| Chemotherapeutic treatment of malignancies, including chronic lymphocytic leukemia (CLL), is severely hampered by development of chemoresistance due to dysfunctional p53 . A standardized method to determine p53 functionality does not exist. Novel data point to a role of the p53-homologue p73, in apoptosis (programmed cell death) regulation especially in p53 dysfunctional cancer cells. The p73 locus encodes both a tumor suppressor (TAp73) and a putative oncogene (deltaNp73). Mechanisms that control TA and deltaNp73 activity and protein stability are just now coming into focus and include complex post-translational modifications such as (c-Abl dependent) phosphorylation and ubiquitination. In CLL the knowledge on the role and regulation of p73 is sparse. In preliminary studies, we observed that overexpression of TAp73, either by CD40-stimulation or by adenoviral overexpression, resulted in induction of death receptors, the pro-apoptotic protein Bid and enhanced chemosensitivity, importantly, also in p53-deficient CLL cells. These results indicate that induction of TAp73 can overcome resistance of p53-deficient CLL cells to anti-cancer therapy. Aim+Approach: A.To develop a standardized system to assess p53/p73 gene expression and functionality based on a multiplex assay that measures the expression of the p53/p73 genes and their targets. B1. To study regulation of TAp73 protein expression in CLL. We will elaborate on our previous observations of c-Abl-dependent p73 protein expression following CD40 activation and study transcriptional and post-translational regulation of TAp73 by manipulation of both stress-activated kinases and proteasome degradation. B2. To study the role of TAp73 in apoptosis regulation especially in p53-deficient cells: Following TAp73 overexpression we will study expression of target genes that regulate apoptosis, elucidate a direct (non-transcriptional) role of TAp73 in apoptosis induction, and determine the influence of TAp73 expression on death receptor expression and function. Potential importance:- There is great need for a clinical applicable assay that predicts responses to cancer therapy. A multiplex p53/p73 and apoptosis genes assay could fulfill this purpose. - A thorough understanding of p73 regulation might result in new therapeutic strategies to overcome p53 dysfunction not only in CLL but also in other malignancies. |
