title: Analysis of marker-defined HNSCC subpopulations reveals a dynamic regulation of tumor initiating properties.
abstract: Head and neck squamous carcinoma (HNSCC) tumors carry dismal long-term prognosis and the role of tumor initiating cells (TICs) in this cancer is unclear. We investigated in HNSCC xenografts whether specific tumor subpopulations contributed to tumor growth. We used a CFSE-based label retentions assay, CD49f (α6-integrin) surface levels and aldehyde dehydrogenase (ALDH) activity to profile HNSCC subpopulations. The tumorigenic potential of marker-positive and -negative subpopulations was tested in nude (Balb/c nu/nu) and NSG (NOD.Cg-Prkdc(scid) Il2rg(tm1Wjl)/SzJ) mice and chicken embryo chorioallantoic membrane (CAM) assays. Here we identified in HEp3, SQ20b and FaDu HNSCC xenografts a subpopulation of G0/G1-arrested slow-cycling CD49f(high)/ALDH1A1(high)/H3K4/K27me3(low) subpopulation (CD49f+) of tumor cells. A strikingly similar CD49f(high)/H3K27me3(low) subpopulation is also present in primary human HNSCC tumors and metastases. While only sorted CD49f(high)/ALDH(high), label retaining cells (LRC) proliferated immediately in vivo, with time the CD49f(low)/ALDH(low), non-LRC (NLRC) tumor cell subpopulations were also able to regain tumorigenic capacity; this was linked to restoration of CD49f(high)/ALDH(high), label retaining cells. In addition, CD49f is required for HEp3 cell tumorigenicity and to maintain low levels of H3K4/K27me3. CD49f+ cells also displayed reduced expression of the histone-lysine N-methyltransferase EZH2 and ERK1/2 phosphorylation. This suggests that although transiently quiescent, their unique chromatin structure is poised for rapid transcriptional activation. CD49f- cells can "reprogram" and also achieve this state eventually. We propose that in HNSCC tumors, epigenetic mechanisms likely driven by CD49f signaling dynamically regulate HNSCC xenograft phenotypic heterogeneity. This allows multiple tumor cell subpopulations to drive tumor growth suggesting that their dynamic nature renders them a "moving target" and their eradication might require more persistent strategies.
authors.affiliation: Division of Hematology and Oncology, Department of Medicine, Mount Sinai School of Medicine, New York, New York, United States of America.
authors.forename: Paloma
authors.initials: P
authors.lastname: Bragado
authors.forename: Yeriel
authors.initials: Y
authors.lastname: Estrada
authors.forename: Maria Soledad
authors.initials: MS
authors.lastname: Sosa
authors.forename: Alvaro
authors.initials: A
authors.lastname: Avivar-Valderas
authors.forename: David
authors.initials: D
authors.lastname: Cannan
authors.forename: Eric
authors.initials: E
authors.lastname: Genden
authors.forename: Marita
authors.initials: M
authors.lastname: Teng
authors.forename: Aparna C
authors.initials: AC
authors.lastname: Ranganathan
authors.forename: Huei-Chi
authors.initials: HC
authors.lastname: Wen
authors.forename: Avnish
authors.initials: A
authors.lastname: Kapoor
authors.forename: Emily
authors.initials: E
authors.lastname: Bernstein
authors.forename: Julio A
authors.initials: JA
authors.lastname: Aguirre-Ghiso
mesh_terms: D000818:Animals; D002294:Carcinoma, Squamous Cell / Q000378:metabolism / Q000473:pathology*; D045744:Cell Line, Tumor; D002642:Chick Embryo; D006258:Head and Neck Neoplasms / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D051379:Mice; D016688:Mice, Inbred NOD; D008819:Mice, Nude; D014411:Neoplastic Stem Cells / Q000378:metabolism / Q000473:pathology*; D000077195:Squamous Cell Carcinoma of Head and Neck