Bromoergocryptine-induced prolactin degradation in cultured pituitary cells

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Abstract

Continuous labeling of pituitary cells with [3H]-leucine resulted in a linear accumulation of [3H]prolactin in control cultures, but in bromoergocryptine (CB-154) treated cultures the rate of [3H]prolactin accumulation decreased with time. The possibility that this decreased accumulation of labeled prolactin was due to CB-154-induced prolactin degradation was examined by incubating cells for 30 min with [3H]leucine followed by incubation in a chase medium containing a 400-fold excess of unlabeled leucine. In control cultures, there was little degradation of [3H] prolactin over a 24-h period. In cultures containing CB-154 in the chase incubation medium, there was a 22% decrease in labeled prolactin after 8 h and a 50% decrease after 24 h. Pretreatment of cells with CB-154 for 24 h before pulse-chase analysis resulted in a greater rate of prolactin degradation than was observed in cells treated with CB-154 during the chase incubation only. CB-154 treatment did not affect the degradation of nonprolactin proteins, demonstrating the specificity of its effects. Cycloheximide did not affect prolactin degradation in CB-154-pretreated cells; however, cycloheximide blocked the ability of CB-154 to induce prolactin degradation when the two drugs were added simultaneously. The relationship between prolactin synthesis and degradation was examined in cells treated for varying times with CB-154 and then pulsed for 30 min with [3H]leucine followed by a 4-h chase incubation. Prolactin synthesis declined sharply after 1-2 days of CB-154 treatment and reached a new plateau of 22% of control values after 4 days of treatment. Prolactin degradation was maximal after 1 day of CB-154 treatment and returned toward control values after 3-4 days of treatment. Lysosomes are likely involved in CB-154-induced prolactin degradation as chloroquine is able to partially block CB-154 effects. These studies suggest that CB-154 is able to induce substantial prolactin degradation. Thus, prolactin degradation is involved in removal of excess prolactin which accumulates in the pituitary when prolactin secretion is inhibited.

Original languageEnglish (US)
Pages (from-to)3573-3578
Number of pages6
JournalBiochemistry
Volume19
Issue number15
StatePublished - 1980
Externally publishedYes

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Bromocriptine
Prolactin
Cultured Cells
Degradation
Leucine
Cycloheximide
Chloroquine
Lysosomes
Labeling
Proteolysis

ASJC Scopus subject areas

  • Biochemistry

Cite this

Bromoergocryptine-induced prolactin degradation in cultured pituitary cells. / Maurer, Richard.

In: Biochemistry, Vol. 19, No. 15, 1980, p. 3573-3578.

Research output: Contribution to journalArticle

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abstract = "Continuous labeling of pituitary cells with [3H]-leucine resulted in a linear accumulation of [3H]prolactin in control cultures, but in bromoergocryptine (CB-154) treated cultures the rate of [3H]prolactin accumulation decreased with time. The possibility that this decreased accumulation of labeled prolactin was due to CB-154-induced prolactin degradation was examined by incubating cells for 30 min with [3H]leucine followed by incubation in a chase medium containing a 400-fold excess of unlabeled leucine. In control cultures, there was little degradation of [3H] prolactin over a 24-h period. In cultures containing CB-154 in the chase incubation medium, there was a 22{\%} decrease in labeled prolactin after 8 h and a 50{\%} decrease after 24 h. Pretreatment of cells with CB-154 for 24 h before pulse-chase analysis resulted in a greater rate of prolactin degradation than was observed in cells treated with CB-154 during the chase incubation only. CB-154 treatment did not affect the degradation of nonprolactin proteins, demonstrating the specificity of its effects. Cycloheximide did not affect prolactin degradation in CB-154-pretreated cells; however, cycloheximide blocked the ability of CB-154 to induce prolactin degradation when the two drugs were added simultaneously. The relationship between prolactin synthesis and degradation was examined in cells treated for varying times with CB-154 and then pulsed for 30 min with [3H]leucine followed by a 4-h chase incubation. Prolactin synthesis declined sharply after 1-2 days of CB-154 treatment and reached a new plateau of 22{\%} of control values after 4 days of treatment. Prolactin degradation was maximal after 1 day of CB-154 treatment and returned toward control values after 3-4 days of treatment. Lysosomes are likely involved in CB-154-induced prolactin degradation as chloroquine is able to partially block CB-154 effects. These studies suggest that CB-154 is able to induce substantial prolactin degradation. Thus, prolactin degradation is involved in removal of excess prolactin which accumulates in the pituitary when prolactin secretion is inhibited.",
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