Estrogen receptor cleavage and plasminogen activation by enzymes in human breast tumor cytosol
Abstract
Estrogen receptors in cytoplasmic extracts of breast tumors from more than 40 patients were separately analyzed by gel filtration and/or ultracentrifugation under diverse conditions. Resultant patterns are presented for specimens from 11 women with infiltrating duct carcinoma and are representative of results obtained in all samples of sufficient size and receptor content (approximately 40 fmol/mg cytosol protein) for accurate determination of hydrodynamic parameters. Estradiol-binding components of intracellular origin were distinguished from the serum contaminant, sex hormone-binding globulin by their high affinity for diethylstilbestrol and negligible affinity for 5 alpha-dihydrotestosterone. The predominant molecular forms of the receptors, but not the steroid specificity, varied dramatically with experimental factors, including the duration of the fractionation procedure, ionic strength, and the presence of protease inhibitors, particularly the bacterial tripeptides N-acetyl- and N-propionyl-L-leucyl-L-leucyl-DL-arginine aldehydes (leupeptin). At least three discrete forms of the intracellular receptors were detected. The smallest labeled complex, the mero-receptor, with a sedimentation coefficient of about 3S and a Stokes...Continue Reading
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