Transactivation and DNA binding activity of mutant p53.
Item
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Title
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Transactivation and DNA binding activity of mutant p53.
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Identifier
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AAI9997080
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identifier
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9997080
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Creator
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Chicas, Agustin.
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Contributor
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Adviser: Jill Bargonetti
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Date
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2001
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Molecular | Biology, Genetics
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Abstract
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p53 is the most commonly mutated tumor suppressor gene in human tumors. Mutants of p53 found in tumors have the peculiarity of not only losing the tumor suppressor activity but of also acquiring new growth promoting functions. It has been postulated that the growth promoting activity of mutants of p53 is due to the ability of these mutants to activate transcription of many growth promoting genes (Roemer, 1999). The mechanism of transactivation by the tumor derived mutants of p53, however, remains unclear. Unlike wild-type p53 which is a gene specific transactivator (Oren, 1999), mutants of p53 are generally defective in sequence specific DNA binding (Zambetti, 1993). Although some p53 mutants can bind to DNA albeit different than the wild type protein (Di Cuomo, 1998; Kem, 1991; Park, 1994; Niewolik, 1995), none of the mutants have been shown to bind to any of the genes that are transactivated by mutant p53.;We have used the HIV-LTR to study the mechanism of mutant p53 transactivation as this is one of the promoters that is transactivated by mutants of p53 (Subler, 1994b). Deletion analysis of the HIV-LTR have revealed that the three Sp1 binding sites of the HIV-LTR are important for mutant p53 transactivation (Subler, 1994). We have previously shown that purified mutant p53 does not bind to these three Sp1 binding sites (Bargonetti, 1997). Since Sp1 has been shown to associate with other transcription factor to activate transcription (Kardassis, 1999), we proposed and tested a model whereby mutants of p53 activate transcription by associating with DNA bound Sp1 (Fig. 1.1). Using DNA affinity chromatography, we showed that mutant p53 His 273 in the MDA 468 cells formed a complex with Sp1 on HIV-LTR DNA. This complex, which is not detected by co-immunoprecipitation, is also formed on the p53 super consensus sequence (SCS). We showed that this endogenously expressed mutant p53 his 273, like transfected mutant p53, can activate HIV-LTR driven transcription (Chapter, 3). These data are consistent with our model. Together with previous results, these data suggest that the gain of function activity of mutant p53 may come from the ability of mutant p53 to associate with DNA bound Sp1. This association could lead to an increase in the expression of genes containing Sp1 binding sites. Interestingly, Sp1 binding sites are commonly found in housekeeping and growth promoting genes (Naar, 1998).
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
