Intracellular retention of membrane-anchored v-sis protein abrogates autocrine signal transduction

Area of Science:

• Molecular Biology
• Cell Biology
• Virology

Background:

• Autocrine transformation by v-sis oncogene is mediated by platelet-derived growth factor (PDGF) receptors.
• A key question is whether intracellularly activated PDGF receptors are sufficient for cell transformation or if cell surface receptor-ligand complexes are necessary.

Purpose of the Study:

• To investigate the role of cell surface localization of v-sis protein in cellular transformation.
• To determine if activated PDGF receptors require cell surface complex formation for autocrine signaling.

Main Methods:

• Utilized an adenoviral ER retention signal (E3/19K) to inhibit cell surface transport of a membrane-anchored v-sis fusion protein.
• Assessed cellular transformation by measuring focus formation in NIH 3T3 cells.
• Monitored PDGF receptor downregulation and proteolytic maturation of the v-sis protein.

Main Results:

• ER-retained v-sis protein exhibited significantly diminished ability to transform NIH 3T3 cells compared to non-retained v-sis.
• ER-retained v-sis did not downregulate PDGF receptors, but transformation occurred upon prolonged culture, suggesting selection for surface-localized protein.
• Transport of v-sis beyond the Golgi apparatus correlated with the acquisition of the transformed phenotype.

Conclusions:

• Productive autocrine interactions mediated by v-sis occur in post-ER compartments, likely involving cell surface receptor-ligand complexes.
• Cell surface localization of the v-sis protein is critical for efficient cellular transformation.
• Suramin treatment reversed transformation and upregulated cell surface PDGF receptors, reinforcing the role of surface complexes.