The Saccharomyces cerevisiae gene product SDC25 C-domain functions as an oncoprotein in NIH3T3 cells

Area of Science:

• Cellular biology
• Molecular oncology
• Signal transduction

Background:

• Ras proteins regulate cell signaling by cycling between GTP-bound (active) and GDP-bound (inactive) states.
• Guanine nucleotide exchange factors (GEFs) are essential for Ras activation by facilitating GDP to GTP exchange.
• The yeast CDC25 gene product is a known GEF; its homologue SDC25 has a C-terminus domain with potential GEF activity.

Purpose of the Study:

• To investigate the function of the SDC25 C-terminus domain in mammalian cells.
• To determine if the SDC25 C-terminus domain can activate Ras proteins and induce cellular transformation.
• To explore the implications for Ras signaling in human tumorigenesis.

Main Methods:

• Stable expression of the SDC25 C-terminus domain in NIH3T3 cells.
• Analysis of Ras protein GTP-binding status in transfected cells.
• Coexpression studies with wild-type Ha-Ras to assess effects on tumorigenic properties.

Main Results:

• The SDC25 C-terminus domain promoted GTP binding to Ras p21 in CHO cells.
• Stable expression of the SDC25 C-terminus domain induced NIH3T3 cell transformation.
• Ras proteins in these transformed cells were predominantly GTP-bound.
• Coexpression with Ha-Ras enhanced NIH3T3 cell tumorigenicity.

Conclusions:

• The SDC25 C-terminus domain possesses guanine nucleotide exchange factor activity for Ras in mammalian cells.
• Aberrant activation of mammalian Ras GEFs could contribute to oncogenic Ras signaling in human tumors.
• This study provides a mechanistic link between GEF activity and Ras-driven transformation.