Autophagy is needed for the growth of pancreatic adenocarcinoma and has a cytoprotective effect against anticancer drugs
Introduction
Autophagy is a regulated process of degradation and recycling of cellular constituents, participating in organelle turnover and bioenergetic management of starvation [1]. During autophagy, an isolation membrane is initially formed (Fig. 1). The membrane wraps target cytoplasmic organelles/proteins and transforms into an autophagosome, which then fuses with a lysosome whereby its contents are degraded [2]. Microtubule-associated protein 1 light chain 3 (LC3) is a mammalian homologue of yeast autophagy-related gene (Atg) 8. LC3 exists in two molecular forms (Fig. 1). LC3-I is localised in the cytoplasm and is converted into the phosphatidylethanolamine-conjugated form LC3-II, which is associated with the autophagosome membrane [3], [4].
Autophagy has recently emerged as a significant mechanism in the development and treatment of malignancies including pancreatic cancer [5], [6], [7]. Controversy exists about the role of autophagy in pancreatic ductal adenocarcinoma [8], [9], [10], [11]. Yang et al. [11] reported that pancreatic cancer shows elevated autophagy, and inhibition of autophagy induces various cellular damages and suppresses cancer growth. Correspondingly, Fujii et al. [8] showed in their retrospective study that autophagy was activated in pancreatic cancer tissue, and correlated positively with poor patient outcome. The above studies indicate that autophagy has a cytoprotective effect, and it would be required for pancreatic cancer growth. By contrast Mukubou et al. [9] and Pardo et al. [10] indicated that autophagy is induced in pancreatic cancer cells by anticancer drugs, and that autophagy would contribute to cell death, and thus enhance cytotoxicity of anticancer drugs.
Therefore, the role of autophagy in pancreatic cancer remains unclear. The aim of this study was to investigate the role of autophagy in pancreatic cancer cells and in human pancreatic adenocarcinoma, and to provide insights into new strategies for treating pancreatic cancer.
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Reagents
Anticancer drugs 5-fluorouracil (5-FU) and gemcitabine (GEM) which are widely used in patients to treat pancreatic cancer [12] were chosen for the study (Fig. 1). Wortmannin (WM; PI3K inhibitor) inhibits the formation of autophagosomes (Fig. 1), and chloroquine (CQ; lysosomotropic agent) blocks lysosomal acidification and autophagosome degradation (Fig. 1) [11], [13], [14], [15], [16]. All drugs were purchased from Sigma–Aldrich (St. Louis, MO). The LC3 antibody was purchased from Cell
Effects of starvation and autophagy inhibitors on the expression of LC3-II in PANC-1
PANC-1 cells were incubated in normal medium (basal conditions), starved for 2 h in Hank’s solution (starvation) and starved for 2 h followed by normal medium for 2 h (recovery) (Fig. 2A). Western blotting showed that autophagy is active in these cells under basal conditions. The relative density of LC3-II increased by 69 ± 34% under starvation, and it returned back to the basal level after recovery (Fig. 2A).
The basal level of LC3-II in PANC-1 cells was decreased when the cells were incubated with
Discussion
The aim of this study was to investigate the role of autophagy in pancreatic cancer. Our results suggest that autophagy contributes to the growth of pancreatic cancer, and has a cytoprotective effect against anticancer drugs 5-FU and GEM in pancreatic cancer cells. Our findings support previous data about the importance of autophagy in pancreatic cancer biology. Further studies with cell lines representing more developed stages of pancreatic tumour differentiation will provide additional
Conflict of interest statement
None declared.
Acknowledgements
We are grateful to Prof. Hideo Baba, Department of Gastroenterological Surgery, Kumamoto University Graduate School of Medical Sciences, for general support. This work was financially supported by Sigrid Jusélius Foundation, Finland, The competitive research fund of Pirkanmaa Hospital District, Finland, and the Uehara Memorial Foundation, Japan.
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2021, Biochimica et Biophysica Acta - Reviews on CancerCitation Excerpt :In recent years, autophagy has been considered to prevent cancer occurrence but promote cancer progression, exhibiting contrasting effects [12]. Autophagy plays multiple roles that are thought to be connected to tumor growth, the epithelial-mesenchymal transition (EMT), metabolism, immunotherapy and chemoresistance mechanisms in pancreatic cancer [13–19]. Some clinical trials have suggested that combining chemotherapy and autophagy inhibitors might represent a promising treatment strategy [20].