The effects of epidermal growth factor on cell proliferation and prolactin production by GH3 rat pituitary cells

ABSTRACT To gain insight into the mechanism underlying the epidermal growth factor (EGF)-induced changes in responsiveness to TRH and in the numbers of TRH receptors (TRH-Rs) in the pituitary, we investigated the transcriptional regulation by EGF of the TRH-R gene in GH4C1 cells. Northern blot analyses and binding studies revealed that EGF reduced both TRH binding and TRH-R mRNA levels in a dose- and time-dependent manner, while no significant changes were observed in β-actin mRNA levels. Addition of actinomycin D caused an acute increase in the basal TRH-R mRNA level, and the rate of decrease of the TRH-R mRNA was identical in control and EGF-treated groups, suggesting that the stability of the TRH-R mRNA was not significantly affected in EGF-treated cells. Incubation with cycloheximide also induced an increase in the basal TRH-R mRNA level and completely reversed the EGF-induced reduction of TRH-R mRNA levels. Furthermore, a nuclear run-on assay demonstrated that the rate of transcription of the TRH-R gene was significantly inhibited in cells treated with EGF. We conclude that (1) EGF decreases the expression of the TRH-R mRNA largely by reducing its rate of transcription, and this action requires the synthesis of new proteins, and (2) inhibitors of protein and RNA synthesis cause a significant increase in the basal TRH-R mRNA level, suggesting that there may be a short-lived protein suppressing the TRH-R mRNA level in the pituitary.

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Receptor-bound somatostatin and epidermal growth factor are processed differently in GH4C1 rat pituitary cells.

The Journal of Cell Biology ◽

10.1083/jcb.102.3.878 ◽

1986 ◽

Vol 102 (3) ◽

pp. 878-888 ◽

Cited By ~ 21

Author(s):

D H Presky ◽

A Schonbrunn

Keyword(s):

Growth Factor ◽

Epidermal Growth Factor ◽

Cell Surface ◽

Acid Treatment ◽

Biological Effects ◽

Membrane Receptors ◽

Pituitary Cells ◽

Rat Pituitary ◽

Epidermal Growth ◽

Initial Binding

GH4C1 cells, a clonal strain of rat pituitary tumor cells, have high-affinity, functional receptors for the inhibitory hypothalamic peptide somatostatin (SRIF) and for epidermal growth factor (EGF). In this study we have examined the events that follow the initial binding of SRIF to its specific plasma membrane receptors in GH4C1 cells and have compared the processing of receptor-bound SRIF with that of EGF. When cells were incubated with [125I-Tyr1]SRIF at temperatures ranging from 4 to 37 degrees C, greater than 80% of the specifically bound peptide was removed by extraction with 0.2 M acetic acid, 0.5 M NaCl, pH 2.5. In contrast, the subcellular distribution of receptor-bound 125I-EGF was temperature dependent. Whereas greater than 95% of specifically bound 125I-EGF was removed by acid treatment after a 4 degrees C binding incubation, less than 10% was removed when the binding reaction was performed at 22 or 37 degrees C. In pulse-chase experiments, receptor-bound 125I-EGF was transferred from an acid-sensitive to an acid-resistant compartment with a half-time of 2 min at 37 degrees C. In contrast, the small amount of [125I-Tyr1]SRIF that was resistant to acid treatment did not increase during a 2-h chase incubation at 37 degrees C. Chromatographic analysis of the radioactivity released from cells during dissociation incubations at 37 degrees C showed that greater than 90% of prebound 125I-EGF was released as 125I-tyrosine, whereas prebound [125I-Tyr1]SRIF was released as a mixture of intact peptide (55%) and 125I-tyrosine (45%). Neither chloroquine (0.1 mM), ammonium chloride (20 mM), nor leupeptin (0.1 mg/ml) increased the amount of [125I-Tyr1]SRIF bound to cells at 37 degrees C. Furthermore, chloroquine and leupeptin did not alter the rate of dissociation or degradation of prebound [125I-Tyr1]SRIF. In contrast, these inhibitors increased the amount of cell-associated 125I-EGF during 37 degrees C binding incubations and decreased the subsequent rate of release of 125I-tyrosine. The results presented indicate that, as in other cell types, EGF underwent rapid receptor-mediated endocytosis in GH4C1 cells and was subsequently degraded in lysosomes. In contrast, SRIF remained at the cell surface for several hours although it elicits its biological effects within minutes. Furthermore, a constant fraction of the receptor-bound [125I-Tyr1]SRIF was degraded at the cell surface before dissociation. Therefore, after initial binding of [125I-Tyr1]SRIF and 125I-EGF to their specific membrane receptors, these peptides are processed very differently in GH4C1 cells.

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Novel Pituitary Actions of Epidermal Growth Factor: Receptor Specificity and Signal Transduction for UTS1, EGR1, and MMP13 Regulation by EGF

International Journal of Molecular Sciences ◽

10.3390/ijms20205172 ◽

2019 ◽

Vol 20 (20) ◽

pp. 5172 ◽

Cited By ~ 1

Author(s):

Qiongyao Hu ◽

Shaohua Xu ◽

Cheng Ye ◽

Jingyi Jia ◽

Lingling Zhou ◽

...

Keyword(s):

Signal Transduction ◽

Cell Proliferation ◽

Growth Factor ◽

Epidermal Growth Factor ◽

Mrna Expression ◽

Grass Carp ◽

Pituitary Cells ◽

Dependent Manner ◽

Receptor Specificity ◽

Epidermal Growth

Epidermal growth factor (EGF) is a member of the EGF-like ligands family, which plays a vital role in cell proliferation, differentiation, and folliculogenesis through binding with EGF receptors, including ErbB1 (EGFR/HER1), ErbB2 (HER2), ErbB3 (HER3), and ErbB4 (HER4). In mammals, many functional roles of EGF have been reported in the ovaries and breasts. However, little is known about the functions of EGF in the pituitary, especially in teleost. In this study, using grass carp pituitary cells as the model, we try to examine the direct pituitary actions of EGF in teleost. Firstly, transcriptomic analysis showed that 599 different expressed genes (DEGs) between the control and EGF-treatment group were mainly involved in cell proliferation, cell migration, signal transduction, and transcriptional regulation. Then, we further confirmed that EGF could significantly induce UTS1, EGR1, and MMP13 mRNA expression in a time-and dose-dependent manner. The stimulatory actions of EGF on UTS1 and EGR1 mRNA expression were mediated by the MEK1/2/ERK1/2 and PI3K/AKT/mTOR pathways coupled with both ErbB1 and ErbB2 in grass carp pituitary cells. The receptor specificity and signal transductions for the corresponding responses on MMP13 mRNA expression were also similar, except that the ErbB2 and PI3K/AKT/mTOR pathway were not involved. As we know, MMP13 could release EGF from HB-EGF. Interestingly, our data also showed that the MMPs inhibitor BB94 could suppress EGF-induced UTS1 and EGR1 mRNA expression. These results, taken together, suggest that the stimulatory actions of EGF on UTS1 and EGR1 mRNA expression could be enhanced by EGF-induced MMP13 expression in the pituitary.

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