Abstract 1085: RbBP6 isoform 3/DWNN is essential for arsenic trioxide-induced G2/M arrest in cancer cell lines
Authors: Mbita Zukile , Skepu Amanda , Pugh David , Rees Jasper , Dlamini Zodwa , Meyer Mervin 
Published: February 2011

Abstract
Retinoblastoma binding protein 6 (RbBP6) is a gene that encodes RbBP6 protein products (isoforms 1,2 and 3) that has previously been documented to bind retinoblastoma protein (pRb) and p53, which are key components of cell cycle regulation and localises on chromosome 16p12.2 in humans. These isoforms are derived from two major mRNA transcripts, a 1.1 kb (Isoform 3) and 6.1 kb (isoform 1and 2). These two tumour suppressors are important to the understanding the function of the RbBP6. Arsenic trioxide has been used to treat APLS and has been shown to arrest cells at G1 and G2. In this study, the involvement of the DWNN in cell cycle arrest caused by As2O3 was investigated.
RNA interference was employed to investigate the involvement of the DWNN in cell cycle regulation. Immunocytochemistry was employed to determine the localization of the DWNN-containing proteins in human cancer cells as well as non-cancerous cells. Propidium iodide cell cycle analysis was used to quantify cell cycle arrest induced by As2O3. Western blotting and real-time PCR were used to determine the expression of the DWNN in both control and treated cells.
RNA interference was employed to investigate the involvement of the DWNN in cell cycle regulation. Immunocytochemistry was employed to determine the localization of the DWNN-containing proteins in human cancer cells as well as non-cancerous cells. Propidium iodide cell cycle analysis was utilised to quantify cell cycle arrest induced by As2O3. Western blotting and real-time PCR were used to determine the expression of the DWNN in both control and treated cells.
DWNN knockdown increased cell proliferation and did not have an effect on apoptosis. Treatment of human cells with low concentrations of As2O3 induced G2 cell cycle arrest and resulted in induced expression of DWNN. This induced cell cycle arrest was also associated with deglycosylation of the DWNN domain. This finding is in line with the localization of the DWNN proteins in human cancer cells, which showed high expression of the DWNN proteins in G2/M cell cycle phase. Expression analysis showed that the up-regulation of the DWNN domain resulted in p53 up-regulation.
These results strongly suggest that the DWNN may be either required for G2 cell cycle arrest or may be required for p53 stabilization during this phase or may be needed for signalling for progression to the next phase of cell cycle. DWNN involvement in cell cycle may be in a p53-dependent manner. Staurosporine which induces G1 cell cycle arrest did not result in DWNN up-regulation and that suggest that DWNN may not be required for G1 cell cycle arrest or regulation. The effect of DWNN in pRb phosphorylation and G1 cell cycle arrest still needs more attention.
Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1085.