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Cell-type specific interaction of Neu differentiation factor (NDF/heregulin) with Neu/HER-2 suggests complex
E Peles1, R Ben-Levy, E Tzahar
1Department of Chemical Immunology, Weizmann Institute of Science, Rehovot, Israel.
Abstract:
The Neu/HER-2 receptor tyrosine kinase is overexpressed in some types of human adenocarcinomas, including tumors of the breast and the ovary. A 44 kDa glycoprotein that elevates tyrosine phosphorylation of Neu has been isolated and named Neu differentiation factor (NDF), or heregulin. Here we show that NDF affects tyrosine phosphorylation of Neu in human tumor cells of breast, colon and neuronal origin, but not in ovarian cells that overexpress the receptor. By using monoclonal antibodies (mAbs) to Neu, we found that the ovarian receptor is immunologically and biochemically similar to the mammary p185neu. Nevertheless, unlike breast-derived Neu, the ovarian protein did not display covalent cross-linking to radiolabeled NDF, and was devoid of ligand-induced association with phosphatidylinositol 3'-kinase. Direct binding analysis showed that NDF binds with high affinity (Kd approximately 10(-9) M) to mammary cells, but its weak association with ovarian cells is probably mediated by heparin-like molecules. Similar to the endogenous receptor, the ectopically overexpressed Neu of mammary cells, but not of ovarian and fibroblastic cells, exhibited elevated levels of NDF-induced phosphorylation and covalent cross-linking of the radiolabeled factor. Taken together, our results imply that NDF binding to cells requires both Neu and an additional cellular component, whose identity is still unknown, but its tissue distribution is more restricted than the expression of the neu gene.
Insights
Neu differentiation factor (NDF) binds breast and colon tumor cells but not ovarian tumor cells, despite similar Neu/HER-2 receptor expression. This suggests NDF requires an additional, tissue-specific cellular component for binding and signaling.
Area of Science:
- Oncology
- Molecular Biology
- Cell Signaling
Background:
- The Neu/HER-2 receptor tyrosine kinase is overexpressed in human adenocarcinomas, including breast and ovarian tumors.
- Neu differentiation factor (NDF), also known as heregulin, is a glycoprotein that elevates Neu tyrosine phosphorylation.
Purpose of the Study:
- To investigate the differential effects of NDF on Neu/HER-2 receptor tyrosine kinase in various human tumor cells.
- To elucidate the mechanisms underlying NDF binding and activation in breast versus ovarian cancer cells.
Main Methods:
- Utilized monoclonal antibodies (mAbs) to analyze Neu receptor characteristics.
- Performed direct binding analysis to assess NDF-cell interactions.
- Investigated ligand-induced association with phosphatidylinositol 3'-kinase (PI3K).
- Examined NDF-induced phosphorylation and covalent cross-linking of Neu.
Main Results:
- NDF induced Neu tyrosine phosphorylation in breast, colon, and neuronal tumor cells, but not in ovarian tumor cells overexpressing Neu.
- Ovarian Neu receptors were immunologically and biochemically similar to mammary Neu but lacked covalent cross-linking to NDF and PI3K association.
- NDF bound with high affinity to mammary cells, while association with ovarian cells was weak and likely mediated by heparin-like molecules.
- Ectopically overexpressed Neu in mammary cells showed NDF-induced phosphorylation and cross-linking, unlike in ovarian and fibroblastic cells.
Conclusions:
- NDF binding to cells requires both the Neu receptor and an additional, unidentified cellular component.
- This additional component exhibits a more restricted tissue distribution than the neu gene itself.
- The findings highlight differential NDF responsiveness in cancer cells, impacting therapeutic strategies.