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Gastrin-releasing peptide receptor signaling resulting in growth inhibition
1Department of Protein Biochemistry and Biophysics, Berlex Biosciences, Richmond, California 94804-0099, USA.
Abstract:
We demonstrate that gastrin-releasing peptide (GRP) can inhibit the proliferation of human immortal nontumorigenic (184-B5) mammary epithelial cells ectopically expressing the human GRP receptor. Growth of Balb 3T3 cells ectopically expressing relatively high levels of the GRP receptor was also inhibited by GRP; however, growth of transfectants expressing lower levels of the receptor was not inhibited. Compared with Balb 3T3 cells, mammary epithelial cells could be rendered sensitive to growth inhibition by GRP by the expression of fewer GRP receptors. GRP also stimulated DNA synthesis in quiescent, serum-starved Balb 3T3 transfectants. In clones that were sensitive to growth inhibition by GRP by virtue of their expression of relatively high levels of the GRP receptor, the dose-response curve of GRP-stimulated DNA synthesis was bell shaped. This is consistent with our conclusion that the growth-inhibiting activity of GRP required the activation of a relatively large pool of receptors in Balb 3T3 cells. Significantly, prostaglandin H synthase inhibitors, which block the production of prostaglandins from arachidonic acid, reduced GRP-inhibitory effects on DNA synthesis. We also compared a number of GRP-stimulated signaling pathways in Balb 3T3 clones that were sensitive or insensitive to growth inhibition by GRP, including cAMP formation, phospholipase C activation, calcium mobilization, and arachidonic acid formation. Taken together, these results demonstrate a novel GRP receptor-coupled signal pathway promoting growth inhibition in which prostaglandin H synthase plays a significant role.
Insights
Gastrin-releasing peptide (GRP) inhibits mammary cell proliferation by activating GRP receptors. Prostaglandin H synthase is crucial for this GRP-induced growth inhibition pathway.
Area of Science:
- Cell Biology
- Molecular Biology
- Endocrinology
Background:
- Gastrin-releasing peptide (GRP) is a neuropeptide involved in various physiological processes.
- The role of GRP in regulating cell proliferation, particularly in mammary epithelial cells, requires further elucidation.
- Understanding GRP receptor signaling is key to deciphering its impact on cell growth.
Purpose of the Study:
- To investigate the effect of GRP on the proliferation of human immortal nontumorigenic mammary epithelial cells (184-B5).
- To determine the role of GRP receptor expression levels in mediating GRP's effects on cell growth.
- To identify the signaling pathways coupled to the GRP receptor involved in growth inhibition.
Main Methods:
- Ectopic expression of the human GRP receptor in 184-B5 mammary epithelial cells and Balb 3T3 fibroblasts.
- Assessing cell proliferation and DNA synthesis in response to GRP treatment.
- Analyzing GRP-stimulated signaling pathways, including prostaglandin H synthase activity, cAMP formation, phospholipase C activation, calcium mobilization, and arachidonic acid formation.
Main Results:
- GRP inhibited the proliferation of 184-B5 cells and Balb 3T3 cells expressing high levels of the GRP receptor.
- Mammary epithelial cells required fewer GRP receptors for GRP-induced growth inhibition compared to Balb 3T3 cells.
- Prostaglandin H synthase inhibitors attenuated GRP's inhibitory effects on DNA synthesis, implicating prostaglandins in the pathway.
- A bell-shaped dose-response curve for GRP-stimulated DNA synthesis was observed in sensitive cells, suggesting a requirement for high receptor activation.
Conclusions:
- GRP can inhibit mammary epithelial cell proliferation via a novel receptor-coupled signaling pathway.
- The GRP receptor-mediated growth inhibition is dependent on the level of receptor expression and activation.
- Prostaglandin H synthase plays a significant role in the GRP-induced growth inhibitory signaling cascade.