Related Experiment Videos
Processing and lysosomal localization of a glycoprotein whose secretion is transformation stimulated
The Journal of Cell Biology
|February 1, 1985
Summary
The major excreted protein (MEP) is a mannose 6-phosphate glycoprotein. Transformed cells secrete more MEP, with some forms localized to lysosomes, suggesting MEP is a lysosomal protein secreted by cancer cells.
Area of Science:
- Cell Biology
- Biochemistry
- Cancer Research
Background:
- The major excreted protein (MEP) is a mannose 6-phosphate glycoprotein.
- MEP synthesis and secretion increase in malignantly transformed 3T3 cells.
- Tumor promoters and growth factors also increase MEP synthesis.
Purpose of the Study:
- To investigate the cellular localization and processing of MEP.
- To determine if MEP is secreted by transformed cells.
- To understand the role of MEP in cellular transformation.
Main Methods:
- Pulse-chase labeling and immunoprecipitation of MEP.
- Western blot analysis to quantify MEP forms.
- Subcellular fractionation and immunolocalization (light and electron microscopy).
Main Results:
- Transformed cells secrete 50-60% of synthesized MEP, while non-transformed cells secrete less.
- Cellular MEP levels are fourfold higher in transformed cells.
- MEP and its processed forms (29,000 and 20,000 Da) localize to lysosomes and Golgi in both cell types.
Conclusions:
- MEP is processed into lower molecular weight forms sequestered within the cell.
- MEP exhibits characteristics of a lysosomal protein.
- Transformed cells exhibit increased secretion of MEP, supporting its role in cellular transformation.