IntroductionThe incidence of breast cancer has been increasing steadily over the past 60 years [1], today affecting one in eight women in the United States [2]. Despite tremendous efforts to understand the disease, less than 50% of all cases are of known etiology such as genetic inheritance, first-degree relatives with breast cancer, and age of menstruation and menopause [3].A large group of lipophilic organochlorines are found to persist in the environment and to biomagnify through the food chain. This group includes pesticides, polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-dioxins/ polychlorinated dibenzo-furans [4][5][6][7][8]. Many of these compounds can interfere with a wide range of hormonal responses [9][10][11][12][13], including estrogen receptor (ER)-mediated responses. Due to their lipophilic nature, bp = base pair; DMEM = Dulbecco's modified Eagle's medium; E2 = 17β-estradiol; ER = estrogen receptor; PCB = polychlorinated biphenyl; PCR = polymerase chain reaction; POC = persistent organochlorine; TCDD = 2,3,7,8 tetrachlorodibenzo-p-dioxin.Available online http://breast-cancer-research.com/content/4/6/R12 Abstract Background: Environmental persistent organochlorines (POCs) biomagnify in the food chain, and the chemicals are suspected of being involved in a broad range of human malignancies. It is speculated that some POCs that can interfere with estrogen receptor-mediated responses are involved in the initiation and progression of human breast cancer. The tumor suppressor gene BRCA1 plays a role in cell-cycle control, in DNA repair, and in genomic stability, and it is often downregulated in sporadic mammary cancers. The aim of the present study was to elucidate whether POCs have the potential to alter the expression of BRCA1. Methods: Using human breast cancer cell lines MCF-7 and MDA-MB-231, the effect on BRCA1 expression of chemicals belonging to different classes of organochlorine chemicals (the pesticide toxaphene, 2,3,7,8-tetrachlorodibenzo-p-dioxin, and three polychlorinated biphenyls [PCB#138, PCB#153 and PCB#180]) was measured by a reporter gene construct carrying 267 bp of the BRCA1 promoter. A twofold concentration range was analyzed in MCF-7, and the results were supported by northern blot analysis of BRCA1 mRNA using the highest concentrations of the chemicals. Results: All three polychlorinated biphenyls and 2,3,7,8-tetrachlorodibenzo-p-dioxin reduced 17β-estradiol (E2)-induced expression as well as basal reporter gene expression in both cell lines, whereas northern blot analysis only revealed a downregulation of E2-induced BRCA1 mRNA expression in MCF-7 cells. Toxaphene, like E2, induced BRCA1 expression in MCF-7.Conclusion: The present study shows that some POCs have the capability to alter the expression of the tumor suppressor gene BRCA1 without affecting the cell-cycle control protein p21 Waf/Cip1 . Some POCs therefore have the potential to affect breast cancer risk.

Determination of the crystal structure of the ternary complex formed between elongation factor Tu:GTP and aminoacylated tRNA revealed three regions of interaction between elongation factor Tu and tRNA. The structure indicates that the conserved glutamic acid at position 271 in Thermus aquaticus EF-Tu could be involved in the binding of the 3' CCA-Phe end of the aminoacylated tRNA. Therefore, the corresponding residue, Glu259, of Escherichia coli EF-Tu was mutated into alanine, aspartic acid, glutamine and tyrosine, in order to substantiate the crystallographic structural evidence and to obtain further knowledge of the importance of this residue. All of the mutated proteins showed nucleotide binding properties similar to the wild type. In addition the GTPase activities were similar to the wild type. The mutation of Glu259 to either alanine or aspartic acid resulted in a reduced strength of interaction with tRNA, while mutation to tyrosine abolished completely the interaction with tRNA. Finally, mutation to glutamine resulted in an elongation factor Tu variant behaving like the wild type. In conclusion, the environment around the site binding the CCA-Phe end of the tRNA is very restricted spatially and chemically so that only a residue with almost the same size and chemical properties as glutamic acid fulfils the requirements with regard to size, salt bridge-formation potential and maintenance of the backbone conformation at the 259 position.

The recently solved structure of the ternary complex formed between GTP-bound elongation factor Tu and aminoacylated tRNA reveals that the elements of aminoacyl-tRNA that interact with elongation factor Tu can he divided into three groups: the T stem: the 3'-end CCA-Phe; and the 5' end. The conserved residues Arg2X8, LysX9 and Asn90 are involved in the binding of the 5' end. In the active, GTP-bound form of the elongation factor, Arg288 and Am90 are involved in the forination of a network of hydrogen bonds connecting the switch regions I and I1 of domain 1 with the rest of the molecule. This network is disrupted upon formation of the ternary complex. Arg288 was replaced by alanine, isoleucine, lysine or glutamic acid, and the resulting mutants have been subjected to an in vitro characterisation with the aim of clarifying the function of Arg288. Unexpectedly, the mutants behaved like the wild-type factor with regard to thc association and dissociation o f guanine nucleotides, and the intrinsic GTPasc activities are unchanged. Furthermore, the mutants were as efficient as the wild-type factor i n carrying out protein synthesis in vitro in the presence of an excess of aminoacyl-tRNA. However. the mutants' abilities to bind aminoacyl-tRNA and protect the labile arninoacyl bond were impaired, especially where the charge had been reversed.