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UBC Theses and Dissertations

Investigating the role of the inhibitor of apoptosis protein, Apollon, in the regulation of autophagy in breast cancer cells Hannigan, Adrienne Michelle

Abstract

Macroautophagy (autophagy) is a lysosomal process for degrading cytoplasmic proteins and organelles for maintenance of homeostasis as well as for bioenergetic and biosynthetic needs. During nutrient deprivation and chemotherapy, both tumour-related stresses, autophagy is upregulated. The molecules and pathways involved in the regulation of autophagy in response to these stresses are still not well understood. Several recent studies have uncovered links between components of autophagy and apoptosis. As there is increasing evidence indicating that many anti-cancer therapeutics affect both autophagy and apoptosis, it is critical to identify the relationships between these pathways to develop more rational therapies. A previous study identified several Drosophila melanogaster genes with autophagy-regulating functions. One of these genes was dBruce, a member of the inhibitor of apoptosis (IAP) gene family, which was found to negatively regulate autophagy in Drosophila cells in vitro and in vivo. The mammalian homologue of dBruce, Apollon, is overexpressed in several cancers, and Apollon knockdown has been shown to sensitize some cancer cells to chemotherapy. These findings led to the suggestion that Apollon may be a promising target for cancer therapy. As autophagy has been shown to play a role in cancer development and treatment, a link between Apollon and autophagy may have clinical implications. My hypothesis in this study was that Apollon, the human homologue of dBruce, is a negative regulator of autophagy in human breast cancer cells. I tested this hypothesis using three different breast cancer cell lines, SKBR3, BT474 and MCF-7, to determine whether Apollon knockdown had an effect on autophagy under fed or starved conditions. After Apollon knockdown, MCF-7 and SKBR3 cells showed a significant increase in GFP-LC3 and/or MDC puncta under both fed and starved conditions. Further analysis in MCF-7 cells confirmed that Apollon knockdown led to an induction of the complete autophagy process as determined by two autophagy flux assays. These results show that reducing Apollon expression induces autophagy and thus Apollon is a negative regulator of autophagy in human breast cancer cell lines. Further studies will be required to determine whether Apollon knockdown-induced autophagy would be beneficial for cancer therapy.

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