title: Transient TNF regulates the self-renewing capacity of stem-like label-retaining cells in sphere and skin equivalent models of melanoma.
abstract: BACKGROUND
  It is well established that inflammation promotes cancer, including melanoma, although the exact mechanisms involved are less known. In this study, we tested the hypothesis that inflammatory factors affect the cancer stem cell (CSC) compartment responsible for tumor development and relapse.
  
  
  RESULTS
  Using an inducible histone 2B-GFP fusion protein as a tracer of cell divisional history, we determined that tumor necrosis factor (TNF), which is a classical pro-inflammatory cytokine, enlarged the CSC pool of GFP-positive label-retaining cells (LRCs) in tumor-like melanospheres. Although these cells acquired melanoma stem cell markers, including ABCB5 and CD271, and self-renewal ability, they lost their capacity to differentiate, as evidenced by the diminished MelanA expression in melanosphere cells and the loss of pigmentation in a skin equivalent model of human melanoma. The undifferentiated cell phenotype could be reversed by LY294002, which is an inhibitor of the PI3K/AKT signaling pathway, and this reversal was accompanied by a significant reduction in CSC phenotypic markers and functional properties. Importantly, the changes induced by a transient exposure to TNF were long-lasting and observed for many generations after TNF withdrawal.
  
  
  CONCLUSIONS
  We conclude that pro-inflammatory TNF targets the quiescent/slow-cycling melanoma SC compartment and promotes PI3K/AKT-driven expansion of melanoma SCs most likely by preventing their asymmetrical self-renewal. This TNF effect is maintained and transferred to descendants of LRC CSCs and is manifested in the absence of TNF, suggesting that a transient exposure to inflammatory factors imprints long-lasting molecular and/or cellular changes with functional consequences long after inflammatory signal suppression. Clinically, these results may translate into an inflammation-triggered accumulation of quiescent/slow-cycling CSCs and a post-inflammatory onset of an aggressive tumor.
authors.forename: Pauline
authors.initials: P
authors.lastname: Ostyn
authors.forename: Raja
authors.initials: R
authors.lastname: El Machhour
authors.forename: Severine
authors.initials: S
authors.lastname: Begard
authors.forename: Nuria
authors.initials: N
authors.lastname: Kotecki
authors.forename: Jerome
authors.initials: J
authors.lastname: Vandomme
authors.forename: Pilar
authors.initials: P
authors.lastname: Flamenco
authors.forename: Pascaline
authors.initials: P
authors.lastname: Segard
authors.forename: Bernadette
authors.initials: B
authors.lastname: Masselot
authors.forename: Pierre
authors.initials: P
authors.lastname: Formstecher
authors.forename: Yasmine
authors.initials: Y
authors.lastname: Touil
authors.forename: Renata
authors.initials: R
authors.lastname: Polakowska
mesh_terms: D000328:Adult; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D005260:Female; D005347:Fibroblasts; D006801:Humans; D015603:Keratinocytes; D008545:Melanoma / Q000378:metabolism*; D014411:Neoplastic Stem Cells / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D012867:Skin / Q000378:metabolism; D012878:Skin Neoplasms / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
chemical_list: D014409:Tumor Necrosis Factor-alpha; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt