title: Autophagic homeostasis is required for the pluripotency of cancer stem cells.
abstract: Pluripotency is an important feature of cancer stem cells (CSCs) that contributes to self-renewal and chemoresistance. The maintenance of pluripotency of CSCs under various pathophysiological conditions requires a complex interaction between various cellular pathways including those involved in homeostasis and energy metabolism. However, the exact mechanisms that maintain the CSC pluripotency remain poorly understood. In this report, using both human and murine models of CSCs, we demonstrate that basal levels of autophagy are required to maintain the pluripotency of CSCs, and that this process is differentially regulated by the rate-limiting enzyme in the NAD+synthesis pathway NAMPT (nicotinamide phosphoribosyltransferase) and the transcription factor POU5F1/OCT4 (POU class 5 homeobox 1). First, our data show that the pharmacological inhibition and knockdown (KD) of NAMPT or the KDof POU5F1 in human CSCs significantly decreased the expression of pluripotency markers POU5F1, NANOG (Nanog homeobox) and SOX2 (SRY-box 2), and upregulated the differentiation markers TUBB3 (tubulin β 3 class III), CSN2 (casein β), SPP1 (secreted phosphoprotein 1), GATA6 (GATA binding protein 6), T (T brachyury transcription factor) and CDX2 (caudal type homeobox 2). Interestingly, these pluripotency-regulating effects of NAMPT and POU5F1 were accompanied by contrasting levels of autophagy, wherein NAMPT KDpromoted while POU5F1 KDinhibited the autophagy machinery. Most importantly, any deviation from the basal level of autophagy, either increase (via rapamycin, serum starvation or Tat-beclin 1 [Tat-BECN1] peptide) or decrease (via ATG7 or ATG12 KD), strongly decreased the pluripotency and promoted the differentiation and/or senescence of CSCs. Collectively, these results uncover the link between the NAD+biosynthesis pathway, CSC transcription factor POU5F1 and pluripotency, and further identify autophagy as a novel regulator of pluripotency of CSCs.
authors.affiliation: a Department of Microbiology and Immunology , Dalhousie University , Halifax , Nova Scotia , Canada.
authors.forename: Tanveer
authors.initials: T
authors.lastname: Sharif
authors.affiliation: a Department of Microbiology and Immunology , Dalhousie University , Halifax , Nova Scotia , Canada.
authors.forename: Emma
authors.initials: E
authors.lastname: Martell
authors.affiliation: a Department of Microbiology and Immunology , Dalhousie University , Halifax , Nova Scotia , Canada.
authors.forename: Cathleen
authors.initials: C
authors.lastname: Dai
authors.affiliation: a Department of Microbiology and Immunology , Dalhousie University , Halifax , Nova Scotia , Canada.
authors.forename: Barry E
authors.initials: BE
authors.lastname: Kennedy
authors.affiliation: a Department of Microbiology and Immunology , Dalhousie University , Halifax , Nova Scotia , Canada.
authors.forename: Patrick
authors.initials: P
authors.lastname: Murphy
authors.affiliation: b Department of Pathology , Dalhousie University , Halifax , Nova Scotia , Canada.
authors.forename: Derek R
authors.initials: DR
authors.lastname: Clements
authors.affiliation: b Department of Pathology , Dalhousie University , Halifax , Nova Scotia , Canada.
authors.forename: Youra
authors.initials: Y
authors.lastname: Kim
authors.affiliation: a Department of Microbiology and Immunology , Dalhousie University , Halifax , Nova Scotia , Canada.|b Department of Pathology , Dalhousie University , Halifax , Nova Scotia , Canada.
authors.forename: Patrick W K
authors.initials: PW
authors.lastname: Lee
authors.affiliation: a Department of Microbiology and Immunology , Dalhousie University , Halifax , Nova Scotia , Canada.|b Department of Pathology , Dalhousie University , Halifax , Nova Scotia , Canada.|c Centre for Innovative and Collaborative Health Services Research, Quality and System Performance, IWK Health Centre , Halifax , Nova Scotia , Canada.
authors.forename: Shashi A
authors.initials: SA
authors.lastname: Gujar
mesh_terms: D000818:Animals; D001343:Autophagy / Q000187:drug effects; D000071186:Beclin-1 / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D016922:Cellular Senescence / Q000187:drug effects; D016207:Cytokines / Q000037:antagonists & inhibitors / Q000378:metabolism; D004317:Doxorubicin / Q000494:pharmacology; D006706:Homeostasis / Q000187:drug effects; D051379:Mice; D008954:Models, Biological; D014411:Neoplastic Stem Cells / Q000187:drug effects / Q000201:enzymology / Q000473:pathology*; D054409:Nicotinamide Phosphoribosyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism; D050814:Octamer Transcription Factor-3 / Q000378:metabolism; D051059:PTEN Phosphohydrolase / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D039904:Pluripotent Stem Cells / Q000187:drug effects / Q000473:pathology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism
chemical_list: D000071186:Beclin-1; D016207:Cytokines; D050814:Octamer Transcription Factor-3; C494173:POU5F1 protein, human; D004317:Doxorubicin; D054409:Nicotinamide Phosphoribosyltransferase; C085455:nicotinamide phosphoribosyltransferase, human; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D051059:PTEN Phosphohydrolase; D020123:Sirolimus
keywords: POU5F1/Oct4; autophagy; cancer stem cells; differentiation; pluripotency; senescence