title: BRCA1 downregulation leads to premature inactivation of spindle checkpoint and confers paclitaxel resistance.
abstract: BRCA1 germline mutations predispose women to early onset, familial breast and ovarian cancer. BRCA1 has been recently implicated in the cellular response to agents that disrupt the mitotic spindle. In this report, we studied BRCA1 contribution to paclitaxel response in MCF-7 breast cancer cells. We show that MCF-7 cells transfected with BRCA1 siRNA display a significant increase in resistance to paclitaxel compared with the control cells. We next demonstrate that downregulation of BRCA1 reduces the mitotic index and triggers premature cyclin B1 degradation and decrease in Cdk1 activity following paclitaxel treatment, suggesting that BRCA1 downregulation results in precocious inactivation of the spindle checkpoint. These findings were confirmed by showing that BRCA1 downregulation induces premature sister-chromatids separation in MCF-7 cells following spindle damage. Furthermore, we show that BRCA1 up-regulates the expression of the protein kinase BubR1, essential component of the functional spindle checkpoint, whose downregulation is known to result in paclitaxel resistance in MCF-7 cells. Altogether, our findings support the notion that downregulation of BRCA1 expression mediates paclitaxel resistance through premature inactivation of spindle checkpoint in MCF-7 breast cancer cells. They link BRCA1 to the mitotic checkpoint that plays an essential role in the maintenance of chromosomal stability.
authors.affiliation: LBCMCP, UMR 5088 CNRS, Université Paul Sabatier III, Toulouse, France.
authors.forename: C
authors.initials: C
authors.lastname: Chabalier
authors.forename: C
authors.initials: C
authors.lastname: Lamare
authors.forename: C
authors.initials: C
authors.lastname: Racca
authors.forename: M
authors.initials: M
authors.lastname: Privat
authors.forename: A
authors.initials: A
authors.lastname: Valette
authors.forename: F
authors.initials: F
authors.lastname: Larminat
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D019313:BRCA1 Protein / Q000235:genetics* / Q000378:metabolism; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002453:Cell Cycle / Q000502:physiology; D045744:Cell Line, Tumor; D043171:Chromosomal Instability; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D005260:Female; D006801:Humans; D017239:Paclitaxel / Q000494:pharmacology*; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D034741:RNA, Small Interfering / Q000378:metabolism; D008941:Spindle Apparatus / Q000187:drug effects* / Q000648:ultrastructure; D015854:Up-Regulation
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D019313:BRCA1 Protein; D034741:RNA, Small Interfering; D011494:Protein Kinases; C584277:BUB1 protein, human; C090464:Bub1 spindle checkpoint protein; D017346:Protein Serine-Threonine Kinases; D017239:Paclitaxel