I would like to know if murine estrogen crosses with human estrogen receptor (alpha and beta) in vivo. I know that ER+ breast cancer cell lines need estrogen pellets to grow but is it because mice don't product enough estrogen or because murine estrogen has no effect?
The estradiol is exactly the same, human or mouse. The pattern of metabolites will differ between the species, but "mouse estradiol" definitely interacts with human ER.
You usually have to place estradiol pellets in mice to augment their natural cycles. Female mice do not cycle uniformly and not at all for many strains unless exposed to males. Just like humans, estrogen levels are dependent upon where in the estrus cycle one finds the mouse. Estrogen levels are very low at the start of a cycle and peak just before ovulation and then are intermediate until menses. So, hormone dependent tumors require supplementation to overcome this issue of cycling estrogen levels. Dr. Roy is also correct, the estradiol is the same between species and mouse estradiol will activate human ER.
The reason exogenous estrogens need to be added to allow ER+ tumors xenografts to grow is that athymic/nude mice have an ovarian deficiency and produce very low levels of estrogens. This is one reason why they are sterile and need to be generated by crossing heterozygotes. In studies directly measuring subtle effects of estrogens and/or antiestrogens on tumor growth, many investigators will remove the ovaries in order to bring this levels as close as possible to zero. Even though the endogenous levels are not typically sufficient to stimulate optimal growth they can be high enough to subtly effect tumor growth rates.
Actually I'm also confronted with this problem. Maybe you can recommend me some literature on the reactivity of murine estrogen with human estrogen receptors ?
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