These studies were done in Gwen V. Childs, Ph.D.'s laboratory; University of Texas Medical Branch , Galveston, TX. Dr. Childs is now at the University of Arkansas for Medical Sciences.
They focus on the significance of Epidermal growth factor (EGF) found in the anterior pituitary cells. They involve experiments designed to test the extent to which EGF is involved in stress responses. In this group of studies, we tested its ability to regulate pituitary corticotropes.
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- Is EGF a secretagogue for corticotropes?
- Does EGF stimulate differentiation of corticotropes?
- Is EGF a mitogen for corticotropes?
- Effect of stress on pituitary EGF.
- Recent publications describing these studies.
Is EGF a secretagogue for corticotropes?
Epidermal growth factor (EGF) has been detected in the anterior pituitary, however the early studies did not know its specific function. We began studies of its significance by testing whether or not EGF could stimulate release of adrenocorticotropin from the anterior pituitary. We learned that EGF alone stimulates secretion of adrenocorticotropin (ACTH) from pituitary corticotropes. It also enhances the stimulatory effects of the neuropeptide secretagogue for corticotropes, corticotropin releasing hormone (CRH). These data suggest that it is a secretagogue for corticotropes Back to Menu
Does EGF stimulate differentiation of corticotropes?
We stimulated anterior pituitary cells for 4 h with EGF with and without CRH to learn if EGF alone increased the number of corticotropes. The corticotropes were detected by immunocytochemical label for adrenocorticotropin (ACTH). The above figure shows that EGF alone stimulated increases in percentages of ACTH cells (double small stars). CRH alone also stimulates more ACTH-bearing cells. (single small stars). EGF also enhances the stimulatory effects of 0.5 nM CRH (large star).
We also tested the effect of EGF on expression of pro-opiomelanocortin mRNA (POMC) detected by in situ hybridization. The following figure shows that EGF alone stimulates more cells that express POMC mRNA (small double stars). CRH also stimulates more POMC mRNA-bearing cells (small single star). It also adds to the stimulatory effects of CRH (large star). Thus, it may be both a secretagogue and may stimulate differentiation of cells with the potential to become corticotropes.
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Is EGF a mitogen for corticotropes?
To test its mitogenic potency, we studied EGF effects on populations of corticotropes enriched to 90% by counterflow centrifugation . The cells were grown in microwells for 3-5 days. They were then exposed to bromodeoxyuridine (BrDU) for 1 h. This compound is taken up by dividing cells during DNA synthesis (the S phase of the cell cycle). It was then detected by enzyme immunoassay in the populations of cells grown in micowells. The above figure shows that, after 5 days of culture, both EGF and CRH stimulated increased uptake of BrDU. These data suggest that both are mitogenic.
However, we needed to prove that the BrDU is indeed taken up by dividing corticotropes. Therefore, we used dual-labeling immunocytochemistry to detect BrDU in the nucleus and ACTH in the cytoplasm of the dividing cells. Data are shown in the above figure. As in the Enzyme immunoassays, both EGF and CRH stimulated increased uptake of BrDU and the uptake was indeed in corticotropes. Back to Menu
Effect of stress on pituitary EGF
The next phase of these studies was done by Dr. Xuemo Fan during his Ph.D dissertation research. Dr. Fan tested pituitaries and hypothalami from rats exposed to different stresses for expression of EGF mRNA. He found that cold and restraint stress increased expression of EGF mRNA in the pituitary. However, neither stress changed expression of the same mRNA in the brain.
We were curious about which cell types in the pituitary contained the EGF mRNA. Dr. Fan used dual-labeling in situ hybridization followed by immunocytochemistry to show that that growth hormone cells and gonadotropes (LH and FSH cells) predominated among the cells that expressed EGF mRNA. However, after cold stress, EGF mRNA appeared in both thyrotropes (TSH cells) and corticotropes (ACTH cells). These data are shown in the following graph.
It is interesting to note that corticotropes and thyrotropes are the cell types activated by cold. Thyrotropes stimulate the thyroid and raise metabolic rate while corticotropes respond to stimulate the adrenal to mobilize energy reserves. These data suggest that EGF may be an autocrine regulatory factor for the corticotropes.
Dr. Fan was also able to detect EGF receptors on
corticotropes and thyrotropes. This figure shows the results of dual labeling for EGF
receptor and each of the pituitary hormones. Note that each cell type contains subsets of
cells that express the EGF receptor. Thus, EGF may be a regulatory factor for a number of
pituitary cells. 
Publications describing this work.
- Sasaki, F., Wu, P., Rougeau, D., Unabia, G. and Childs, G.V. Cytochemical studies of responses of corticotropes and thyrotropes to cold and novel environment stress. Endocrinology 127:285-297, 1990.
- Wu, Ping A. and Childs, G.V. Changes in rat pituitary POMC mRNA after exposure to cold or a novel environment detected by in situ hybridization. Journal Histochem Cytochem. 39(6):843-852, 1991.
- Childs, G.V., Patterson, J., Unabia, G., Rougeau, D. and Wu, P. Epidermal growth factor enhances ACTH secretion and expression of POMC mRNA by corticotropes in mixed and enriched cultures. Molecular and Cellular Neurosciences, 2: 235-243 1991.
- Childs, G.V. Structure-function correlates in the corticotropes of the anterior pituitary. Front. Neuroendocrin. 13(3):271-317, 1992.
- Fan, Xuemo, Nagle, G.T., Collins, T.J., and Childs, G.V. 1995 Differential Regulation of EGF and TGF in the rat anterior pituitary and hypothalamus induced by stresses. Endocrinology 136: 873-880.
- Childs, G.V., Rougeau, D., Unabia G. 1995 Corticotropin releasing hormone and epidermal growth factor: mitogens for anterior pituitary corticotropes. Endocrinology 136: 1595-1602.
- Fan, X. and Childs GV 1995. EGF and TGF mRNA and their Receptors in the Rat Anterior pituitary: Localization and Regulation Endocrinology, 136: 2284-2324.
Funding for this work: NSF DCB 9018655 "EGF Modulation of Corticotrope function" 3-15-92--3-31-96.
For more information, contact:
Gwen Childs, Ph.D.,FAAA
Professor and Chair
Department of Neurobiology and Developmental Sciences
University of Arkansas for Medical Sciences
Little Rock, AR 72205
For questions, contact this email address:
