Phosphorylation of Estradiol Receptor on Tyrosine and Interaction of Estradiol and Glucocorticoid Receptors with Antiphosphotyrosine Antibodies
Phosphorylation of proteins on tyrosine is a recent finding; it is a rare event and seems to be related to growth factor induced cell multiplication, cell transformation(1) and to cell differentiation(2). Several protein-tyrosine kinases are associated to peptide growth factor receptors, the products of several retroviral oncogenes are endowed witn protein-tyrosine kinase activity(3). Although reversible phosphorylation of proteins on tyrosine is thought to modulate the function of proteins. tyrosine kinase substrates are still elusive. The only exception found so far, to our knowledge, is the estradiol receptor. Work from our laDoratory has shown that phosphorylation on tyrosine of this receptor endows the receptor with hormone binding activity(4,5). Nuclei of mouse and calf estrogen target tissues contain an enzyme that inactivates the hormone binding of estradiol-occupied as well as hormone-free receptor (6,7). Preliminary characterization of this enzyme after its partial purification suggested, but did not prove, that it is a phosphatase wich acts directly on the receptor(7). Subsequently direct evidence of this point was given(8).
KeywordsGlucocorticoid Receptor Hormone Binding Estradiol Receptor Receptor Preparation Antiphosphotyrosine Antibody
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