title: Glucose-regulated protein 78 (Grp78) confers chemoresistance to tumor endothelial cells under acidic stress.
abstract: OBJECTIVE
  This study was designed to investigate the activation of the unfolded protein response (UPR) in tumor associated endothelial cells (TECs) and its association with chemoresistance during acidic pH stress.
  
  
  METHODS
  Endothelial cells from human oral squamous cell carcinomas (OSCC) were excised by laser capture microdissection (LCM) followed by analysis of UPR markers (Grp78, ATF4 and CHOP) using quantitative PCR. Grp78 expression was also determined by immunostaining. Acidic stress was induced in primary human dermal microvascular endothelial cells (HDMECs) by treatment with conditioned medium (CM) from tumor cells grown under hypoxic conditions or by adjusting medium pH to 6.4 or 7.0 using lactic acid or hydrochloric acid (HCl). HDMEC resistance to the anti-angiogenic drug Sunitinib was assessed with SRB assay.
  
  
  RESULTS
  UPR markers, Grp78, ATF4 and CHOP were significantly upregulated in TECs from OSCC compared to HDMECs. HDMECs cultured in acidic CM (pH 6.0-6.4) showed increased expression of the UPR markers. However, severe acidosis led to marked cell death in HDMECs. Alternatively, HDMECs were able to adapt when exposed to chronic acidosis at pH 7.0 for 7 days, with concomittant increase in Grp78 expression. Chronic acidosis also confers drug resistance to HDMECs against Sunitinib. Knockdown of Grp78 using shRNA resensitizes HDMECs to drug treatment.
  
  
  CONCLUSIONS
  UPR induction in ECs under acidic pH conditions is related to chemoresistance and may contribute to therapeutic failures in response to chemotherapy. Targeting Grp78, the key component of the UPR pathway, may provide a promising approach to overcome ECs resistance in cancer therapy.
authors: Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, Ann Arbor, Michigan, United States of America; Department of Conservative Dentistry, Universidade Federal do Rio Grande do Sul School of Dentistry, Porto Alegre, Rio Grande do Sul, Brazil.
authors: Fernanda
authors: F
authors: Visioli
authors: Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, Ann Arbor, Michigan, United States of America.
authors: Yugang
authors: Y
authors: Wang
authors: Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, Ann Arbor, Michigan, United States of America.
authors: Goleeta N
authors: GN
authors: Alam
authors: Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, Ann Arbor, Michigan, United States of America.
authors: Yu
authors: Y
authors: Ning
authors: Department of Conservative Dentistry, Universidade Federal do Rio Grande do Sul School of Dentistry, Porto Alegre, Rio Grande do Sul, Brazil.
authors: Pantelis V
authors: PV
authors: Rados
authors: Department of Cariology, Restorative Sciences, and Endodontics, University of Michigan School of Dentistry, Ann Arbor, Michigan, United States of America.
authors: Jacques E
authors: JE
authors: Nör
authors: Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, Ann Arbor, Michigan, United States of America.
authors: Peter J
authors: PJ
authors: Polverini
mesh_terms: D000138:Acidosis / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology*; D020533:Angiogenesis Inhibitors / Q000494:pharmacology; D017209:Apoptosis; D015153:Blotting, Western; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D002453:Cell Cycle; D049109:Cell Proliferation; D002478:Cells, Cultured; D020405:Dermis / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D019008:Drug Resistance, Neoplasm; D000091342:Endoplasmic Reticulum Chaperone BiP; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D005455:Fluorescent Antibody Technique; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007124:Immunoenzyme Techniques; D061346:Laser Capture Microdissection; D009062:Mouth Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology*; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D056811:Unfolded Protein Response / Q000187:drug effects*
chemical_list: D020533:Angiogenesis Inhibitors; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D012333:RNA, Messenger