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Translational suppression of syndecan-1 expression in Ha-ras transformed mouse mammary epithelial cells
J Kirjavainen1, S Leppä, N E Hynes
1Department of Medical Biochemistry, University of Turku, Finland.
Abstract:
A cell surface proteoglycan, syndecan-1, has been shown to participate in the maintenance of the epithelial cell morphology. A point mutated activated c-Ha-ras gene under the control of the glucocorticoid inducible MMTV-LTR promoter was transfected into the mouse mammary epithelial cell line, NOG-8. The NOG-8 ras cells were used to study changes in syndecan-1 expression during epithelial transformation. NOG-8 ras cells, when induced to express Ha-ras, transformed and formed foci in monolayer cultures and colonies in suspension cultures. Expression of syndecan-1 at the cell surface was markedly reduced in cells showing the transformed phenotype. The accumulation of newly synthesized core protein of syndecan-1 was suppressed in these cells, whereas mRNA levels remained unchanged. This novel finding indicates that syndecan-1 expression is translationally suppressed in the Ha-ras-transformed epithelial cells. Hence, syndecan-1 loss during epithelial transformation could take place without altering syndecan gene transcription and, on the other hand, could be one of the critical events involved in malignant transformation.
Insights
Syndecan-1 cell surface expression decreases during epithelial transformation. This loss occurs at the translational level, not affecting gene transcription, and may be key in malignant transformation.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Syndecan-1 is a cell surface proteoglycan crucial for epithelial cell morphology.
- Epithelial transformation involves changes in cell structure and behavior, often linked to cancer development.
Purpose of the Study:
- To investigate the changes in syndecan-1 expression during oncogenic Ha-ras-induced epithelial transformation.
- To determine the regulatory mechanisms controlling syndecan-1 expression in transformed cells.
Main Methods:
- Transfection of a mouse mammary epithelial cell line (NOG-8) with an activated c-Ha-ras gene.
- Induction of Ha-ras expression using a glucocorticoid-inducible promoter.
- Analysis of syndecan-1 cell surface expression and newly synthesized core protein levels.
- Assessment of syndecan-1 mRNA levels.
Main Results:
- Ha-ras expression induced epithelial transformation, characterized by focus formation and colony growth.
- Cell surface syndecan-1 expression was significantly reduced in transformed NOG-8 ras cells.
- Suppression of syndecan-1 core protein accumulation was observed, despite unchanged mRNA levels.
Conclusions:
- Syndecan-1 expression is translationally suppressed in Ha-ras-transformed epithelial cells.
- Loss of syndecan-1 during epithelial transformation can occur independently of changes in gene transcription.
- Downregulation of syndecan-1 may represent a critical event in malignant transformation.