The Biochemical Mechanisms of the Stimulating Action of Estradiol on the Growth of Mammary Tumours1)

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Abstract
The mechanisms of stimulating effect of estradiol on the growth of hormone-dependent mammary tumours in experimental animals were studied. Estradiol receptors were detected in plasmatic membranes of estradiol-dependent tumour cells. Estradiol-independence of tumours was found to be a result of the impairment of the estradiol receptors in the plasmatic membranes, intra-cellular receptors, or of their ability to interact with the chromatin of the target cells. It was shown that the interaction of receptors of plasmatic membranes of hormone-dependent tumour cells with estradiol results in activation of the membrane adenylate cyclase and in a short-term rise of a cAMP content. A treatment of the hormone-dependent tumours with ovarian hormones brings about an increase in the activity of the cAMP-dependent protein kinases in cell nuclei, which points to their translocation from cytosol. Under effect of estradiol the phosphorylation of nuclear proteins at the serine, threonine and tyrosine residues increases.