Upstream stimulating factor

Fig. 2. Regulation of thymidylate synthase (TS) gene expression. Abbreviations.- TS (thymidylate synthase) USF-1 (upstream stimulating factor 1) USF-2 (upstream stimulating factor 2) SNP (single nucleotide polymorphism). (Reprinted with permission of El-Khoueiry et al. Pharmacogenomics and molecular biology of gastrointestinal cancers, Atlas of Gastrointestinal Cancers, Current Medicine Group, LLC, Philadelphia, 2007).

In a recent study, Mandola et al. showed that the 28 bp TSER tandem repeats contain elements that bind upstream stimulating factor (USF), and also that ligand binding by USF-1 and USF-2 enhances the transcriptional activity of the TS gene (Fig. 2) (42). Electrophoretic mobility shift analysis has shown that the presence of a G-to-C single nucleotide polymorphism (SNP) within the second repeat of the 3R allele leads to decreased ability of upstream stimulatory factor (USF) to bind within the repeat and therefore sequentially result in decreased transcriptional activity of the 3R TS gene variant (42). 

Another example of problems in interpreting results in knockout mice is demonstrated by the following An important role of colony-stimulating factor (CSF) in hemopoiesis of myeloid lineage cells has been demonstrated. G-CSF was knocked out, animals were neutropenic and had decreased hemopoietic progenitors in bone marrow and spleen [24]. In contrast, mice with a null mutation in GM-CSF, which acts upstream to G-CSF in myeloid differentiation, demonstrated no impairment of hemopoiesis, but develop a characteristic pulmonary pathology [25]. Therefore, we have to interpret the results of our experiments with knockout mice with caution. 

A sequence stretch 300 base pairs upstream of the transcriptional start site suffices for most of the transcriptional regulation of the IL-6 gene (Fig. 1). Within this sequence stretch several transcription factors find their specific recognition sites. In 5 to 3 direction, AP-1, CREB, C/EBP 3/NF-IL6, SP-1 and NF-kB can bind to the promoter followed by TATA and its TATA binding protein TBP. Most enhancer factors become active in response to one or several different stimuli and the active factors can trigger transcription individually or in concert. For example, AP-1 is active upon cellular stress, or upon stimuli that tell cells to proliferate CREB becomes also active if cells experience growth signals, but also upon elevation of intracellular levels of cyclic adenosine monophosphate (cAMP), which occurs upon stimulation if so called hormone-activated G protein-coupled receptors. 

The formation of the PIC described above is based on the sequential addition of purified components in in vitro experiments. An essential feature of this model is that the assembly takes place on the DNA template. Accordingly, transcription activators, which have autonomous DNA binding and activation domains (see Chapter 39), are thought to function by stimulating either PIC formation or PIC function. The TAF coactivators are viewed as bridging factors that communicate between the upstream activators, the proteins associated with pol II, or the many other components of TFIID. This view, which assumes that there is stepwise assembly of the PIC—promoted by various interactions between activators, coactivators, and PIC components— is illustrated in panel A of Figure 37-10. This model was supported by observations that many of these proteins could indeed bind to one another in vitro. 

Any DNA sequence that binds protein factors and thereby stimulates transcription. This stimulatory effect may occur over an appreciable distance from the enhancer s site. Enhancers act in either strand orientation, and they can be found either upstream or downstream with respect to the promoter. 

All IFN-stimulated genes are characterized by the upstream presence of an interferon-stimulated response element (ISRE). Signal transduction culminates in the binding of specific regulatory factors to the ISRE, which stimulates RNA polymerase Il-mediated transcription of... 

Enhancer. A DNA sequence that can bind protein factors that stimulate transcription at an appreciable distance from the site where it is located. It acts in either orientation and either upstream or downstream from the promoter. 

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