PPP6C and cancer: To investigate C-terminal methylation of endogenous PP2Acα/β, PP4c, PP6c subunits, we enriched PPPs from the human cancer cell lines SW1088, C32, U-87, MCF-7, CAL-51 using PIBs, digested the isolated proteins into peptides, and analyzed them by liquid-chromatography coupled with tandem mass spectrometry (LC–MS/MS) (Fig. 1B).