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Transformation of Chick Oviduct Progesterone Receptor in Vitro: Effects of Hormone, Salt, Heat, and Adenosine Triphosphate^*

Department of Biological Sciences, Oakland University Rochester, Michigan 48063;
Lab Hormones (INSERM U33) 94270 Bicetre, France

Address all correspondence and requests for reprints to: Dr. V. K. Moudgil, Biological Sciences, Oakland University, Rochester, Michigan 48063.

Abstract

Effects of salt, heat, and ATP on the rate of sedimentation of chick oviduct progesterone receptor (PR) were examined under various conditions. Cytosol [3H]PR complex (PRc) sedimented as an 8S molecule in 10-35% glycerol or 5- 20% sucrose gradients. Incubation of the oviduct cytosol containing [³H]PRc at either 23 or 0 C with 0.3 M KC1 or 5-10 mM ATP for 1-4 h resulted in the appearance of a slower migrating form with a sedimentation rate of approximately 4S and a complete and concomitant disappearance of the 8S PR form. This transformation of the receptor was inhibited by molybdate and paralleled an increase in the affinity of the cytosol PRc toward DNA-cellulose, ATP-Sepharose, and isolated nuclei. The 8S to 4S transformation of PR could be achieved with the unliganded receptor. The effect of the hormone on the rate of the transformation of PR was examined. A gradual transformation of the 8S PR occurred with increasing time of incubation at 23 or 0 C with KC1 or with 10 mM ATP. The ATP-induced transformation of the 8S form was complete by 2-4 h in both the presence and absence of progesterone. The transformation of PR by salt was complete by 1-2 h of incubation of the cytosol with 0.3 M KC1 at 0 C and was slightly accelerated in the presence of the steroid. However, when the cytosol PR was thermally transformed by incubation at 23 C, the appearance of the 4S PR form was significantly accelerated in the presence of the hormone. While the addition of 10 mM ATP to the incubation mixture enhanced the rate of transformation of PRc by heat and salt, lower nucleotide concentrations (0.1-2 mM) inhibited the thermal conversion of the 8S PR (in both its liganded and unliganded forms) to the 4S form. In addition, other nucleoside triphosphates (CTP, GTP, and UTP) were also effective in inducing the 8S to 4S transformation of the unoccupied and the steroid-bound PR. The transforming effects of heat, salt, and ATP were cumulative, and a complete 8S to 4S transformation could be achieved within 5 min when all three were applied simultaneously. We conclude that ATP and other nucleoside triphosphates are effective modifiers of the process of transformation of the chick oviduct PR in vitro. The transformation of PR in vitro can be induced in the absence of the hormone, but it is accompanied by a significant loss (about one third) of steroid-binding capacity in the case of incubation at 23 C or with ATP (at 0 C). The presence of hormone significantly accelerates the process of heat transformation of PR. (Endocrinology 116: 1267-1274,1985)

Footnotes

^* This work was supported by NIH Grant AM-20893 and INSERM Republique Francaise).

Received July 23, 1984.

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