Histone acetyltransferase activity

Coactivators enhancing the transcriptional activity of steroid hormone receptors activators include SRC-1 (steroid-receptor co-activator 1) or TEF2 (transcriptional intermediary factor 2), which are recruited by the DNA/ steroid hormone receptor complex. Their main role is to attract other transcriptional coactivators with histone acetyltransferase activity in order to decondense chromatin and allow for the binding of components of the general transcription apparatus. 

Despite the complexity of the experiments and the enormous data manipulation necessary, complex biological pathways, as well as new drug targets are being identified by this method. Examples include screens for compounds that arrest cells in mitosis, that block cell migration, and that block the secretory pathway [50], or assays with primary T cells from PLP TCR transgenic mice for their inhibitory activity on the proliferation and secretion of proinflammatory cytokines in PLP-reactive T cells [51], and identification of small-molecule inhibitors of histone acetyltransferase activity [52]. 

The structure of the chromatin and their state of acetylation are important at the moment of initiating the gene transcription. Indeed, some of the transcription factors recruited by the receptor dimer have histone-acetyltransferase activity that permits the gene transcription after diminishing the condensation of the chromatin (Gruber et al. 2002 Nilsson et al. 2001 Vigushin et al. 2002). 

Creaven M, Hans F, Mutskov V, Col E, Caron C, Dimitrov S, Khochbin S (1999) Control of the histone-acetyltransferase activity of Tip60 by the HIV-1 transactivator protein, Tat. Biochemistry 38 8826-8830... 

Nair AR, Boersma LJ, Schilz L, Chaudhry MA, Muschel RJ, Chaudry A. (2001) Paradoxical effects of trichostatin A Inhibition of NE-Y-associated histone acetyltransferase activity, phosphorylation of hGCN5 and down-regulation of cyclin A and B1 mRNA. Cancer Lett 166 55-64. 

Traditionally, HAT activity is measured with a discontinuous radioactive filterbinding assay, which uses pH]acetyl-CoA as a histone acetyltransferase substrate [46]. The transfer of [ H]acetyl-groups to the histone substrate by histone acetyltransferases is detected by liquid scintillation counting of pHjacetylated histones, which are retained on a phosphocellulose disk. Due to its discontinuous character, this assay is technically problematic and not ideal for kinetic analysis. Hence, other assays that work with radiolabeled acetyl-CoA have been described that are suitable for a higher throughput. These work with streptavidin-covered beads [47] or a variant of the SPA with microtiter plates that contain a scintillant (FlashPlates) [48]. But as all these protocols are based on radioactively labeled substrates, they apparently show the same disadvantages that were described for the radioactive HDAC assay protocols. Therefore, nonradioactive assays have been developed to study histone acetyltransferase activity. 

Ait-Si-Ali, S., Ramirez, S., Robin, P., Trouche, D. and Harel Bellan, A. (1998) A rapid and sensitive assay for histone acetyltransferase activity. Nucleic Acids Research, 26. 3869-3870. 

Thompson, P.R., Kurooka, H., Nakatani, Y. and Cole, P.A. (2001) Transcriptional coactivator protein p300. Kinetic characterization of its histone acetyltransferase activity. The Journal of Biological Chemistry, 276, 33721-33729. 

Sun, Y.L., Jiang, X.F., Chen, S.J. and Price, B.D. (2006) Inhibition of histone acetyltransferase activity by anacardic acid sensitizes tumor cells to ionizing radiation. FEBS Letters, 580, 4353 356. 

Stimson, L., Rowlands, M.G., Newbatt, Y.M., Smith, N.F., Raynaud, F.I., Rogers, P. et al. (2005) Isothiazolones as inhibitors of PCAF and p300 histone acetyltransferase activity. Molecular Cancer Therapeutics, 4, 1521—1532. 

Gcn5 A yeast transcriptional adaptor that has histone acetyltransferase activity... 

Transcription intermediary factor 2, a transcriptional coregulatory protein which contains several nuclear receptor interacting domains and an intrinsic histone acetyltransferase activity... 

Korzus E, Rosenfeld MG, Mayford M (2004) CBP histone acetyltransferase activity is a critical component of memory consolidation. Neuron 42(6) 961-972... 

Shen, W.F., Krishnan, K., Lawrence, H.J., Largman, C. 2001. The HOX homeodomain proteins block CBP histone acetyltransferase activity. Mol. Cell Biol. 21, 7509-7522. 

In a search for a factor that could enable a response to transcriptional activators in a pure in vitro transcription system, R. D. Kornberg and colleagues isolated an activity from. S , cerevisiae that was termed Mediator (Flanagan et al., 1991 Kelleher et al., 1990). The assay used was based on naked DNA templates and thus reflects the second stage of the transcription initiation process described above. The Mediator activity was purified to homogeneity and shown to be a holoenzyme form of RNA Pol II, made up of core 12-subunit RNA Pol II and a Mediator complex (Kim et al., 1994). Mediator was later also isolated as a discrete entity and identified as a multiprotein complex of 20 individual polypeptides (Table I Myers et al., 1998). The functional activities identified for the Mediator were stimulation of basal transcription, support of activated transcription, and enhancement of phosphorylation of RNA Pol II by TFIIH kinase (Kim et al., 1994 Myers et al., 1998). Later studies also identified a histone acetyltransferase activity in the S. cerevisiae Mediator (Lorch et al., 2000). 

Loewith, R., Meijer, M., Lees-Miller, S. P., Riabowol, K., and Young, D. (2000). Three yeast proteins related to the human candidate tumor suppressor pSS are associated with histone acetyltransferase activities. Mol. Cell. Biol. 20, 3807-3816. 

Recently, other transcriptional coactivators harboring histone acetyltransferase activity, namely SRC-1/pi60, were demonstrated to enhance hypoxic stimulation (74). This complex also includes the bifunctional Ref-1 protein (74). These protein factors seem to act synergisticaUy with CBP. 

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