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Hormone‐dependent processing of the avian progesterone receptor
Author(s) -
Sullivan William P.,
Smith David F.,
Beito Thomas G.,
Krco Christopher J.,
Toft David O.
Publication year - 1988
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.240360202
Subject(s) - progesterone receptor , cytosol , receptor , oviduct , hormone receptor , phosphorylation , biology , insulin like growth factor 1 receptor , hormone , medicine , endocrinology , nuclear receptor , chemistry , biochemistry , estrogen receptor , enzyme , growth factor , transcription factor , cancer , breast cancer , gene
Abstract Avian progesterone receptor exists as two forms, A and B, with molecular weights of 79,000 and 110,000 daltons, respectively. The origin and significance of these two forms is an area of active investigation and debate. Monoclonal antibodies produced against these two forms were used to examine receptor stability in cytosol and changes in the receptor forms induced by hormone binding. The lability of hormone binding at elevated temperatures is well documented. Analysis by Western blotting showed the receptor was stable in freshly prepared oviduct cytosol for 2 hr at 37°C, while hormone binding was lost within 30 min. However, loss of receptor through degradation was seen when cytosol was prepared from frozen tissue or when homogenization was excessive. Progesterone was injected into diethylstilbestrol‐stimulated chicks to examine, in vivo, effects of hormone treatment on receptor forms in the cytosol and nuclear fractions. Progesterone treatment caused a time‐ and dose‐dependent conversion of the A receptor to a form (A′) with a slower electrophoretic mobility. The cytosolic progesterone receptor was divided equally between the B and A forms, while the nuclear receptor was predominantly A′. The amount of nuclear receptor was consistently less than cytosolic receptor. Receptor phosphorylation was analyzed by incubating tissue minces with [ 32 P]orthophosphate with or without progesterone followed by immune isolation of receptor forms. Progesterone treatment caused a time‐dependent increase in cytosol receptor phosphorylation which was evident after 5 min of treatment. This phosphorylation was observed with both the A and B receptor forms. The results indicate that receptor phosphorylation is a very early event during progesterone action.