Specificity protein 1 transcription

Chintharlapalli S, Papineni S, Ramaiah SK, Safe S. (2(X)7) Betuhnic acid inhibits prostate cancer growth through inhibition of specificity protein transcription factors. Cancer Res 67 2816-2823. 

The structure of eukaryotic promoters is more complex than that of prokaryotic promoters. DNA sequences, hundreds of base pairs (bp) upstream from the transcription start site, control the rate of initiation. Furthermore, initiation requires numerous specific proteins (transcription factors) that bind to particular DNA sequences. Without the transcription factors, RNA polymerase II cannot bind to a promoter. However, KNH polymerase II itself is not a transcription factor. The complexity of initiation may derive, in part, from the fact that eukaryotic DNA is in the form of chromatin, which is inaccessible to RNA polymerases. Many RNA polymerase II promoters have the following features ... 

Thyroid transcription factor-1 (TTF-1), a nuclear tissue-specific protein transcription factor, is found in thyroid and thyroid tumors regardless of histologic type (except anaplastic type), as well as in lung carcinomas including adenocarcinomas (75%), non-small cell carcinomas (63%), neuroendocrine and small cell carcinomas (>90%), and squamous cell carcinomas (10%).258-258 Selectively expressed during embryogenesis in the thyroid, the diencephalon of the brain, and in respiratory epithelium, TTF-1 binds to and activates factors for surfactant protein derived from Clara cells.255 TTF-1 is rarely seen in carcinomas outside of the lung or thyroid... 

By selectively affecting gene transcription and the consequent production of appropriate target mRNAs, the amounts of specific proteins are changed and metabolic processes are influenced. The influence of each of these hormones is quite specific generally, the hormone affects less than 1% of the genes, mRNA, or proteins in a target cell sometimes only a few are affected. The nuclear actions of steroid, thyroid, and retinoid hormones are quite well defined. Most evidence sug-... 

In Drosophila the two tissue-specific mRNAs are generated by alternative splicing of a single primary transcript (Fig. 9). In vertebrates the two tissue specific AADC transcripts are generated from two alternative promoters (Fig. 11) (Albert et al., 1992 Ichinose et al., 1992 Thai et al., 1993). In neural tissue transcription initiates from exon Nl, whereas in non-neural tissue transcription initiates from exon LI. This produces two distinct primary transcripts that are then spliced from the first exon (LI or Nl) to exon 2 to generate two tissue-specific mRNAs. Translation initiates within exon 2, such that the same AADC protein product is synthesized from both AADC mRNAs. 

An additional sequence element within the mouse ZP3 promoter has been identified as the binding site of an oocyte-specific protein called OSP-1 (Schickler et al., 1992), although the possible effect of mutations of this element on transcriptional activity has not been established. Nonetheless, it is interesting that a similar sequence (GATGA) is present 40 nucleotides upstream of the c-mos transcription initiation site (Fig. 5), although deletion of this element had no discernible effect on the activity of the c-mos promoter in microinjected oocytes (Pal et al., 1991). 

One way to control how much of something a cell uses or makes is to control the levels of the enzymes that are required to metabolize it (Fig. 5-7). Whether or not transcription happens is controlled by the binding of specific proteins to the DNA. When they bind to DNA, these proteins can either help or hinder the transcription process. Positive and negative refer only to the effect a protein has when it binds to the DNA. A positive effect is when the protein binds to the DNA and turns on the transcription of the gene. A negative effect is when the binding of the protein to the DNA turns off transcription. 

The cellular mechanism of action of hydrocortisone, a glucocorticoid, is also related to proteins but not by the enhancement of cAMP production. Hydrocortisone is transported by simple diffusion across the membrane of the cell into the cytoplasm and binds to a specific receptor The steroid-receptor complex is activated and enters the nucleus, where it regulates transcription of specific gene sequences into ribonucleic acid (RNA). Eventually, messenger RNA (mRNA) is translated to form specific proteins in the cytoplasm that are involved in the steroid-induced cellular response. 

Ligand-bound corticosteroid receptors have been shown to interact to form heterodimers with other transcription factors, such as the jun protein. Such interactions are responsible for transactivation of the ds-regulatory sites known as AP-1 sites and for the glucocorticoid-mediated suppression of transcription, such as that seen in the pro-opiomelanocortin gene. A number of such specific protein interactions have been reported these interactions and their locations relative to other transcription factors transform a ubiquitous steroid hormone signal into a tissue-specific, graded cellular response. 

Adenylate cyclase was identified as the primary Ras target in yeast (Saccha-romyces cerevisiae) [56] but it took a while before in 1993 several groups independently found Raf to be the effector of Ras in mammals [41-44]. Shortly afterwards it was realized that this is not the only target of Ras but up until now it appears to be the most prominent one. Raf is a Ser/Thr-specific protein kinase which phosphorylates and thereby activates Mek which in turn phosphorylates and activates Erk, leading to an amplification of the signal. Erk, also termed MAPK, has a plethora of phosphorylation targets, the most important of which are transcription factors such as Elk-1, leading to activation of the transcription machinery in the nucleus. 

Acridinium ester—labeled chemiluminescent probes have been utilized to detect the specific protein-coding transcripts and to distinguish between transcripts that code for the 190-kDa protein and the two closely related 210-kDa proteins. The assay is called the hybridization protection assay (D3). In this assay, RNA isolated from the patient s white blood cells is first amplified by PCR. The amplified product is incubated with the chemiluminescent probe. The unhybridized probe is removed by selective hydrolysis in sodium tetraborate buffer, containing surfactant Triton X-100 at pH 8.5, in an incubation step at 60°C for 6 min. After the sample is cooled to room temperature, the chemiluminescence of the hybridized probe is measured in a luminometer. The procedure is reported to detect one leukemic cell in a population of a million or more normal cells. It is also rapid, requiring less than 30 min. Its reliability has been attested to by correlation with results obtained on karyotypic and Southern blot analysis (D3). 

Figure 12.8 Effector mechanism activation of a specific gene by hormone-receptor complex binding to DNA. A steroid is used to illustrate the mechanism. The hormone enters the cell and binds to its receptor (R) in the cytosol, the hormone-receptor complex enters the nucleus and binds to a specific sequence in the DNA that stimulates transcription of a gene or genes the resultant increase in mRNA increases the synthesis of specific proteins. The binding site on the DNA is specific and is usually termed a response element. Thyroxine (i.e. triiodothyronine) also uses this effector mechanism. Activation of genes, RNA processing to produce mRNA and translation are described in Chapter 20 (see Figures 20.20, 20.21 and 20.22).

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