title: Endothelin-1 (ET-1) induces resistance to bortezomib in human multiple myeloma cells via a pathway involving the ETB receptor and upregulation of proteasomal activity.
abstract: OBJECTIVE
  Bortezomib (BTZ) is used for the treatment of multiple myeloma (MM). However, a significant proportion of patients may be refractory to the drug. This study aimed to investigate whether the endothelin (ET-1) axis may act as an escape mechanism to treatment with bortezomib in MM cells.
  
  
  METHODS
  NCI-H929 and RPMI-8226 (human MM cell lines) were cultured with or without ET-1, BTZ, and inhibitors of the endothelin receptors. ET-1 levels were determined by ELISA, while the protein levels of its receptors and of the PI3K and MAPK pathways' components by western blot. Effects of ET-1 on cell proliferation were studied by MTT and on the ubiquitin proteasome pathway by assessing the chymotryptic activity of the 20S proteasome in cell lysates.
  
  
  RESULTS
  Endothelin receptors A and B (ETAR and ETBR, respectively) were found to be expressed in both cell lines, with the RPMI-8226 cells that are considered resistant to BTZ, expressing higher levels of ETBR and in addition secreting ET-1. Treatment of the NCI-H929 cells with ET-1 increased proliferation, while co-incubation of these cells with ET-1 and BTZ decreased BTZ efficacy with concomitant upregulation of 20S proteasomal activity. Si-RNA silencing or chemical blockade of ETBR abrogated the protective effects of ET-1. Finally, data suggest that the predominant signaling pathway involved in ET-1/ETBR-induced BTZ resistance in MM cells may be the MAPK pathway.
  
  
  CONCLUSIONS
  Our data suggest a possible role of the ET-1/ETBR axis in regulating the sensitivity of MM cells to BTZ. Thus, combining bortezomib with strategies to target the ET-1 axis could prove to be a novel promising therapeutic approach in MM.
authors.affiliation: Department of Medical Oncology, Faculty of Medicine, School of Health Sciences, University of Thessaly, Biopolis, 41110, Larissa, Greece.
authors.forename: Maria
authors.initials: M
authors.lastname: Vaiou
authors.affiliation: Laboratory of Biochemistry, Faculty of Medicine, School of Health Sciences, University of Thessaly, Biopolis, 41110, Larissa, Greece.
authors.forename: Evanthia
authors.initials: E
authors.lastname: Pangou
authors.affiliation: Laboratory of Biochemistry, Faculty of Medicine, School of Health Sciences, University of Thessaly, Biopolis, 41110, Larissa, Greece.
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Liakos
authors.affiliation: Department of Pharmacology, Faculty of Medicine, School of Health Sciences, University of Thessaly, Biopolis, 41110, Larissa, Greece.
authors.forename: Nikos
authors.initials: N
authors.lastname: Sakellaridis
authors.affiliation: Department of Hematology, Faculty of Medicine, School of Health Sciences, University of Thessaly, Biopolis, 41110, Larissa, Greece.
authors.forename: George
authors.initials: G
authors.lastname: Vassilopoulos
authors.affiliation: Department of Pharmacology, Faculty of Medicine, School of Health Sciences, University of Thessaly, Biopolis, 41110, Larissa, Greece. kdimas@med.uth.gr.
authors.forename: Konstantinos
authors.identifier: http://orcid.org/0000-0001-7481-9148
authors.initials: K
authors.lastname: Dimas
authors.affiliation: Department of Medical Oncology, Faculty of Medicine, School of Health Sciences, University of Thessaly, Biopolis, 41110, Larissa, Greece. cpapandreou@med.uth.gr.
authors.forename: Christos
authors.initials: C
authors.lastname: Papandreou
mesh_terms: D000069286:Bortezomib / Q000494:pharmacology*; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D065130:Endothelin A Receptor Antagonists / Q000494:pharmacology; D019332:Endothelin-1 / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D020935:MAP Kinase Signaling System; D009101:Multiple Myeloma / Q000188:drug therapy* / Q000201:enzymology / Q000378:metabolism*; D010456:Peptides, Cyclic / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D044022:Receptor, Endothelin A / Q000378:metabolism; D044023:Receptor, Endothelin B / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D065130:Endothelin A Receptor Antagonists; D019332:Endothelin-1; D010456:Peptides, Cyclic; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D025801:Ubiquitin; D000069286:Bortezomib; D019869:Phosphatidylinositol 3-Kinases; D046988:Proteasome Endopeptidase Complex; C072247:cyclo(Trp-Asp-Pro-Val-Leu)
keywords: Bortezomib; ETBR; Endothelin-1; Multiple myeloma; Ubiquitin–proteasome pathway