Inhibition of BRCA1 leads to increased chemoresistance to microtubule-interfering agents, an effect that involves the JNK pathway

Oncogene. 2001 Oct 4;20(45):6597-606. doi: 10.1038/sj.onc.1204812.


We have developed ribozymes (Rz) that inhibit BRCA1 expression in order to study the role of this gene in chemosensitivity. Two Rz, targeting positions 358 or 5282 of the BRCA1 mRNA, were cloned into the retroviral vector LXSN and lipofected into the breast cancer cell-line HBL100. We obtained 79-99% inhibition of BRCA1 expression, as determined by real-time quantitative PCR and by Western blotting. Decreased expression of BRCA1 led to sensitivity to the DNA damaging agents cisplatin and etoposide, resistance to the microtubule-interfering agents (MIA) taxol and vincristine. The molecular mechanism of resistance to MIA was investigated further by determining the status of the JNK pathway. We found that JNK1 expression was elevated, while JNK2 expression was decreased in Rz-expressing clones compared to controls. We have quantified the mRNA levels of BRCA1, JNK1, 2, MEK-4, -7 and c-jun after treatment with MIA. Vincristine treatment of control cells resulted in transcriptional repression of BRCA1, while the JNK1, 2, MEK-4, -7 and c-jun genes were induced. In Rz-treated cells, only JNK1 and MEK-4 were expressed and none was induced after MIA treatment. We then studied the phosphorylation of c-jun, a downstream effector of the JNK pathway. We observed a strong increase in phosphorylated c-jun after MIA treatment of the control cells but not in BRCA1-Rz treated cells, suggesting inhibition of the JNK pathway. These results show that the BRCA1-JNK pathway is involved in the cytotoxic response to MIA treatment, and inhibition of BRCA1 leads to transcriptional modifications of the JNK pathway.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents / pharmacology*
  • BRCA1 Protein / antagonists & inhibitors*
  • BRCA1 Protein / genetics
  • BRCA1 Protein / physiology
  • Breast Neoplasms / drug therapy
  • Breast Neoplasms / genetics
  • Breast Neoplasms / metabolism
  • Down-Regulation
  • Drug Resistance, Neoplasm
  • Humans
  • MAP Kinase Signaling System / drug effects*
  • Microtubules / drug effects*
  • Mitogen-Activated Protein Kinase 8
  • Mitogen-Activated Protein Kinase 9
  • Mitogen-Activated Protein Kinase Kinases / biosynthesis
  • Mitogen-Activated Protein Kinase Kinases / genetics
  • Mitogen-Activated Protein Kinases / genetics
  • Mitogen-Activated Protein Kinases / physiology
  • Paclitaxel / pharmacology
  • Proto-Oncogene Proteins c-jun / genetics
  • Proto-Oncogene Proteins c-jun / metabolism
  • RNA, Catalytic / pharmacology*
  • RNA, Messenger / drug effects
  • Spindle Apparatus / drug effects
  • Tumor Cells, Cultured
  • Vincristine / pharmacology


  • Antineoplastic Agents
  • BRCA1 Protein
  • Proto-Oncogene Proteins c-jun
  • RNA, Catalytic
  • RNA, Messenger
  • hammerhead ribozyme
  • Vincristine
  • Mitogen-Activated Protein Kinase 9
  • Mitogen-Activated Protein Kinase 8
  • Mitogen-Activated Protein Kinases
  • Mitogen-Activated Protein Kinase Kinases
  • Paclitaxel