LPIN1 and breast cancer: Consistent with the proteomic data showing that lipin-1 is the major PAP in human breast cancer samples25, knockdown of LPIN1, but not its homologues LPIN2 or LPIN3, virtually abolished the PAP activity in breast cancer cell lines (Supplementary Fig. 6e, f), confirming that lipin-1 accounts for the majority of PAP activity in these cells.