Wv. Welshons et al., SUBCELLULAR COMPARTMENTALIZATION OF MCF-7 ESTROGEN-RECEPTOR SYNTHESISAND DEGRADATION, Molecular and cellular endocrinology, 94(2), 1993, pp. 183-194
Turnover of the estrogen receptor protein was studied by using enuclea
tion of human breast cancer-derived MCF-7 cells, to examine receptor s
ynthesis and receptor degradation in the separated cytoplasmic compart
ment (cytoplasts) and nuclear compartment (nucleoplasts). Cytoplasts s
ynthesized estrogen receptors as measured by both hormone-binding and
immunoassay, while estrogen receptors (but not progesterone or glucoco
rticoid receptors) were rapidly degraded in nucleoplasts with a half-l
ife of 3-4 h. Little or no degradation of estrogen receptors in cytopl
asts was observed under several conditions. Interestingly, MCF-7 cytop
lasts contained approximately 15% of the cell's estrogen receptors, wh
ich were not 'translocated' by treatment with 17beta-estradiol before
enucleation. We conclude that the estrogen receptor can be synthesized
at least to a hormone binding form in the cytoplasm alone without req
uiring processing in the nucleus, while the nucleus (or perinuclear cy
toplasm) is the primary site of degradation of the estrogen receptor p
rotein. In addition, the presence of a population of estrogen receptor
s that is cytoplasmic but nontranslocatable may need to be considered
in the subcellular localization and actions of steroid receptors.