COMMD1 and PtdIns(4,5)P2 interaction maintain ATP7B copper transporter trafficking fidelity in HepG2 cells

Copper-responsive intracellular ATP7B trafficking is critical to maintain copper balance in mammalian hepatocytes and thus organismal copper levels. The COMMD1 protein binds both the ATP7B copper transporter and phosphatidylinositol (4,5)-bisphosphate (PtdIns(4,5)P2), while COMMD1 loss causes hepatocyte copper accumulation. Although it is clear that COMMD1 is included in endocytic trafficking complexes, a direct function for COMMD1 in ATP7B trafficking has not been defined. In this study, experiments using quantitative reveal that COMMD1 modulates the copper-responsive ATP7B trafficking through recruitment to PtdIns(4,5)P2. Decreased COMMD1 abundance results in loss of ATP7B from lysosomes and the trans-Golgi network (TGN) in high copper conditions, while excess expression of COMMD1 also disrupts ATP7B trafficking and TGN structure. Overexpression of COMMD1 mutated to inhibit PtdIns(4,5)P2 binding has little impact on ATP7B trafficking. A mechanistic PtdIns(4,5)P2-mediated function for COMMD1 is proposed that is consistent with decreased cellular copper export due to disruption of the ATP7B trafficking itinerary and accumulation in the early endosome when COMMD1 is depleted. PtdIns(4,5)P2 interaction with COMMD1 as well as COMMD1 abundance may both be important in maintenance of specific membrane protein trafficking pathways.\n\nSUMMARYQuantitative analysis of 3D protein colocalization defines the cellular function of COMMD1 in maintenance of ATP7B copper transporter trafficking fidelity and the importance of PtdIns(4,5)P2 in this action.