PHLPP Signaling in Immune Cells.

Pleckstrin homology domain leucine-rich repeat protein phosphatases (PHLPP) belong to the protein phosphatase magnesium/manganese-dependent family of Ser/Thr phosphatases. Their general role as tumor suppressors has been documented for over a decade. In recent years, accumulating evidence suggests that PHLPP isozymes have key regulatory roles in both innate and adaptive immunity. In macrophages, PHLPP1 dampens signaling through TLR4 and the IFN-γ receptor by altering cytosolic signaling pathways. Additionally, nuclear-localized PHLPP1 inhibits STAT1-mediated inflammatory gene expression by direct dephosphorylation at Ser 727. PHLPP1 also regulates the migratory and inflammatory capacity of neutrophils in vivo. Furthermore, PHLPP1-mediated dephosphorylation of AKT on Ser 473 is required for both the suppressive function of regulatory T cells and for the pro-apoptotic effects of PHLPP1 in B cell chronic lymphocytic leukemia. In the context of immune homeostasis, PHLPP1 expression is modulated in multiple cell types by inflammatory signals, and the dynamics of its expression have varying effects on the pathogenesis of inflammatory bowel disease and septic shock. In this review, we summarize recent findings on the functions of PHLPP in inflammatory and regulatory signaling in the context of both innate and adaptive immunity.