BRCA1 is a central component of the DNA damage response mechanism and defects in BRCA1 confer sensitivity to a broad range of DNA damaging agents. BRCA1 is required for homologous recombination and DNA damage-induced S and G 2 /M phase arrest. We show here that BRCA1 is required for ATM-and ATR-dependent phosphorylation of p53, c-Jun, Nbs1 and Chk2 following exposure to ionizing or ultraviolet radiation, respectively, and is also required for ATM phosphorylation of CtIP. In contrast, DNA damageinduced phosphorylation of the histone variant H2AX is independent of BRCA1. We also show that the presence of BRCA1 is dispensable for DNA damageinduced phosphorylation of Rad9, Hus1 and Rad17, and for the relocalization of Rad9 and Hus1. We propose that BRCA1 facilitates the ability of ATM and ATR to phosphorylate downstream substrates that directly in¯uence cell cycle checkpoint arrest and apoptosis, but that BRCA1 is dispensable for the phosphorylation of DNA-associated ATM and ATR substrates.

There is now evidence to suggest that BRCA1 and BRCA2 are involved in the response of cells to DNA damage and cell cycle checkpoint control. This report examines the death pathways of human cells with various BRCA1 and BRCA2 genotypes after exposure to gamma-rays. A lack of functional BRCA1 and BRCA2 led to defective repair of DNA double-strand breaks in irradiated cells. This impairment resulted in a relaxation of cell cycle checkpoints, production of micronuclei, and a loss of proliferative capacity. Heterozygous BRCA1 and BRCA2 mutations also led to enhanced radiosensitivity, with an impaired proliferative capacity after irradiation. The existence of a phenotype related to radiosensitivity in BRCA1 +/7 and BRCA2 +/7 cells raises the question of the response of heterozygous women to radiation.

KiSS1 is a putative metastasis suppressor gene in melanoma and breast cancer-encoding kisspeptins, which are also described as neuroendocrine regulators of the gonadotropic axis. Negative as well as positive regulation of KiSS1 gene expression by estradiol (E 2 ) has been reported in the hypothalamus. Estrogen receptor a (ERa level is recognized as a marker of breast cancer, raising the question of whether expression of KiSS1 and its G-protein-coupled receptor (GPR54) is down-or upregulated by estrogens in breast cancer cells. KiSS1 was found to be expressed in MDA-MB-231, MCF7, and T47D cell lines, but not in ZR75-1, L56Br, and MDA-MB-435 cells. KiSS1 mRNA levels decreased significantly in ERa-negative MDA-MB-231 cells expressing recombinant ERa. In contrast, tamoxifen (TAM) treatment of ERa-positive MCF7 and T47D cells increased KiSS1 and GPR54 levels. The clinical relevance of this negative regulation of KiSS1 and GPR54 by E 2 was then studied in postmenopausal breast cancers. KiSS1 mRNA increased with the grade of the breast tumors. ERa-positive invasive primary tumors expressed sevenfold lower KiSS1 levels than ERanegative tumors. Among ERa-positive breast tumors from postmenopausal women treated with TAM, high KiSS1 combined with high GPR54 mRNA tumoral levels was unexpectedly associated with shorter relapse-free survival (RFS) relative to tumors expressing low tumoral mRNA levels of both genes. The contradictory observation of putative metastasis inhibitor role of kisspeptins and RFS to TAM treatment suggests that evaluation of KiSS1 and its receptor tumoral mRNA levels could be new interesting markers of the tumoral resistance to anti-estrogen treatment.