Critical transcriptional activator

Trauner, M., Arrese, M., Lee, H., Boyer, J.L. and Karpen, S.J. (1998) Endotoxin downregulates rat hepatic ntcp gene expression via decreased activity of critical transcription factors. Journal of Clinical Investigation, 101, 2092-2100. 

As expected, in vitro transcription assays involving PARP-1, NAD, and PARC illustrate these predicted outcomes (Kim et al, 2004). Even when driven by a transcriptional activator, such as estradiol-bound estrogen receptor, transcription is repressed when PARP-1 is added to chromatin templates. The repression is reversed by NAD+, and the NAD+-dependent effects are reversed by PARC (Kim et al, 2004). This system for transcriptional control shifts new importance onto the enzymes responsible for synthesis of NAD+ in the nucleus, such as nicotinamide mononucleotide adenylyltransferase-1 (Magni et al, 2004). Because NAD+ facilitates the decompaction of chromatin and the derepression of transcription, nuclear NAD+ biosynthetic enzymes may play critical roles as cofactors. 

The ubiquitous transcription factor Spl is critical for both basal and Tat-induced transcription of the HIV-1 LTR (Kamine and Chinnadurai, 1992 Sune and Garcia-Bianco, 1995 Yedavalli et al, 2003). Spl could also play an important role in nuc-1-dependent HIV-1 regulation. Indeed, Spl has been demonstrated to interact with the acetyltransferase p300 and to act as a co-activator for Spl-mediated transcriptional activation (Billon et al, 1999 Suzuki et al, 2000 Xiao et al, 2000). Spl... 

An example of this class of peptide is the 86-amino acid truKi-activating transcriptional activator (TAT) of HIV-1 (74,75). Following incubation with cultured cells, TAT protein is internalized and subsequently transactivates viral promoters (75). The protein has multiple facets invasion, nuclear trophism, and DNA binding (76-81). An invasion domain of TAT has been identified within amino acids 37 to 72 with the critical basic region from amino acids (49 to 57), also known as the minimal transduction domain, which consists of the sequence -Arg-Lys-Lys-Arg-Arg-Gln-Arg-Arg-Arg-. Any deletion in the sequence caused a reduction in translocating activity (82-84). Other prominent CPPs are reviewed in References 73 and 85. 

Each stage described above involves at least one critical RNA-RNA and/or RNA-protein interaction. Initiation of reverse transcription involves the binding of a specific tRNA, which is packaged in the viral particle, to a short sequence of the viral RNA. Transcription and accumulation of viral RNA is dependent upon the sequence-specific interaction between two essential viral regulatory proteins. Tat and Rev, with their respective RNA sites, TAR and RRE (Figure 10.1). Tat is a transcriptional activator, whereas Rev acts post-transcriptionally to increase the cytoplasmic accumulation of the viral gag-pol and env messenger RNAs. Viral assembly is initiated by formation of an RNA-RNA dimer where... 

Apopa PL, He X, Ma Q. 2008. Phosphorylation of Nrf2 in the transcription activation domain by casein kinase 2 (CK2) is critical for the nuclear translocation and transcription activation function of Nrf2 in IMR-32 neuroblastoma cells. J Biochem Mol Toxicol 22 63-76. 

In order to define the limits of the ARE and the bases critical for binding of the protein and for transcriptional activity, the ARE sequence was subjected to a mutational analysis. Mutations were introduced into the ARE using mutant oligonucleotides and these mutant sequences were multimerised to give a four copy ARE promoter. These 4x mutant ARE constructs were assayed for their ability to bind the protein factor or to compete with binding of the wild-type ARE element to the protein. The 4x mutant ARE elements were also linked to the GUS reporter gene and introduced into protoplasts by electroporation to determine their activity as transcriptional effectors under aerobic and anaerobic conditions. 

CREB transcriptional activity is regulated by phosphorylation, and the most critical phosphorylation site is S133 in the KID domain. S133 can be phosphorylated... 

As with other in vivo selections, it is critical to validate hits at the end of the selection experiment with a secondary screen. The most common secondary screen used with the Y2H assay is a lacZ screen. If either the DBD or AD fusion is under control of an inducible promoter, this screen can be carried out both under inducing and non-inducing conditions to ensure that transcription activation is protein dependent. Y3H systems, where transcription activation depends on a bridging RNA or small molecule, and reverse Y2H systems, where a third protein is disrupting the interaction, provide a built-in control. One can simply check that transcription activation is in fact dependent on the third component. As with any in vivo selection, the evolved plasmid should be isolated and retransformed into a fresh yeast selection strain to ensure that the phenotype is plasmid-dependent. Ultimately, the interaction will be confirmed with co-immunoprecipitation experiments or other in vitro binding assays [39]. 

Most transcriptional activators are cytosolic proteins. Therefore, transport to the nucleus and export from the nucleus are points of transcriptional control in cells. Moreover, the time a transcriptional protein resides in the nucleus is a critical factor in the regulation of gene transcription. 

ERa serves as an example of a TF that is dependent on an HDAC for its activity (84). The reduction in expression of this nuclear receptor is a key step in the carcinogenesis of breast cancer and correlates with poor prognosis. ERa has been shown to bind HDACl directly in vitro and in vivo, and the overexpression of HDACl in MCF-7 cells leads to a reduction in both ERa protein levels and ERa transcriptional activity. Overexpression of HDACl also causes increased cell proliferation of MCE-7 cells (96). Thus, it has been suggested that HDACl plays a critical role in breast cancer progression. Consistent with this... 

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