RbBP6 Isoform 3 (DWNN) is a p53 stabilizer in arsenic trioxide-induced apoptosis in human cancer cell lines. Zodwa Dlamini. 1. , Zukile Mbita. 2. , Amanda ...
RbBP6 Isoform 3 (DWNN) is a p53 stabilizer in arsenic trioxide-induced apoptosis in human cancer cell lines 1
Author Affiliations 1 Univ. of Limpopo, Sovenga, South Africa 2 Univ. of the Western Cape, Bellville, Cape Town, South Africa. Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC
Abstract Domain With No Name (DWNN) has a ubiquitin-like fold and shares 22% similarity with ubiquitin. This suggests its significant importance in cell homeostasis and protein degradation in a human body. The presence of a ubiquitin-like fold suggests a role similar to ubiquitin and RbBP6 may be involved in ubiquitin ligase-like activities. Furthermore RbBP6 interacts with both p53 and pRb which are key components of cell cycle regulation. These two tumour suppressors are key to the understanding the function of the RbBP6. It has been found that upon arsenic trioxide-induced treatment RbBP6 isoform 3 (DWNN) is upregulated. In this study the role of the DWNN on p53-dependent apoptosis was investigated. Over-expressions of RbBP6 isoforms was achieved by transfection of recombinant isoforms using Metafectene Easy. Apoptosis was induced using arsenic trioxide and staurosporine. Apoptosis was then measured using APOPercentage and flow cytometry. The expression of RbBP6 gene products and p53 was determined using both real-time PCR and western blotting. Up-regulation of RbBP6 was observed in As2O3-induced apoptosis in cancer cells. Over-expression of the RbBP6 isoform 1 intensified As2O3induced apoptosis. MTT assay showed an IC50 of 40µM for As2O3. When this concentration was used to induce apoptosis in human cancer cells and this resulted in induced expression of RbBP6 isoform 1 not the isoform 3. Over-expression of RbBP6 isoform 3 though resulted in stabilization of p53 protein. The apoptosis that was observed was also accompanied by the expression of p53. This study suggests that the DWNN may not be directly involved in the prosecution of apoptosis but may be involved through p53 stabilization. This study suggests that the RbBP6 may be a p53 stabilizer in contrast to mdm2, which is a negative regulator of p53. It will be very important to also determine the relationship between RbBP6 and pRb in both cell cycle and apoptosis
