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The v-sis/PDGF-2 transforming gene product localizes to cell membranes but is not a secretory protein
Abstract:
The v-sis transforming gene encodes the woolly monkey homologue of human platelet-derived growth factor (PDGF) polypeptide 2. After its synthesis on membrane bound polyribosomes, the glycosylated precursor dimerizes in the endoplasmic reticulum and travels through the Golgi apparatus. At the cell periphery, the precursor is processed to yield a dimer structurally analogous to biologically active PDGF. Small amounts of two incompletely processed forms are detectable in tissue culture fluids of simian sarcoma virus (SSV) transformants. However, the vast majority remains cell associated. Thus, this growth factor-related transforming gene product is not a classical secretory protein. These findings define possible cellular locations where the transforming activity of the sis-PDGF-2 protein may be exerted.
Insights
The v-sis gene product, similar to human platelet-derived growth factor (PDGF), is processed at the cell periphery. Most of this growth factor remains cell-associated, not secreted, suggesting localized transforming activity.
Area of Science:
- Molecular Biology
- Cell Biology
- Virology
Background:
- The v-sis transforming gene is a homologue of human platelet-derived growth factor (PDGF) polypeptide 2.
- Understanding the processing and localization of v-sis gene products is crucial for comprehending viral transformation.
Purpose of the Study:
- To investigate the synthesis, dimerization, processing, and cellular localization of the v-sis gene product.
- To determine if the v-sis gene product functions as a classical secretory protein.
Main Methods:
- Analysis of protein synthesis on membrane-bound polyribosomes.
- Tracking glycosylated precursor through the endoplasmic reticulum and Golgi apparatus.
- Detection of processed forms in tissue culture fluids and cell association.
Main Results:
- The v-sis precursor dimerizes in the endoplasmic reticulum and is processed at the cell periphery into a PDGF-analogous dimer.
- Small amounts of incompletely processed forms are found in culture fluids of simian sarcoma virus (SSV) transformants.
- The majority of the sis-PDGF-2 protein remains cell-associated, indicating it is not a classical secretory protein.
Conclusions:
- The sis-PDGF-2 protein is not secreted like typical growth factors.
- The transforming activity of sis-PDGF-2 may be exerted at specific cellular locations.
- These findings provide insights into the mechanism of SSV-induced cell transformation.