The microtubule-associated protein light chain 3 MAP1LC3 (LC3) and GABARAPL1 and 2 are the major proteins to monitor autophagy. Here, we analyzed the role of both MAP1LC3, GABARAPL1 and 2 in breast cancer cells and primary human breast cancer. HER2 amplified (BT474, SKBR3, MDA-MB-453), ER positive (MCF7, T47D) and triple negative (MDAMB231) breast cancer cell lines were studied in response to hypoxia, in high [25mM] and low glucose [5mM] treatment. Low glucose increased the basal levels for LC3A-II, LC3B-II and GABARAPL2-II in BT474, MCF7 and MDAMB231 cell lines. SKBR3 cell line had the lowest autophagic protein levels for LC3B-II, and Gabarapl2-II and was the most resistance to the autophagy inhibition mediated using siRNAs to all theseIn hypoxia both LC3B (up to 8 fold) and GABARAPL1 (up to 12 fold) mRNA expression were induced in all cell lines (p<0.001). MAP1LC3A knockdown significantly decrease cell proliferation in BT474, MCF7 and MDAMB231 while GABARAPL2 knockdown additionally decreased baseline cell proliferation in T47D and SKBR3 breast cancer cells (p<0.05, n = 3). Moreover, using the Seahorse, decreased MAP1LC3A and GABARAPL2 expression by siRNA led to cellular bioenergetic changes including increased basal oxygen consumption of the MCF7.
Co-expression analysis of autophagic genes define distinctive clusters of MAP1LC3, GABARAPL 1 and 2 with the hypoxic signature in breast cancer subtypes using the METABRIC series.
The expression levels of the MAP1LC3 and GABARAPL1 and 2 among the breast cancer subtypes and normal tissue showed significant suppession of all of them in cancer compared to normal breast tissue. In conclusion, all the pathways were suppressed at RNA level in cancer compared to normal, baseline levels were not associated with core classification of breast cancer types. These latter data were confirmed in a breast cancer cell line panel, which showed a marked variation in inducibility by environemntal stress and role in survival under low glucose and hypoxia. Thus analysis of induced gene expression in response to stress may be important, or heterogeneity in selection of tumors for anti-autophagy therapy.
Citation Format: Christos E. Zois, Syed Haider, Simon Wigfield, Alexandra Giatromanolaki, Efthimios Sivridis, Karl Morten, Ioannis Roxanis, Russell Leek, Francesca Buffa, Michael Koukourakis, Adrian L. Harris. Differential regulation of LC3 A and B, GABARAPL 1 and 2 autophagy genes by micro-environmental stress and role in breast cancer survival. [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 2903. doi:10.1158/1538-7445.AM2015-2903