title: Phosphoprotein analysis reveals MEK inhibition as a way to target non-small cell lung cancer tumor initiating cells.
abstract: OBJECTIVE
  We aimed to analyze the activation status of commonly deregulated receptor tyrosine kinases (RTK) in human non-small cell lung cancer (NSCLC) tumor initiating cells (TIC) previously demonstrated to be refractory to ionizing radiation and chemotherapy.
  
  
  METHODS
  Phosphorylated RTK and important signaling nodes were assayed using PathScan RTK Signaling Antibody Array Kit in NSCLC TIC and bulk cells 4 h post-irradiation (IR) and validated by Western blot. The effect of mitogen- activated protein kinase kinase (MEK) inhibition combined with IR was analyzed using clonogenic assay.
  
  
  RESULTS
  H125 TIC displayed decreased basal phosphorylation of insulin-like growth factor 1 receptor (IGF-1R) and signal transducer and activator of transcription 1 (STAT1) (Tyr701) as compared to bulk cells. Total IGF-1R levels were significantly lower in NSCLC TIC as compared to bulk cells. A higher degree of extracellular signal-regulated kinase (ERK) phosphorylation was evident in TIC and concordantly MEK inhibition reduced TIC viability. Moreover, MEK inhibition also decreased clonogenicity upon IR suggesting that MEK and downstream signaling impart on TIC radiation response.
  
  
  CONCLUSIONS
  We demonstrate reduced basal phosphorylation of several signaling pathways including lower total IGF-1R levels in NSCLC TIC which is of potential concern for RTK inhibitor use. Importantly, MEK inhibition decreased cell viability of NSCLC TIC alone or in combination with IR.
authors.affiliation: Karolinska Biomics Center, Department of Oncology-Pathology, Karolinska Institutet and Karolinska University Hospital , Stockholm , Sweden.
authors.forename: Lovisa
authors.initials: L
authors.lastname: Lundholm
authors.forename: Petra
authors.initials: P
authors.lastname: Hååg
authors.forename: Therese
authors.initials: T
authors.lastname: Juntti
authors.forename: Rolf
authors.initials: R
authors.lastname: Lewensohn
authors.forename: Kristina
authors.initials: K
authors.lastname: Viktorsson
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000473:pathology*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D004249:DNA Damage; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology*; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000528:radiation effects; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D058990:Molecular Targeted Therapy; D014411:Neoplastic Stem Cells / Q000187:drug effects / Q000473:pathology* / Q000528:radiation effects; D010641:Phenotype; D010750:Phosphoproteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects / Q000528:radiation effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000378:metabolism; D050794:STAT1 Transcription Factor / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D010750:Phosphoproteins; D047428:Protein Kinase Inhibitors; D050794:STAT1 Transcription Factor; D017526:Receptor, IGF Type 1; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases
keywords: ERK; IGF-1R; MEK; Tumor initiating cell; cancer stem cell; non-small cell lung cancer