The differential expression of miRNAs in breast cancer cell-lines upon autophagy induction

• Main Author: Armstrong, Luke Jeffery
• Language: English
• Published: University of British Columbia 2010
• Online Access: http://hdl.handle.net/2429/25590

Autophagy is a catabolic process of self-digestion that occurs at basal levels in all cells, degrading old and damaged components such as proteins and organelles. Autophagy is upregulated in response to cellular stress, including the types imposed on cancer cells, and its role in these circumstances is often to facilitate cell survival. However, the molecular mechanisms regulating autophagy in response to cellular stress are still not well understood. Other components of the cell that are regulated in response to cellular stress are small non-coding portions of RNA termed microRNAs (miRNAs) that act to control protein levels in the cell by degrading mRNA targets or repressing their translation. The overall objective of this research was to identify candidate miRNA regulators of autophagy. My hypothesis was that miRNAs that regulate autophagy will demonstrate differential expression in response to cell stresses that induce autophagy. To test this hypothesis, I conducted miRNA expression profiling by Illumina sequencing in untreated BT-474 breast cancer cells and in BT-474 cells treated with a high dose of tamoxifen, a known inducer of autophagy. 113 distinct miRNAs were found to be significantly differentially expressed (p<0.05 and >1.5 fold) between the tamoxifen treated sample and control, and the differential expression of a subset of these miRNAs was validated using QRT-PCR. Using the online miRNA resource, TargetScan, 27 of the differentially expressed miRNAs were found to have potential autophagy-related targets, and of these, seven were selected to undergo further expression analysis in two additional breast cancer cell-lines using an additional autophagy inducing treatment, nutrient deprivation. Four of the selected miRNAs demonstrated similar patterns of differential expression in all three breast cancer cell-lines under the two different autophagy-inducing conditions. These four miRNAs consistently showed decreased expression when autophagy was induced, and have the potential to be direct regulators of the autophagy pathway upon cell stress induction in breast cancer cells. Understanding the mechanisms underlying the regulation of stress-induced autophagy may provide insight into the role autophagy plays in breast cancer and reveal potential targets to alter the process for clinical benefit.