Abstract 4308: RBBP6 expressional effects on cell proliferation and apoptosis in breast cancer cell lines with distinct p53 statuses

Abstract

Abstract Breast cancer incidence rate has increased beyond that of lung cancer, making it the most common malignancy among women. Breast tumour progression is partly as a result of p53 inactivation by overexpressed ubiquitous regulatory proteins that possess p53 binding domain. RBBP6 forms a member of such protein since it has an E3 ligase activity due to its RING finger-like domain. Moreover, its overexpression in several malignancies makes it a potential target in cancer management. However, it is not clearly defined whether RBBP6 effect on cell growth and apoptosis is cell line dependent, more especially in breast cancer cell lines that have distinct p53 expression profiles. The present study therefore aims at evaluating RBBP6 effects on cell growth and apoptosis in breast cancer cell lines with different p53 expression profiles. Following analysis at mRNA and protein levels in breast cancer tissue, RBBP6 expression was successfully manipulated using gene silencing and protein overexpression techniques in MCF-7 and MDA-MB-231 cell lines. Transfection efficiencies were confirmed using qPCR and western blot, followed by monitoring of cell proliferation in the presence of transfection using xCELLigence system. The cells were then co-treated with anti-cancer agents followed by apoptosis detection using confocal microscopy and flow cytometry, which was further confirmed by caspase 3/7 activity and quantification of apoptotic genes. RBBP6 was overexpressed in breast cancer tissues that were classified as stage 3 and 4 while in stage 1 it was expressed but at much lower levels. The wt. p53-expressing MCF-7 cell line was more susceptible to apoptosis induction as opposed to the mt. p53-expressing MDA-MB-231. RBBP6 silencing led to a significant accumulation of p53 expression in MCF-7 as compared to MDA-MB-231. Co-treatment with GABA and camptothecin seemed to sensitize the cells to apoptosis induction. These data suggest that RBBP6 silencing triggers significant levels of intrinsic apoptosis and over-expression appears to promote cell proliferation in wild type p53-expressing MCF-7 rather than in MDA-MB-231 cells. Insignificant changes in the expression of mt. TP53 in MDA-MB-231 cell line following RBBP6 silencing and over-expression suggests that RBBP6 is highly likely to interact with wt-p53 rather than mutated p53. In conclusion, the effect of RBBP6 on cell proliferation and apoptosis induction in breast cancer seem to be cell line dependent based on p53 status Citation Format: lesetja R. Motadi, pontsho Moela. RBBP6 expressional effects on cell proliferation and apoptosis in breast cancer cell lines with distinct p53 statuses [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4308.