We have previously detected an MMTV env gene-like 660 bp sequence in 38% of human breast cancers, but not in normal tissues or other tumors. In this communication we report the sequences from eleven tumors and three breast cancer cell lines, and compare them to four strains of MMTV and to the known endogenous retroviral sequences. The breast cancer sequences were highly homogenous to the MMTV's, but not to the endogenous sequences suggesting an exogenous origin.

Estrogens, whether natural or synthetic, clearl inluence reproductive development, senescence, and carcinogenesis. Pyrethroid insecticides are now the most widely used agents for indoor pest control, providing potential for human exposure. Using the MCF-7 human breast carcinoma cel line, we stdied the estrogenic potential of several sthetic pyrethroid mpounds in vitro usig pS2 mRNA levels as the end point. We tested sumitin, tfenvalerate trans alletbrin, and permethrin. Nanomolar concentrations of either sumithin or fenvalerate were sufficient to increase pS2 expression slighdy above basal levels. At micromolar concentmtions, these two pyrethroid compounds induced pS2 expression to levels comparable to those elicited by 10 nM 17f.estradiol (fivefold). The estrogenic activity of sumithrin was abolished with co-treatment with an antiestrogen (ICI 164,384), whereas estrogenic activity of fenvalerate was not si y diminished with antiestrogen co-treatment. In addition, both sumithini and fenvalerate were:able to induce ei proliferation of MCF-7 cells in a se-response fashion. Neither perm in nor d-trans allethrin affected pS2 expression. Perme had a noticeable effect on cel proliferation at 100 pM, whereas d-trans allethin slightdy induced MCF-7 cell prolieration at 10 pM, but was toxic at higher concentrtions. Overall, our studies imply that each pyrethroid compound is unique in its ability to influence several cellular pathways. These finding sugget that pyrethroids should be considered to be hormio disrunptors, and ther potentidal to affect edocrine fimction n' human and widlif should be inivestigated. Key word 173-estradiol, MCF-7 human breast carcinoma cells, pS2, pyrethroid, RNA.

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