Investigation of Gain-of-Function Induced by Mutant p53

• Main Author: Vaughan, Catherine
• Format: Others
• Published: VCU Scholars Compass 2015
• Subjects: p53; NFkB2; Axl; EGFR; transcription; gain-of-function; Cancer Biology
• Online Access: http://scholarscompass.vcu.edu/etd/3965; http://scholarscompass.vcu.edu/cgi/viewcontent.cgi?article=5001&context=etd

p53 is mutated in 50% of all human cancers, and up to 70% of lung cancer. Mutant p53 is usually expressed at elevated levels in cancer cells and has been correlated with a poor prognosis. Cancer cells that express mutant p53 show an increase in oncogenic phenotypes including an increase in growth rate, resistance to chemotherapeutic drugs, and an increase in motility and tumorigenicity to name a few. We have identified several genes involved in cell growth and survival that are upregulated by expression of common p53 mutants: NFκB2, Axl, and epidermal growth factor receptor (EGFR). The aim of this study was to determine the role NFκB2, Axl, and EGFR play in mutant p53’s gain of function (GOF) phenotype and to determine a mechanism for upregulation of mutant p53 target gene upregulation. Inhibition of mutant p53 in various cancer cell lines using RNAi in the form of transient siRNA transfection or stable shRNA cell line generation caused a decrease in the gain of function ability of those cells in the form of reduced chemoresistance, reduced cell growth and motility, and a reduction in tumor formation. Additionally, inhibition of NFκB2, Axl, and EGFR also showed similar effects. Promoter deletion analysis of the NFκB2 promoter did not show a specific mutant p53 response element needed for mutant p53 mediated transactivation. Similarly, deletion of the p53/p63 binding site on the Axl promoter did not inhibit mutant p53 transactivation. Sequence analysis of the NFκB2, Axl, and EGFR promoters revealed several transcription factor binding sites located throughout the promoters. ChIP analysis of mutant p53 and the promoter-specific transcription factor binding revealed that in the presence of mutant p53, individual transcription factor binding is increased to the NFκB2, Axl, and EGFR promoters as well as an increase in acetylated histone binding. This data suggests that mutant p53 promotes an increase in transcription by inducing acetylation of histones via recruitment of transcription factors to the promoters of mutant p53 target genes.