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Transformation by the v-fms oncogene product: role of glycosylational processing and cell surface expression
Abstract:
The effect of glycosylational-processing inhibitors on the synthesis, cell surface expression, endocytosis, and transforming function of the v-fms oncogene protein (gp140fms) was examined in McDonough feline sarcoma virus-transformed Fischer rat embryo (SM-FRE) cells. Swainsonine (SW), a mannosidase II inhibitor, blocked complete processing, but an abnormal v-fms protein containing hybrid carbohydrate structures was expressed on the cell surface. SW-treated SM-FRE cells retained the transformed phenotype. In contrast, two glucosidase I inhibitors (castanospermine [CA] and N-methyl-1-deoxynojirimycin [MdN]) blocked carbohydrate remodeling at an early stage within the endoplasmic reticulum and prevented cell surface expression of v-fms proteins. CA-treated SM-FRE cells reverted to the normal phenotype. Neither SW, CA, nor MdN affected either endocytosis or the tyrosine kinase activity associated with the v-fms gene product in vitro. These results demonstrate the necessity of carbohydrate processing for cell surface expression of the v-fms gene product and illustrate the unique ability to modulate the transformed state of SM-FRE cells with the glycosylational-processing inhibitors CA and MdN.
Insights
Glycosylation inhibitors impact v-fms protein expression and cell transformation. Mannosidase II inhibitor swainsonine allowed cell surface expression but maintained transformation, while glucosidase I inhibitors castanospermine and N-methyl-1-deoxynojirimycin blocked expression and reversed transformation.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- The v-fms oncogene protein (gp140fms) plays a crucial role in cell transformation.
- Glycosylation is a key post-translational modification affecting protein function and localization.
Purpose of the Study:
- To investigate the impact of glycosylation processing inhibitors on v-fms protein synthesis, cell surface expression, endocytosis, and transforming function.
- To determine if modulating glycosylation can alter the transformed phenotype of cancer cells.
Main Methods:
- Treatment of McDonough feline sarcoma virus-transformed Fischer rat embryo (SM-FRE) cells with glycosylation inhibitors: swainsonine (mannosidase II inhibitor), castanospermine, and N-methyl-1-deoxynojirimycin (glucosidase I inhibitors).
- Analysis of v-fms protein synthesis, cell surface expression, endocytosis, and tyrosine kinase activity.
- Assessment of the transformed cell phenotype.
Main Results:
- Swainsonine treatment resulted in abnormal v-fms protein with hybrid carbohydrates on the cell surface, maintaining the transformed phenotype.
- Castanospermine and N-methyl-1-deoxynojirimycin blocked early carbohydrate remodeling in the endoplasmic reticulum, preventing v-fms cell surface expression and reverting cells to a normal phenotype.
- Inhibitors did not affect v-fms protein endocytosis or in vitro tyrosine kinase activity.
Conclusions:
- Carbohydrate processing is essential for the cell surface expression of the v-fms gene product.
- Specific glycosylation inhibitors, castanospermine and N-methyl-1-deoxynojirimycin, can modulate the transformed state of SM-FRE cells by preventing proper v-fms protein maturation and localization.