Src homology 2 domain-containing inositol-5-phosphatase 1 (SHIP1) negatively regulates TLR4-mediated LPS response primarily through a phosphatase activity- and PI-3K-independent mechanism

Abstract

Src homology 2 (SH2) domain-containing inositol-5-phosphatase 1 (SHIP1) plays important roles in negatively regulating the activation of immune cells primarily via the phosphoinositide 3-kinase (PI-3K) pathway by catalyzing the PI-3K product PtdIns-3,4,5P3 (phosphatidylinositol-3,4,5-triphosphate) into PtdIns-3,4P2. However, the role of SHIP1 in Toll-like receptor 4 (TLR4)-mediated lipopolysaccharide (LPS) response remains unclear. Here we demonstrate that SHIP1 negatively regulates LPS-induced inflammatory response via both phosphatase activity-dependent and -independent mechanisms in macrophages. SHIP1 becomes tyrosine phosphorylated and up-regulated upon LPS stimulation in RAW264.7 macrophages. SHIP1-specific RNA-interfering and SHIP1 overexpression experiments demonstrate that SHIP1 inhibits LPS-induced tumor necrosis factor α (TNF-α) and interleukin 6 (IL-6) production by negatively regulating the LPS-induced combination between TLR4 and myeloid differentiation factor 88 (MyD88); activation of Ras (p21ras protein), PI-3K, extracellular signal-regulated kinase 1/2 (ERK1/2), p38, and c-Jun NH2-terminal kinase (JNK); and degradation of IκB-α. SHIP1 also significantly inhibits LPS-induced mitogen-activated protein kinase (MAPK) activation in TLR4-reconstitited COS7 cells. Although SHIP1-mediated inhibition of PI-3K is dependent on its phosphatase activity, phosphatase activity-disrupted mutant SHIP1 remains inhibitory to LPS-induced TNF-α production. Neither disrupting phosphatase activity nor using the PI-3K pathway inhibitor LY294002 or wortmannin could significantly block SHIP1-mediated inhibition of LPS-induced ERK1/2, p38, and JNK activation and TNF-α production, demonstrating that SHIP1 inhibits LPS-induced activation of MAPKs and cytokine production primarily by a phosphatase activity- and PI-3K-independent mechanism. (Blood. 2005;105:4685-4692)

IL-10 Inhibits miR-155 Induction by Toll-like Receptors

“…TLR signaling can promote the pro-inflammatory response through the activation of PI3K, resulting in generation of PIP3 and activation of MAPK and NF-B (20). The induction of miR-155 by LPS supports this model, whereby expression of miR-155 can target SHIP1, decreasing its expression and promoting the conversion of PIP2 to PIP3 by PI3K.…”

“…This inhibition of miR-155 by IL-10 led to an increase in the expression of the miR-155 target, SHIP1. Because SHIP1 has been shown to limit TLR signaling (20), the ability of IL-10 to increase its expression via inhibition of miR-155 provides new insights into the complex signaling mechanism of IL-10. This finding also identifies a novel mechanism of control on miR-155, an miRNA that has been implicated in the innate immune response and cancer progression.…”

MicroRNAs in the regulation of TLR and RIG-I pathways

“…4,5 Moreover, any dysregulation of this process has been associated with inflammatory diseases, autoimmune diseases or pathogen dissemination. Many molecules have been identified as positive or negative regulators of TLR signaling, 6,7 including phosphatases (SHP-1, SHP-2, SHIP-1, PTP1B, [8][9][10][11] etc. ), protein kinases (calmodulin-dependent protein kinase II, Btk, MEKK3, [12][13][14] etc.…”

Toll-like receptors, signaling adapters and regulation of the pro-inflammatory response by PI3K

“…Indeed, the ability of SHIP1 to suppress inflammation was found to be independent of its phosphatase activity. 73 Further work remains to fully understand the role SHIP1 plays in TLR signaling in a manner dependent and independent of its role in suppressing PI3K activity.…”