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Phosphatidylinositol 3-kinase mediates heregulin-induced growth inhibition in human epithelial cells
1University of Maryland Cancer Center, Department of Pathology, Baltimore 21201, USA.
Abstract:
Activation of phosphatidylinositol 3-kinase (PI-3K) has been shown to be critical for heregulin induced mitogenesis of human breast epithelial cells. However, the inhibitory effects of HRG have not been linked to PI3K activation. The purpose of these experiments was to determine the effects of heregulin beta 1 (HRG) on growth and PI3K activation of a nonneoplastic human mammary epithelial cell line, 184B5. The results of these experiments indicated that low concentrations of HRG increased the growth of 184B5 cells three fold, while high concentrations inhibited growth by 50%. HRG at all concentrations tested increased tyrosine phosphorylation of erbB3. Similarly, HRG at all concentrations stimulated the association of PI3K with erbB3. Wortmannin, an inhibitor of PI3K enzymatic activity, reversed both the inhibitory and stimulatory effects of HRG on incorporation of [3H] thymidine into DNA. We conclude that both the growth inhibitory and stimulatory effects of HRG in nonneoplastic human mammary epithelial cells are mediated by activation of PI3K.
Insights
Heregulin beta 1 (HRG) differentially affects human mammary epithelial cell growth by activating phosphatidylinositol 3-kinase (PI-3K). Both growth inhibition and stimulation by HRG are mediated through PI-3K activation.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Phosphatidylinositol 3-kinase (PI-3K) activation is crucial for heregulin (HRG)-induced mitogenesis in human breast epithelial cells.
- The precise role of PI3K activation in HRG-mediated growth inhibition remains unclear.
Purpose of the Study:
- To investigate the effects of heregulin beta 1 (HRG) on the growth and PI3K activation in a nonneoplastic human mammary epithelial cell line (184B5).
Main Methods:
- Treatment of 184B5 cells with varying concentrations of HRG.
- Assessment of cell growth via [3H] thymidine incorporation.
- Measurement of erbB3 tyrosine phosphorylation and PI3K association with erbB3.
- Utilizing wortmannin, a PI3K inhibitor, to evaluate pathway involvement.
Main Results:
- Low HRG concentrations stimulated 184B5 cell growth threefold; high concentrations inhibited growth by 50%.
- HRG consistently increased erbB3 tyrosine phosphorylation and PI3K-erbB3 association across all tested concentrations.
- Wortmannin treatment reversed both the stimulatory and inhibitory effects of HRG on DNA synthesis.
Conclusions:
- Both the growth-inhibitory and growth-stimulatory effects of HRG in nonneoplastic human mammary epithelial cells are mediated by phosphatidylinositol 3-kinase (PI-3K) activation.
- This study elucidates a dual role for PI3K signaling in HRG-induced cellular responses within the mammary epithelium.