Abstract 1246: c-Myc is critical for apoptosis in 4-hyroxynonenal-treated colorectal cancer cells
Authors: Wales Christina TK , Gristock Rachel , So Nadine , Jacobs Aaron T. 
Published: August 2015

Abstract
The transcription factor c-myc has an important role in the control of cell proliferation, differentiation and apoptosis. The dysregulation of c-myc activity is a feature of many cancers. Although it enhances proliferation, the overexpression of c-myc also sensitizes cells to a variety of pro-apoptotic stimuli. 4-hydroxynonenal (HNE) is a reactive lipid that is generated as a consequence of oxidative stress, and is found to be elevated in many solid lesions. HNE is known to promote apoptosis in various cancer cell types, including colorectal cancer cells. We therefore decided to investigate whether c-myc has a role in HNE-induced apoptosis in this setting.
We began by investigating the effect of HNE on c-myc expression and function. Treatment of colorectal cancer cell lines RKO and HCT-116 with HNE caused a time- and concentration-dependent nuclear accumulation of c-myc protein. The increase in nuclear c-myc levels was not accompanied by an increase in either c-myc mRNA or total cellular levels, leading us to speculate that enhanced nuclear import or sequestration are involved. To evaluate whether c-myc activity was also increased in response to HNE, we used a luciferase reporter construct bearing a conserved c-myc binding element. These data reveal that in addition to causing its nuclear accumulation, HNE also enhances c-myc transcriptional activity.
To examine the consequence of c-myc activation and explore its role in HNE-induced apoptosis, we silenced c-myc expression using 3 different siRNA sequences in both the RKO and HCT-116 cell lines. Silencing c-myc expression caused a significant attenuation of apoptosis in HNE-treated cells, as evidenced by a reduction in caspase 3 cleavage, PARP cleavage, and caspase 3 activity assays. To investigate the reason behind this effect, we examined known pathways for HNE-induced apoptosis. In accordance with published data, we find that HNE promotes apoptosis through the ASK1-JNK pathway, and that apoptosis can be blocked with an ASK1-specific inhibitor. Furthermore, our data show for the first time that silencing c-myc expression leads to a profound reduction in the phosphorylation and activity of JNK, which we propose explains the reduction in apoptosis in c-myc deficient cells.
Since c-myc is a protein of interest and potential target for colorectal therapy, the consequence of its inhibition on cancer cell viability and cell death pathways is critical to understand. Together, our work reveals a novel pathway for c-myc mediated apoptosis and highlights its importance in HNE-treated cancer cells.
Citation Format: Christina TK Wales, Rachel Gristock, Nadine So, Aaron T. Jacobs. c-Myc is critical for apoptosis in 4-hyroxynonenal-treated colorectal cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1246. doi:10.1158/1538-7445.AM2015-1246