Increase in the estrogen binding capacity of breast cancer cytosols following limited proteolysis with trypsin

Abstract

When small amounts of trypsin were added to prelabelled estrogen receptors in 24 human breast cancer cytosols there was a substantial increase in the binding capacity [79 ± 11 (SE) %]. At the same time the affinity of the hormone receptor interaction was maintained at a very high level or even increased. This finding is discussed in relation to previous results where a diisopropylfluorophosphate (DFP) inhibitable protease activity was shown to cause a similar augmentation of estrogen binding sites in human myometrial cytosols. Addition of sodiummolybdate at or immediately after homogenization led to a similar increase in estrogen binding sites. Because these two effects were not additive we propose that the limited trypsin treatment reactivates the binding sites previously inactivated through a mechanism which can be inhibited by sodiummolybdate.