Despite substantial advances in the treatment of childhood acute lymphoblastic leukemia (ALL), approximately 25-35% of children with this disease will relapse or fail induction therapy. Failure to respond to treatment may result from development of resistance to apoptosis induced by chemotherapeutic agents. In the applicant's studies of pediatric ALL in relapse, he has found that leukemic cells expressing a mutant p53 gene or overexpressing the p53-inhibitory MDM2 oncogene express constitutively high levels of activated Nuclear Factor kappa B (NFkB), which has been linked to resistance to apoptosis following DNA damage. Conversely, ALL cells expressing wild type (wt)-p53 typically show either no or very low levels of activated NFkB. Since wt-p53 function is induced in cells following DNA damage, and since this function is lost in cells expressing a mut-p53 allele or overexpressing MDM2, the applicant hypothesizes that an important apoptosis-inducing effect of wt-p53 may be inhibition of NFkB activity. Accordingly, expression of mut-p53 or high levels of MDM2 would increase the level of activated NFkB by suppressing the NFkB-inhibitory function of wt-p53. Thus, in normal cells, p53 and NFkB would mutually interact in response to DNA damage to permit apoptosis in cells sustaining irreparable DNA damage; loss of this mutual regulation by either p53 mutation or MDM2 overexpression would result in resistance to apoptosis-inducing agents. To test his hypothesis, he will study the potential upregulation of NFkB activity by either mutant p53 or MDM2 in ALL cells. Importantly, he will examine the cellular consequences of directly inhibiting MDM2 and NFkB activation. These studies may have direct clinical application in suggesting ways to inhibit NFkB-mediated therapy resistance in leukemia and other malignancies.
The specific aims of this study are 1) To evaluate the ability of mutant p53 and overexpressed MDM2 to activate NFkB by transcriptionally regulating NFkB/p65 gene expression, including identification of possible p53- or MDM2-binding and response elements in the p65/RelA promoter; 2) To investigate the ability of mut-p53 and MDM2 proteins to activate NFkB by enhancing turnover of the NFkB inhibitor IkBa and 3) To evaluate the effect of blocking MDM2 overexpression and augmenting IkB levels on sensitivity to apoptosis utilizing anti-MDM2 antisense and proteasome inhibitors, respectively.
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