PubMed Health⌕ Search

Biomedical subjects

J A Kassis

Publications and source records attributed to J A Kassis.

24 records · Page 2Linked to original sources
PubMed1984

Primary cultures of estrogen-responsive cells from rat uteri: induction of progesterone receptors and a secreted protein.

Uterine cells from immature rats can be grown in culture, are estrogen responsive, and contain estrogen receptors. Progesterone receptor is induced within 1 day of 17 beta-estradiol treatment, with maximal response occurring after 2 days of treatment (300-500% of the control value). Induction of progesterone receptor occurred at physiological 17 beta-estradiol concentrations, with half-maximal response at about 5 X 10(-11) M. 17 beta-Estradiol induced the synthesis of a secreted protein (mol wt, 130,000) in a dose-dependent fashion. This 130-K protein was also induced by 16 alpha-estradiol (1-10 nM), but not by progesterone (10 nM), testosterone (1 nM), or dexamethasone (1 nM). Examination of the estrogen-binding properties of the cultured cells shows a saturable binding site (Kd approximately 10(-10) M) which can be translocated to the nucleus. Estrogen receptors were maintained at in vivo levels as uterine cells proliferated throughout 10 days of culture. This was in contrast to estrogen receptor levels in Fischer 344 rat pituitary cell cultures, which dropped off drastically on a DNA basis as cells proliferated. These studies indicate that estrogen receptor-containing rat uterine cells proliferate and are responsive in primary cell cultures.

Animals↗
PubMed1984

Estrogen receptors in rat uterine cell cultures: effects of medium on receptor concentration.

Both the estrogen responsiveness and -binding capacity of cultured rat uterine cells were decreased dramatically when the medium was not changed at 24-h intervals. Treatment of cells for 24 h with 1 nM 17 beta-estradiol in fresh medium led to a 3-fold increase in progesterone receptor concentration, but without fresh medium, no increase in progesterone receptors was observed. When the medium was changed on cells with a low estrogen-binding capacity (depleted cells), a 6- to 10-fold increase in estrogen-binding capacity (to in vivo levels) occurred within 24 h (fed cells), and total protein was increased 2-fold. The high and low affinity binding characteristics of fed and depleted cells were identical. Recovery of the estrogen-binding capacity of depleted cells was relatively slow, increasing after a 6-h lag and reaching maximal levels by 24 h. While 6 h of 10(-5) M cycloheximide treatment (protein synthesis inhibited greater than 95%) had little effect on control estrogen binding levels, it completely inhibited the increase in the estrogen-binding capacity induced by changing the medium on depleted cells. These results indicate that estrogen-binding activity can be varied in cultured rat uterine cells by changing medium conditions and suggest that these changes are due to differences in receptor protein levels and not to a receptor activation-inactivation phenomenon.

Animals↗
PubMed1983

On the mechanism of estrogen receptor replenishment: recycling, resynthesis and/or processing.

Estrogen receptor replenishment has been extensively studied after a single injection of estradiol-17 beta in the rat. Most studies indicate that replenishment, under these conditions, is due both to recycling and to resynthesis of receptor. In the case of short-acting estrogens, total replenishment occurs in the absence of protein synthesis and loss of nuclear receptor closely corresponds to an increase in cytoplasmic receptor. After estradiol-17 beta injection, there is a loss of nuclear receptor without a corresponding increase in cytoplasmic receptor, leading to a loss in total receptor content or 'processing'. Since little processing occurs with the active, short-acting estrogen, we propose that processing is not essential for estrogen action. Evidence is accumulating to indicate that processing may be due to a reversible inactivation of the steroid binding capacity of the receptor. We discuss a model in which there are two routes for replenishment: a simple equilibrium scheme where no processing occurs and a second route where the receptor is processed to a form with low affinity for estrogen which must be reactivated before binding can occur.

Animals↗
PubMed1981

Estrogen receptor replenishment. Evidence for receptor recycling.

Replenishment of uterine estrogen receptor was examined in immature rats following injection of 16 alpha-estradiol. 16 alpha-Estradiol is a "short-acting" estrogen that, after a single injection, stimulates early estrogenic responses (water imbibition, induced protein synthesis, etc.), but not long term responses (DNA synthesis). Replenishment after 16 alpha-estradiol injection was complete within 4 h. Furthermore, disappearance of receptor from the nucleus closely corresponded to a reappearance of receptor in the cytoplasm. In contrast to this, receptor replenishment following injection of 1 microgram of either diethylstilbesterol or 17 beta-estradiol was very slow and lagged behind the disappearance of nuclear receptor, leading to an apparent decrease in total receptor content. Half-lives for the clearance of nuclear estrogen-receptor complexes were estimated to be 30 min for 16 alpha-estradiol and 2 h for 17 beta-estradiol, respectively. Inhibition of protein synthesis by cycloheximide did not inhibit replenishment after 16 alpha-estradiol injection. Studies on replenishment after 17 beta-estradiol injection in the presence of cycloheximide could not be interpreted due to a decrease in total receptor content caused by long term cycloheximide treatment. Multiple injections of 17 alpha-estradiol did not lead to a lag in replenishment time or a decrease in total receptor content. This represents a case in which estrogen receptor replenishment appears to be due entirely to receptor recycling.

Animals↗
PubMed1978

Pyridoxine kinase in Plasmodium lophurae and duckling erythrocytes.

Pyridoxine kinase enzyme activity was greatly increased in duckling erythrocytes infected with Plasmodium lophurae. Pyridoxine kinase activity in parasites freed from erythrocytes was much greater than that of uninfected erythrocytes. The apparent Km for pyridoxine of the parasite enzyme was 6.6 times 10(-5) M whereas the host red cell enzyme Km was 1.9 times 10(-6) M. Deoxypyridoxine inhibited host and parasite pyridoxine kinase activity with an apparent Ki of 1.5 times 10(-6) and 8.6 times 10(-6) M, respectively. These results suggest that the vitamin B6 metabolism of the malaria parasites is distinct and separate from that of the host erythrocytes.

Adenosine Triphosphate↗