Abstract 1114: Loss of OPA1 expression results in apoptosis for cells overexpressing c-Myc

Abstract

Listen

Translate article

Abstract c-Myc (Myc) is a transcription factor that controls the expression of a vast array of genes that function in many essential cellular pathways, and high levels of Myc have been implicated in the development of many human cancers. One pathway that Myc controls is mitochondrial biogenesis. We have previously shown that Myc does this is in part via the regulation of the expression of proteins involved in mitochondrial fusion, including Opa1, whose levels are increased upon the over-expression of Myc. This results in a highly interconnected mitochondrial network in cells with high levels of Myc. This fused mitochondrial network is present despite the fact that Myc also increases the expression of proteins involved in mitochondrial fission as well. We sought to understand how Myc controls the expression of Opa1 and to determine if the high levels of mitochondrial fusion in Myc over-expressing cells are important in cellular transformation. We hypothesized that the increased mitochondrial fusion driven by the Myc-mediated increase in Opa1 may reduce apoptosis. Rat fibroblasts with inducible Myc expression were transfected with an OPA1-specific shRNA. These cells were characterized by a series of assays that measured different aspects of mitochondrial structure and function. After only 48h of Myc induction, mitochondrial mass increased by approximately two-fold compared to control cells; however, when Opa1 levels were reduced in this background (Myc+/Opa-), mitochondrial mass was decreased four-fold. The cells with decreased Opa1 expression but minimal Myc activity (Myc-/Opa-) had a punctate appearance to the mitochondria, which became even more dramatic in Myc+/Opa- cells. This was likely related to the ability of Myc to increase the proteins involved in fission. There was an approximate 50% decrease in the ability to perform oxidative phosphorylation (OXPHOS) when Myc-/Opa- cells were compared to Myc+/Opa- cells. This was consistent with the four-fold decrease in net ATP levels when Myc-/Opa- cells were compared to Myc+/Opa- cells. Finally, prolonged activation of Myc in cells with decreased expression of OPA1 leads to apoptosis. After 48 hours of Myc induction the Myc+/Opa- cells the cells gradually began to die and cultures were nearly devoid of viable cells within 10 days, whereas Myc-/Opa- cells remained almost completely viable. We believe that the unopposed mitochondrial fission in Myc+/Opa- cells results in an increase susceptibility to an early apoptotic death. The mechanisms involved in this phenomenon are being explored, as is the possibility of exploiting this consequence of Opa1 reduction as a means of selectively eliminating tumor cells that display Myc over-expression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1114. doi:1538-7445.AM2012-1114