To identify factors responsible for the differential localization and activity of PIK3C2Bin the presence or absence of serum mitogens we took a quantitative functional proteomics approach based on stable isotope labeling of amino acids in cell culture (SILAC). Genome-engineered HEK293T cells endogenously expressing eGFP-PI3KC15were cultured in serum-containing or serum-deprived media containing heavy or light amino acids, and subjected to affinity capture using a GFP trap matrix and LC-MS/MS