title: Activation of ER stress and inhibition of EGFR N-glycosylation by tunicamycin enhances susceptibility of human non-small cell lung cancer cells to erlotinib.
abstract: OBJECTIVE
  The epidermal growth factor receptor (EGFR), an N-glycosylated transmembrane protein, is the target of erlotinib, an orally bioavailable agent approved for treatment of patients with non-small cell lung cancer (NSCLC). In this study, we examined whether inhibition of EGFR N-glycosylation and stimulation of endoplasmic reticulum (ER) stress by tunicamycin enhances erlotinib-induced growth inhibition in NSCLC cell lines.
  
  
  METHODS
  We examined the effects of tunicamycin and erlotinib on cytotoxicity of erlotinib-sensitive and resistant NSCLC cell lines, as well its effects on apoptotic pathways and on EGFR activation and subcellular localization.
  
  
  RESULTS
  A minimally cytotoxic concentration of tunicamycin (1 microM) resulted in approximatey 2.6-2.9 fold and approximatey 6.8-13.5 fold increase in erlotinib-induced antiproliferative effects in sensitive (H322 and H358) and resistant cell lines (A549 and H1650), respectively. We found that tunicamycin generated an aglycosylated form of 130 kDa EGFR. Tunicamycin additionally affected EGFR activation and subcellular localization. Interestingly, the combination of tunicamycin and erlotinib caused more inhibitory effect on EGFR phosphorylation than that of erlotinib alone. Moreover, the combination induced apoptosis in H1650 cells through induction of CHOP expression, activation of caspase-12 and caspase-3, cleavage of PARP and bak, and down-regulation of anti-apoptotic proteins bcl-xL and survivin.
  
  
  CONCLUSIONS
  Overall, our data demonstrate that tunicamycin significantly enhances the susceptibility of lung cancer cells to erlotinib, particularly sensitizing resistant cell lines to erlotinib, and that such sensitization may be associated with activation of the ER stress pathway and with inhibition of EGFR N-glycosylation.
authors.affiliation: Department of Oncology, Albert Einstein College of Medicine, Bronx, NY, USA.
authors.forename: Yi-He
authors.initials: YH
authors.lastname: Ling
authors.forename: Tianhong
authors.initials: T
authors.lastname: Li
authors.forename: Roman
authors.initials: R
authors.lastname: Perez-Soler
authors.forename: Missak
authors.initials: M
authors.lastname: Haigentz
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy* / Q000473:pathology; D053454:Caspase 12 / Q000187:drug effects / Q000378:metabolism; D053148:Caspase 3 / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D004721:Endoplasmic Reticulum / Q000378:metabolism; D066246:ErbB Receptors / Q000037:antagonists & inhibitors*; D000069347:Erlotinib Hydrochloride; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006031:Glycosylation / Q000187:drug effects; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000473:pathology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011799:Quinazolines / Q000494:pharmacology*; D051742:Transcription Factor CHOP / Q000187:drug effects / Q000378:metabolism; D014415:Tunicamycin / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: C497249:DDIT3 protein, human; D047428:Protein Kinase Inhibitors; D011799:Quinazolines; D014415:Tunicamycin; D051742:Transcription Factor CHOP; D000069347:Erlotinib Hydrochloride; D066246:ErbB Receptors; D053454:Caspase 12; D053148:Caspase 3