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Cross‐presentation by MHCI is optimally efficient in type 1 dendritic cells (DC) due to their high capacity for antigen processing. However, through specific pathways, other DCs, such as type 2 DCs and inflammatory DCs (iDCs) can also cross‐present antigens. FcγR‐mediated uptake by type 2 DC and iDC subsets mediates antibody‐dependent cross‐presentation and activation of CD8+ T cell responses. Here, an important role for the p84 regulatory subunit of PI3Kγ in mediating efficient cross‐presentation of exogenous antigens in otherwise inefficient cross‐presenting cells, such as type 2 DCs and GM‐CSF‐derived iDCs is identified. FcγR‐mediated cross‐presentation is shown in type 2 and iDCs depend on the enzymatic activity of the p84/p110γ complex of PI3Kγ, which controls the activity of the NADPH oxidase NOX2 and ROS production in murine spleen type 2 DCs and GM‐CSF‐derived iDCs. In contrast, p84/p110γ is largely dispensable for cross‐presentation by type 1 DCs. These findings suggest that PI3Kγ‐targeted therapies, currently considered for oncological practice, may interfere with the ability of type 2 DCs and iDCs to cross‐present antigens contained in immune complexes. [ABSTRACT FROM AUTHOR]

Class IB phosphoinositide 3-kinase [gamma] (PI3K[gamma],) elicits various immunologic and cardiovascular responses; however, the molecular basis for this signal heterogeneity is unclear. PI3K[gamma] consists of a catalytic p110[gamma] and a regulatory p[87.sup.PIKAP] (p87, also p84) or p101 subunit. Hitherto p87 and p101 are generally assumed to exhibit redundant functions in receptor-induced and G protein [beta][gamma] (G[beta][gamma])-mediated PI3K[gamma] regulation. Here we investigated the molecular mechanism for receptor-dependent p87/[gamma] activation. By analyzing GFP-tagged proteins expressed in HEK293 cells, PI3K[gamma]-complemented bone marrow-derived mast cells (BMMCs) from p110[[gamma].sup.-/-] mice, and purified recombinant proteins reconstituted to lipid vesicles, we elucidated a novel pathway of p87-dependent, G protein-coupled receptor (GPCR)-induced PI3K[gamma] activation. Although p101 strongly interacted with G[beta][gamma] thereby mediating PI3K[gamma] membrane recruitment and stimulation, p87 exhibited only a weak interaction, resulting in modest kinase activation and lack of membrane recruitment. Surprisingly, Ras-GTP substituted the missing G[beta][gamma]-dependent membrane recruitment of p87/p110[gamma] by direct interaction with p110[gamma]suggesting the indispensability of Ras for activation of p87/p110[gamma] Consequently, interference with Ras signaling indeed selectively blocked p87/p110[gamma] but not p101/ p110[gamma] kinase activity in HEK293 and BMMC cells, revealing an important crosstalk between monomeric and trimeric G proteins for p87/p110[gamma] activation. Our data display distinct signaling requirements of p87 and p101, conferring signaling specificity to PI3K[gamma] that could open up new possibilities for therapeutic intervention. confocal life cell imaging | G protein | receptor signaling | mast cells www.pnas.org/cgi/doi/10.1073/pnas.0905506106

Phosphoinositide 3-kinases (PI3K) have long been considered promising drug targets for the treatment of inflammatory and autoimmune disorders as well as cancer and cardiovascular diseases. But the lack of specificity, isoform selectivity and poor biopharmaceutical profile of PI3K inhibitors have so far hampered rigorous disease-relevant target validation. Here we describe the identification and development of specific, selective and orally active small-molecule inhibitors of PI3K[gamma] (encoded by Pik3cg). We show that Pik3cg[sup.-/-] mice are largely protected in mouse models of rheumatoid arthritis; this protection correlates with defective neutrophil migration, further validating PI3K[gamma] as a therapeutic target. We also describe that oral treatment with a PI3K[gamma] inhibitor suppresses the progression of joint inflammation and damage in two distinct mouse models of rheumatoid arthritis, reproducing the protective effects shown by Pik3cg[sup.-/-] mice. Our results identify selective PI3K[gamma] inhibitors as potential therapeutic molecules for the treatment of chronic inflammatory disorders such as rheumatoid arthritis., Author(s): Montserrat Camps [1, 5]; Thomas Ruckle [1, 5]; Hong Ji [1, 5]; Vittoria Ardissone [2]; Felix Rintelen [1]; Jeffrey Shaw [1]; Chiara Ferrandi [2]; Christian Chabert [1]; Corine Gillieron [...]

Research has been conducted on the PI3K/PTEN signaling pathways. The study of cardiomycete-specific inactivation of tumor suppressor PTEN leading to cardiac contractility disease has been carried out and the role of PTEN in cardiomyocyte hypertrophy and GPCR signaling and the functions of PI3K/PTEN pathway in heart muscle contractility modulation are discussed.

PI3Ks play a central role in cell signaling and lead to cell proliferation and survival, motility, secretion, and specialized cell responses such as the respiratory burst of granulocytes (1). It […]

Mast cells are the major effector cells in immunoglobulin E (IgE)-mediated allergy. The high affinity IgE receptor Fc ε RI, as well as G protein-coupled receptors (GPCRs) on the mast cell surface signals to phosphoinositide 3-kinase γ (PI3K γ) to initiate degranulation, cytokine release, and chemotaxis. PI3K γ is therefore considered as a target for treatment of allergic disorders. However, leukocyte PI3K γ is key to many functions in innate and adaptive immunity, and attenuation of host defense mechanisms is an expected adverse effect that complicates treatment of chronic illnesses. PI3K γ operates as a p110 γ /p84 or p110 γ /p101 complex, where p110 γ /p84 requires Ras activation. Here we investigated if modulation of Ras-isoprenylation could target PI3K γ activity to attenuate PI3K γ -dependent mast cell responses without impairment of macrophage functions. In murine bone marrow-derived mast cells, GPCR stimulation triggers activation of N-Ras and H-Ras isoforms, which is followed by the phosphorylation of protein kinase B (PKB/Akt) relayed through PI3K γ. Although K-Ras is normally not activated in Ras wild-type cells, it is able to compensate for genetically deleted N- and H-Ras isoforms. Inhibition of Ras isoprenylation with farnesyltransferase inhibitor FTI-277 leads to a significant reduction of mast cell degranulation, cytokine production, and migration. Complementation experiments expressing PI3K γ adaptor proteins p84 or p101 demonstrated a differential sensitivity towards Ras-inhibition depending on PI3K γ complex composition. Mast cell responses are exclusively p84-dependent and were effectively controlled by FTI-277. Similar results were obtained when GTP-Ras was inactivated by overexpression of the GAP-domain of Neurofibromin-1 (NF-1). Unlike mast cells, macrophages express p84 and p101 but are p101-dominated and thus remain functional under treatment with FTI-277. Our work demonstrates that p101 and p84 have distinct physiological roles, and that Ras dependence of PI3K γ signaling differs between cell types. FTI-277 reduces GPCR-activated PI3K γ responses in p84-expressing but not p101-containing bone marrow derived cells. However, prenylation inhibitors have pleiotropic effects beyond Ras and non-tolerable side-effects that disfavor further clinical validation. Statins are, however, clinically well-established drugs that have previously been proposed to block mast cell degranulation by interference with protein prenylation. We show here that Simvastatin inhibits mast cell degranulation, but that this does not occur via Ras-PI3K γ pathway alterations. [ABSTRACT FROM AUTHOR]