title: BRCC36 is essential for ionizing radiation-induced BRCA1 phosphorylation and nuclear foci formation.
abstract: We have previously reported the identification and characterization of a novel BRCA1/2 interacting protein complex, BRCC (BRCA1/2-containing complex). BRCC36, one of the proteins in BRCC, directly interacts with BRCA1, and regulates the ubiquitin E3 ligase activity of BRCC. Importantly, BRCC36 is aberrantly expressed in the vast majority of breast tumors, indicating a potential role in the pathogenesis of this disease. To further elucidate the functional consequence of abnormal BRCC36 expression in breast cancer, we have done in vivo silencing studies using small interfering RNAs targeting BRCC36 in breast cancer cell lines, i.e., MCF-7, ZR-75-1, and T47D. Knock-down of BRCC36 alone does not affect cell growth, but when combined with ionizing radiation (IR) exposure, it leads to an increase in the percentage of cells undergoing apoptosis when compared with the small interfering RNA control group in breast cancer cells. Immunoblot analysis shows that inhibition of BRCC36 has no effect on the activation of ATM, expression of p21 and p53, or BRCA1-BARD1 interaction following IR exposure. Importantly, BRCC36 depletion disrupts IR-induced phosphorylation of BRCA1. Immunofluorescent staining of BRCA1 and gamma-H2AX indicates that BRCC36 depletion prevents the formation of BRCA1 nuclear foci in response to DNA damage in breast cancer cells. These results show that down-regulation of BRCC36 expression impairs the DNA repair pathway activated in response to IR by inhibiting BRCA1 activation, thereby sensitizing breast cancer cells to IR-induced apoptosis.
authors.affiliation: Department of Medical Oncology, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
authors.forename: Xiaowei
authors.initials: X
authors.lastname: Chen
authors.forename: Cletus A
authors.initials: CA
authors.lastname: Arciero
authors.forename: Chunrong
authors.initials: C
authors.lastname: Wang
authors.forename: Dominique
authors.initials: D
authors.lastname: Broccoli
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Godwin
mesh_terms: D017209:Apoptosis / Q000502:physiology / Q000528:radiation effects; D019313:BRCA1 Protein / Q000037:antagonists & inhibitors / Q000378:metabolism*; D001943:Breast Neoplasms / Q000201:enzymology / Q000235:genetics / Q000378:metabolism* / Q000532:radiotherapy; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D004260:DNA Repair / Q000502:physiology; D015536:Down-Regulation; D015870:Gene Expression; D006801:Humans; D010766:Phosphorylation / Q000528:radiation effects; D034741:RNA, Small Interfering / Q000235:genetics; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*
chemical_list: D019313:BRCA1 Protein; D034741:RNA, Small Interfering; D025521:Tumor Suppressor Proteins; C102449:BARD1 protein, human; D044767:Ubiquitin-Protein Ligases