title: Inhibition of Phosphatidylcholine-Specific Phospholipase C Interferes with Proliferation and Survival of Tumor Initiating Cells in Squamous Cell Carcinoma.
abstract: OBJECTIVE
  The role of phosphatidylcholine-specific phospholipase C (PC-PLC), the enzyme involved in cell differentiation and proliferation, has not yet been explored in tumor initiating cells (TICs). We investigated PC-PLC expression and effects of PC-PLC inhibition in two adherent (AD) squamous carcinoma cell lines (A431 and CaSki), with different proliferative and stemness potential, and in TIC-enriched floating spheres (SPH) originated from them.
  
  
  RESULTS
  Compared with immortalized non-tumoral keratinocytes (HaCaT) A431-AD cells showed 2.5-fold higher PC-PLC activity, nuclear localization of a 66-kDa PC-PLC isoform, but a similar distribution of the enzyme on plasma membrane and in cytoplasmic compartments. Compared with A431-AD, A431-SPH cells showed about 2.8-fold lower PC-PLC protein and activity levels, but similar nuclear content. Exposure of adherent cells to the PC-PLC inhibitor D609 (48h) induced a 50% reduction of cell proliferation at doses comprised between 33 and 50 μg/ml, without inducing any relevant cytotoxic effect (cell viability 95±5%). In A431-SPH and CaSki-SPH D609 induced both cytostatic and cytotoxic effects at about 20 to 30-fold lower doses (IC50 ranging between 1.2 and 1.6 μg/ml). Furthermore, D609 treatment of A431-AD and CaSki-AD cells affected the sphere-forming efficiency, which dropped in both cells, and induced down-modulation of stem-related markers mRNA levels (Oct4, Nestin, Nanog and ALDH1 in A431; Nestin and ALDH1 in CaSki cells).
  
  
  CONCLUSIONS
  These data suggest that the inhibition of PC-PLC activity may represent a new therapeutic approach to selectively target the most aggressive and tumor promoting sub-population of floating spheres originated from squamous cancer cells possessing different proliferative and stemness potential.
authors.affiliation: Department of Cell Biology and Neurosciences, Istituto Superiore di Sanità, Rome, Italy.
authors.forename: Serena
authors.initials: S
authors.lastname: Cecchetti
authors.affiliation: Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: Ileana
authors.initials: I
authors.lastname: Bortolomai
authors.affiliation: Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: Renata
authors.initials: R
authors.lastname: Ferri
authors.affiliation: Department of Cell Biology and Neurosciences, Istituto Superiore di Sanità, Rome, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Mercurio
authors.affiliation: Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: Silvana
authors.initials: S
authors.lastname: Canevari
authors.affiliation: Department of Cell Biology and Neurosciences, Istituto Superiore di Sanità, Rome, Italy.
authors.forename: Franca
authors.initials: F
authors.lastname: Podo
authors.affiliation: Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Miotti
authors.affiliation: Department of Cell Biology and Neurosciences, Istituto Superiore di Sanità, Rome, Italy.
authors.forename: Egidio
authors.initials: E
authors.lastname: Iorio
mesh_terms: D001952:Bridged-Ring Compounds / Q000494:pharmacology; D002294:Carcinoma, Squamous Cell / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D000066673:Cell Self Renewal; D002470:Cell Survival / Q000187:drug effects; D066246:ErbB Receptors / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D015603:Keratinocytes / Q000187:drug effects / Q000378:metabolism; D014411:Neoplastic Stem Cells / Q000187:drug effects* / Q000378:metabolism*; D009636:Norbornanes; D010766:Phosphorylation; D021381:Protein Transport; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D013859:Thiocarbamates; D013871:Thiones / Q000494:pharmacology; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors* / Q000378:metabolism*
chemical_list: D001952:Bridged-Ring Compounds; D009636:Norbornanes; D013859:Thiocarbamates; D013871:Thiones; C046498:tricyclodecane-9-yl-xanthogenate; D066246:ErbB Receptors; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D010738:Type C Phospholipases; C105598:phosphatidylcholine-specific phospholipase C