Abstract
Recent advances in experimental technologies and cancer models have made possible to demonstrate that the tumor is a dynamic system comprising heterogeneous populations of cancer cells organized in a hierarchical fashion with cancer stem cells (CSCs) at the apex. CSCs are immature cells characterized by self-renewal property and long-term repopulation potential. CSCs have been causally linked to cancer initiation, propagation, spreading, recurrence and relapse as well as to resistance to anticancer therapy. A growing body of evidence suggests that the function and physiology of CSCs may be influenced by genetic/epigenetic factors and tumor environment. In this context, macroautophagy is a lysosomal degradative process (herein referred to as autophagy) critical for the adaptive response to stress and the preservation of cellular and tissue homeostasis in all eukaryotes that may have a crucial role of in the origin, maintenance and invasiveness of CSCs. The activation of the autophagic machinery is also considered as an adaptive response of CSCs to perturbation of tumor microenvironment, caused for instance by anticancer therapy. Nevertheless, compelling preclinical and clinical evidence on the cytoprotective role of autophagy for CSCs is still missing. Here, we summarize the results on the contribution of autophagy in CSCs and how it impacts tumorigenesis and tumor progression. We also discuss the therapeutical potential of the modulation of autophagy as a means to eradicate CSCs.
Highlights
It is becoming increasingly evident that solid neoplasms are complex and dynamic entities composed of tumor cells and nontumor components, including infiltrating endothelial, stromal and immune cells, cancer-associated fibroblasts and constituents of extracellular matrix
Abbreviations used in this paper: AMPK, AMP-activated protein kinase; ATG, autophagy-related; BCL2, B-cell CLL/lymphoma 2; BECN1, Beclin 1; Chronic myeloid leukemia (CML), chronic myeloid leukemia; CQ, chloroquine; CSCs, cancer stem cells; DCIS, ductal carcinoma in situ; DCLK1, doublecortin-like kinase 1; ER, endoplasmic reticulum; LC3, microtubule-associated protein light chain 3; mTOR, mechanistic target of rapamycin; mTORC1, mTOR complex; PDAC, pancreatic ductal adenocarcinoma; PE, phosphatidylethanolamine; PI3K, phosphatidylinositol-3 kinase; PI3P, phosphatidylinositol-3-phosphate; RB1CC1, RB1-inducible coiled-coil 1; RCD, regulated cell death; shRNAs, short hairpin RNAs; TNBC, triple negative breast cancer; TSC1, tuberous sclerosis 1; ULK, unc-51 like autophagy activating kinase; VPS34, vacuolar protein sorting 34
Accumulating evidence suggests that the autophagic process actively contributes to the generation, maintenance, plasticity, distribution and migratory/invasion potential of CSCs (Fig. 2)
Summary
It is becoming increasingly evident that solid neoplasms are complex and dynamic entities composed of tumor cells and nontumor components, including infiltrating endothelial, stromal and immune cells, cancer-associated fibroblasts and constituents of extracellular matrix.
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