A Variant Estrogen Receptor Messenger Ribonucleic Acid is Associated with Reduced Levels of Estrogen Binding in Human Mammary Tumors

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Abstract
An analysis of the human estrogen receptor (ER) mRNA was performed on 71 human breast tumors using an RNase protection assay. Complementary DNA clones to the human estrogen receptor (.lambda.R8 and .lambda.R3) were used to generate small antisense 32P-labeled RNA molecules that were hybridized to the tumor RNA. We determined the relative amounts of ER mRNA in each tumor by measuring the amount of RNases A and T1 resistant hybrids. Moreover, because RNase A has the ability to cleave single-base mismatches within RNA/RNA duplexes, we were able to use the assay to screen for possible mutations or deletions in the ER mRNA. A significant correlation was found between the ER mRNA levels and the estrogen binding concentrations determined by a dextran-coated charcoal assay (r = 0.68; P < 0.0001; n = 58). We also identified a subpopulation of tumors in which a mismatch in the ER and mRNA was detected. This message modification, in the B region of the message, significantly correlated with low levels of estrogen binding. This result suggests that the observed B variant might lead to the porduction of receptors with altered properties.