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L Y Yu

Publications and source records attributed to L Y Yu.

22 records · Page 2Linked to original sources
PubMed1977

Glucocorticoid induction of growth hormone synthesis in a strain of rat pituitary cells.

Conditions were determined for measuring growth hormone synthesis by a clonal strain of rat pituitary cells grown in suspension culture. Incubation of the cells with [3H]leucine in either continuous labeling or pulse-chase experiments showed that secretion of newly synthesized growth hormone commences only after a lag of about 15 min. The pulse-chase experiments also demonstrated that there is no detectable degradation by the cells of growth hormone. Thus growth hormone synthesis could be measured, in the absence of complications arising either from secretion or degradation of growth hormone, by incubating the cells with [3H]leucine for 10 min. Exposure of cells grown under the usual culture conditions to dexamethasone (a synthetic glucocorticoid) led to an average stimulation of specific growth hormone synthesis (growth hormone synthesis/total cytoplasmic protein synthesis) of only 2.6-fold. However, two other growth conditions were found in which dexamethasone routinely yielded a 5- to 15-fold stimulation of specific growth hormone synthesis. One of these conditions, involving substitution of 10% fetal calf serum for the normal serum supplement, was employed in subsequent experiments. A stimulation of specific growth hormone synthesis could be observed at 10(-9) M dexamethasone, and the maximum stimulation was observed at dexamethasone concentrations of about 10(-8) to 10(-7) M. There was a lag of about 6 h before a stimulation by dexamethasone of specific growth hormone synthesis was detected. Thereafter, the stimulation increased in a nearly linear fashion until maximum stimulation was reached at about 48 h.

Animals↗
PubMed1977

Pregrowth hormone messenger RNA: glucocorticoid induction and identification in rat pituitary cells.

We have investigated whether the large (5- to 15-fold) stimulation of synthesis of growth hormone (somatotropin) observed upon exposure of a strain of rat pituitary (GH3) cells to dexamethasone (a synthetic glucocorticoid) arises from a stimulation of pregrowth hormone mRNA. A good agreement was observed between the stimulation of growth hormone synthesis and the stimulation of cytoplasmic levels of pregrowth hormone mRNA, assayed by translation in wheat germ extracts. Electrophoresis on formamide-acrylamide gels of oligo(dT)-treated membrane fraction RNA revealed a band that was induced by dexamethasone to about the same extent as was translatable pregrowth hormone mRNA. Elution of the band and translation in wheat germ extracts showed directly that it contained pregrowth hormone mRNA. These results suggest that the dexamethasone induction of growth hormone synthesis in GH3 cells arises from an accumulation of pregrowth hormone mRNA in the cytoplasm of the cells. The pregrowth hormone mRNA band observed by gel electrophoresis had an estimated molecular weight of 3.6 X 10(5), suggesting the existence in this molecule of an untranslated region at least 200 nucleotides in length.

Cell Line↗