Absolute Quantification of Endogenous Ras Isoform Abundance

Area of Science:

• Molecular Biology
• Cellular Signaling
• Proteomics

Background:

• Ras proteins are key regulators of cell proliferation, differentiation, and survival.
• Three highly similar isoforms (HRAS, KRAS, NRAS) exist with distinct biological and oncogenic roles.

Purpose of the Study:

• To optimize a quantitative proteomics method for precise measurement of Ras isoform protein copy number per cell.
• To understand the relative biological contributions of each Ras isoform.

Main Methods:

• Utilized isotopic protein standards and selected reaction monitoring (SRM) for diagnostic peptides.
• Applied the method to sub-milligram quantities of cell lysates.
• Analyzed Ras isoform abundance in isogenic SW48 colorectal cancer cells.

Main Results:

• Endogenous Ras proteins are highly abundant (≥260,000 copies/cell) in SW48 cells.
• The rank order of isoform abundance is KRAS > NRAS ≥ HRAS.
• Oncogenic KRAS mutants showed increased total Ras abundance and altered mutant/wild-type ratios.

Conclusions:

• The developed proteomics method is sensitive, robust, and suitable for quantifying Ras isoforms.
• Ras protein copy number is crucial for modeling signaling networks and interpreting functional data.
• Findings provide essential quantitative data for understanding Ras isoform-specific functions in cancer.