sp/KLF factors may be differently regulated by acetylation and showed that the coactivator/acetylase p300, but not the MYST-type acetylase Tip60, specifically interacts and acetylates Sp1 but not KLF6 through the zinc finger DBD and that DNA binding inhibits this interaction and ace...

Eukaryotic DNA is packaged into chromatin by histone proteins, which assemble the DNA into an organized, higher-order structure. The precise organization of chromatin is essential for faithful execution of DNA-mediated reactions such as transcription, DNA replication, DNA repair and DNA recombination. The organization of chromatin is considered to be regulated by a variety of post-translational modifications of histones, such as acetylation, methylation, phosphorylation, ubiquitination, SUMOylation and poly-ADP-ribosylation. The relationship between histone acetylation and gene expression was first observed in 1964. Since then, a great deal of evidence has accumulated showing that not only transcription but other DNA-mediated reactions also are regulated by histone acetylation. With regard to the putative mechanism(s) by which histone acetylation regulates the flow of genetic information, site-specific modification and recognition of acetylated histone/DNA complexes have been postulated. Elucidation of the downstream effects of histone modification, as well as the identification, isolation and characterization of the relevant factors involved, have aided in our understanding of the mechanisms of regulation of DNA activity by histones. Currently, state-of-the-art technologies that enable genome-wide analysis are allowing insight into a critical and interesting question in eukaryotic transcription: are the principles that govern transcription of individual gene loci applicable to the genome as a whole? Here, we review the recent progress on histone modifications, with an emphasis on the role of histone acetylation in gene expression.

Transcription is regulated by a network of transcription factors and related cofactors that act in concert with the general transcription machinery. Elucidating their underlying interactions is important for understanding the mechanisms regulating transcription. Recently, we have shown that Krü ppel-like factor KLF5, a member of the Sp/KLF family of zinc finger factors and a key regulator of cardiovascular remodeling, is regulated positively by the acetylase p300 and negatively by the oncogenic regulator SET through coupled interaction and regulation of acetylation. Here, we have shown that the deacetylase HDAC1 can negatively regulate KLF5 through direct interaction. KLF5 interacts with HDAC1 in the cell and in vitro. Gel shift DNA binding assay showed that their interaction inhibits the DNA binding activity of KLF5, suggesting a property of HDAC1 to directly affect the DNA binding affinity of a transcription factor. Reporter assay also revealed that HDAC1 suppresses KLF5-dependent promoter activation. Additionally, overexpression of HDAC1 suppressed KLF5-dependent activation of its endogenous downstream gene, platelet-derived growth factor-A chain gene, when activated by phorbol ester. Further, HDAC1 binds to the first zinc finger of KLF5, which is the same region where p300 interacts with KLF5 and, intriguingly, HDAC1 inhibits binding of p300 to KLF5. Direct competitive interaction between acetylase and deacetylase has been hitherto unknown. Collectively, the transcription factor KLF5 is negatively regulated by the deacetylase HDAC1 through direct effects on its activities (DNA binding activity, promoter activation) and further through inhibition of interaction with p300. These findings suggest a novel role and mechanism for regulation of transcription by deacetylase.Transcription is regulated by a network of regulatory transcription factors and coregulatory proteins (cofactors) that collectively act in concert with the general transcription machinery (1-5). Cofactors, as coactivators or corepressors, exert their activities in main through protein-protein interaction and/or chemical modification (e.g. phosphorylation, acetylation), thus allowing for noncatalytic and/or catalytic regulatory processes. Understanding the molecular mechanisms underlying transcriptional regulation, especially with a focus on protein-protein interaction with coupled chemical modification, is a recent topic of interest.Acetylation is a chemical modification that is linked to transcription and is regulated in main by the catalytic enzymes, acetylase and deacetylase. Recent research has identified the factors bearing acetylase activity (e.g. p300, p300/ CREB-binding protein-associated factor) as well as deacetylase activity (HDACs) and their catalytic roles in transcriptional regulation (6 -10). We have, however, shown that the acetylase p300 not only regulates a DNA binding transcription factor, Sp1, by catalytic means (acetylation) but also that its effects are importantly, as well as unexpectedly, mediated by direct noncatalytic ef...