title: Involvement of Cox-2 in the metastatic potential of chemotherapy-resistant breast cancer cells.
abstract: BACKGROUND
  A major problem with the use of current chemotherapy regimens for several cancers, including breast cancer, is development of intrinsic or acquired drug resistance, which results in disease recurrence and metastasis. However, the mechanisms underlying this drug resistance are unknown. To study the molecular mechanisms underlying the invasive and metastatic activities of drug-resistant cancer cells, we generated a doxorubicin-resistant MCF-7 breast cancer cell line (MCF-7/DOX).
  
  
  METHODS
  We used MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays, flow cytometry assays, DNA fragmentation assays, Western blot analysis, cell invasion assays, small interfering RNA (siRNA) transfection, reverse transcription-polymerase chain reaction, experimental lung metastasis models, and gelatin and fibrinogen/plasminogen zymography to study the molecular mechanism of metastatic activities in MCF-7/DOX cells.
  
  
  RESULTS
  We found that MCF-7/DOX acquired invasive activities. In addition, Western blot analysis showed increased expression of epidermal growth factor receptor (EGFR) and Cox-2 in MCF-7/DOX cells. Inhibition of Cox-2, phosphoinositide 3-kinase (PI3K)/Akt, or mitogen-activated protein kinase (MAPK) pathways effectively inhibited the invasive activities of MCF-7/DOX cells. Gelatin and fibrinogen/plasminogen zymography analysis showed that the enzymatic activities of matrix metalloproteinase-2 (MMP-2), MMP-9, and urokinase-type plasminogen activator were markedly higher in MCF-7/DOX cells than in the MCF-7 cells. In vitro invasion assays and mouse models of lung metastasis demonstrated that MCF-7/DOX cells acquired invasive abilities. Using siRNAs and agonists specific for prostaglandin E (EP) receptors, we found that EP1 and EP3 played important roles in the invasiveness of MCF-7/DOX cells.
  
  
  CONCLUSIONS
  We found that the invasive activity of MCF-7/DOX cells is mediated by Cox-2, which is induced by the EGFR-activated PI3K/Akt and MAPK pathways. In addition, EP1 and EP3 are important in the Cox-2-induced invasion of MCF-7/DOX cells. Therefore, not only Cox-2 but also EP1 and EP3 could be important targets for chemosensitization and inhibition of metastasis in breast cancers that are resistant to chemotherapy.
authors.affiliation: Division of Cancer Biology, National Cancer Center, Ilsan-ro 323, Ilsandong-gu, Goyang-si, Gyeonggi-do 410-769, Republic of Korea.
authors.forename: Ju-Hee
authors.initials: JH
authors.lastname: Kang
authors.forename: Ki-Hoon
authors.initials: KH
authors.lastname: Song
authors.forename: Kyung-Chae
authors.initials: KC
authors.lastname: Jeong
authors.forename: Sunshin
authors.initials: S
authors.lastname: Kim
authors.forename: Changsun
authors.initials: C
authors.lastname: Choi
authors.forename: Chang Hoon
authors.initials: CH
authors.lastname: Lee
authors.forename: Seung Hyun
authors.initials: SH
authors.lastname: Oh
mesh_terms: D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D051546:Cyclooxygenase 2 / Q000235:genetics / Q000378:metabolism*; D004317:Doxorubicin / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm; D066246:ErbB Receptors / Q000378:metabolism; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism / Q000556:secondary; D008325:Mammary Neoplasms, Experimental / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009361:Neoplasm Invasiveness; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D034622:RNA Interference; D058306:Receptors, Prostaglandin E, EP1 Subtype / Q000235:genetics / Q000378:metabolism; D058308:Receptors, Prostaglandin E, EP3 Subtype / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D014183:Transplantation, Heterologous
chemical_list: D000903:Antibiotics, Antineoplastic; C545635:PTGER1 protein, human; C545647:PTGER3 protein, human; D058306:Receptors, Prostaglandin E, EP1 Subtype; D058308:Receptors, Prostaglandin E, EP3 Subtype; D004317:Doxorubicin; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D019869:Phosphatidylinositol 3-Kinases; D066246:ErbB Receptors; D020928:Mitogen-Activated Protein Kinases