Membrane contact site resident PTP1B limits superoxide production by suppressing a Syk-Shc1-Phagocyte Oxidase relay.

Abstract

Phagocytosis is a specialized endocytic process used by macrophages and dendritic cells to engulf particles, which requires coordinated signaling cascades, cytoskeletal remodeling, and assembly of antimicrobial machinery to eliminate pathogens. During Fc {gamma} receptor (Fc{gamma}R)-mediated phagocytosis, dynamic actin depolymerization at the base of the phagocytic cup creates permissive conditions for endoplasmic reticulum-plasma membrane (ER-PM) membrane contact sites (MCS) to form. We demonstrate that the ER-resident protein tyrosine phosphatase PTP1B localizes to newly formed or expanded ER-PM MCS during phagocytosis and dephosphorylates Syk. Using TIRF microscopy with MCS residents, including MAPPER, STIM1, and E-Syts, we show that actin clearance allows ER proteins to approach the plasma membrane. PTP1B colocalizes with Fc{gamma}Rs in actin-cleared zones and physically interacts with Syk, a critical mediator of phagocytic signaling. Loss of PTP1B led to sustained Syk hyperphosphorylation without affecting phagocytosis. However, the PTP1B-deficient cells showed a {asymp}3-fold increase in NADPH oxidase 2 (NOX2)-mediated superoxide production. Using unbiased proteomics, we identified the adapter protein Shc1 as a critical intermediate linking Syk phosphorylation to NOX2 activation. Shc1 phosphorylation during phagocytosis is dependent on Src family kinases and Syk, while genetic ablation of SHC1 reduced superoxide production by {asymp}40%. Proximity ligation assays reveal enhanced Shc1-p47phox interactions in PTP1B-deficient cells during phagocytosis. These findings establish an SFK-Syk-Shc1-NOX2 signaling axis that PTP1B negatively regulates at MCS between the ER and the forming phagosome, providing new mechanistic insights into antimicrobial responses during phagocytosis.