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Selective secretion of alternatively spliced fibronectin variants
J E Schwarzbauer1, C S Spencer, C L Wilson
1Department of Biology, Princeton University, New Jersey 08544.
The Journal of Cell Biology
|December 1, 1989
Summary
The variable (V) region of fibronectin (FN) is essential for secreting FN dimers. Specific segments within the V region, like V120 and V95, enable dimer secretion, while V0 prevents it, highlighting the V region's role in FN dimer formation and release.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Fibronectin (FN) is a crucial extracellular matrix protein involved in cell adhesion and migration.
- FN exists as disulfide-bonded dimers, but the molecular mechanisms governing their secretion are not fully understood.
- Alternative splicing of the FN transcript generates variants with differing functional properties.
Purpose of the Study:
- To investigate the role of the alternatively spliced variable (V) region of fibronectin in the secretion of FN dimers.
- To identify specific segments within the V region that regulate dimer secretion.
- To understand the implications of V region variants on FN dimer assembly and cellular processing.
Main Methods:
- Expression of variant fibronectin cDNAs (V120, V95, V0) in normal and transformed fibroblasts.
- Biosynthetic analyses using pulse-chase and time course experiments to study dimer formation and secretion.
- Deletion mapping to pinpoint critical sequences within the V region involved in secretion.
- Analysis of plasma fibronectin composition.
Main Results:
- Fibronectin polypeptides (deminectins) containing the V120 or V95 segments are efficiently secreted as homodimers.
- Homodimers of V0 deminectins, lacking the V region, are poorly secreted and likely degraded intracellularly.
- Coexpression studies show that only dimers containing V120 subunits are secreted, indicating selective retention of V0-containing dimers.
- An 18-amino acid segment within V95 is critical for deminectin dimer secretion.
- Plasma fibronectin lacks V0-V0 dimers, consistent with findings in cell culture.
Conclusions:
- The variable (V) region of fibronectin is indispensable for the efficient secretion of FN dimers.
- Specific segments within the V region, particularly an 18-amino acid sequence in V95, are required for proper dimer secretion.
- The V region likely mediates intracellular protein-protein interactions necessary for the formation and release of native FN dimers.