The G protein-coupled, receptor-activated phosphoinositide 3-kinase gamma (PI3Kgamma) mediates inflammatory responses and negatively controls cardiac contractility by reducing cAMP concentration. Here, we report that mice carrying a targeted mutation in the PI3Kgamma gene causing loss of kinase activity (PI3KgammaKD/KD) display reduced inflammatory reactions but no alterations in cardiac contractility. We show that, in PI3KgammaKD/KD hearts, cAMP levels are normal and that PI3Kgamma-deficient mice but not PI3KgammaKD/KD mice develop dramatic myocardial damage after chronic pressure overload induced by transverse aortic constriction (TAC). Finally, our data indicate that PI3Kgamma is an essential component of a complex controlling PDE3B phosphodiesterase-mediated cAMP destruction. Thus, cardiac PI3Kgamma participates in two distinct signaling pathways: a kinase-dependent activity that controls PKB/Akt as well as MAPK phosphorylation and contributes to TAC-induced cardiac remodeling, and a kinase-independent activity that relies on protein interactions to regulate PDE3B activity and negatively modulates cardiac contractility.

Hypertension affects nearly 20% of the population in Western countries and strongly increases the risk for cardiovascular diseases. In the pathogenesis of hypertension, the vasoactive peptide of the renin-angiotensin system, angiotensin II and its G protein–coupled receptors (GPCRs), play a crucial role by eliciting reactive oxygen species (ROS) and mediating vessel contractility. Here we show that mice lacking the GPCR-activated phosphoinositide 3-kinase (PI3K)γ are protected from hypertension that is induced by administration of angiotensin II in vivo. PI3Kγ was found to play a role in angiotensin II–evoked smooth muscle contraction in two crucial, distinct signaling pathways. In response to angiotensin II, PI3Kγ was required for the activation of Rac and the subsequent triggering of ROS production. Conversely, PI3Kγ was necessary to activate protein kinase B/Akt, which, in turn, enhanced L-type Ca2+ channel–mediated extracellular Ca2+ entry. These data indicate that PI3Kγ is a key transducer of the intracellular signals that are evoked by angiotensin II and suggest that blocking PI3Kγ function might be exploited to improve therapeutic intervention on hypertension.

Gene‐targeted mice were used to evaluate the role of the gamma isoform of phosphoinositide 3‐kinase (PI3Kγ) in dendritic cell (DC) migration and induction of specific T‐cell‐mediated immune responses. DC obtained from PI3Kγ−/− mice showed a reduced ability to respond to chemokines in vitro and ex vivo and to travel to draining lymph nodes under inflammatory conditions. PI3Kγ−/− mice had a selective defect in the number of skin Langerhans cells and in lymph node CD8α− DC. Furthermore, PI3Kγ−/− mice showed a defective capacity to mount contact hypersensitivity and delayed‐type hypersensitivity reactions. This defect was directly related to the reduced ability of antigen‐loaded DC to migrate from the periphery to draining lymph nodes. Thus, PI3Kγ plays a nonredundant role in DC trafficking and in the activation of specific immunity. Therefore, PI3Kγ may be considered a new target to control exaggerated immune reactions.

It has been proposed that integrins activate ERK

The small GTP-binding protein Rap1B is activated in human platelets upon stimulation of a G i -dependent signaling pathway. In this work, we found that inhibition of platelet adenylyl cyclase by dideoxyadenosine or SQ22536 did not cause activation of Rap1B and did not restore Rap1B activation in platelets stimulated by cross-linking of Fc␥ receptor IIA (Fc␥RIIA) in the presence of ADP scavengers. Moreover, elevation of the intracellular cAMP concentration did not impair the G idependent activation of Rap1B. Two unrelated inhibitors of phosphatidylinositol 3-kinase (PI3K), wortmannin and LY294002, totally prevented Rap1B activation in platelets stimulated by cross-linking of Fc␥RIIA, by stimulation of the P2Y 12 receptor for ADP, or by epinephrine. However, in platelets from PI3K␥-deficient mice, both ADP and epinephrine were still able to normally stimulate Rap1B activation through a PI3K-dependent mechanism, suggesting the involvement of a different isoform of the enzyme. Moreover, the lack of PI3K␥ did not prevent the ability of epinephrine to potentiate platelet aggregation through a G i -dependent pathway. The inhibitory effect of wortmannin on Rap1B activation was overcome by addition of phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P 3 ), but not PtdIns(3,4)P 2 , although both lipids were found to support phosphorylation of Akt. Moreover, PtdIns(3,4,5)P 3 was able to relieve the inhibitory effect of apyrase on Fc␥RIIA-mediated platelet aggregation. We conclude that stimulation of a G i -dependent signaling pathway causes activation of the small GTPase Rap1B through the action of the PI3K product PtdIns(3,4,5)P 3 , but not PtdIns(3,4)P 2 , and that this process may contribute to potentiation of platelet aggregation.Rap1B is a small GTP-binding protein highly expressed in human platelets (1). In resting cells, it is mainly located at the membrane, but it translocates to the cytosol upon phosphorylation by protein kinase A (2). In activated platelets, Rap1B rapidly interacts with the reorganized actin-based cytoskeleton (3). As other GTPases, Rap1B is activated by binding of GTP. Platelet stimulation by different agonists, such as thrombin, collagen, and ADP, induces the rapid binding of GTP to Rap1B (4, 5). An increase in the intracellular Ca 2ϩ concentration in stimulated platelets has been shown to be sufficient to promote Rap1B activation, and specific Ca 2ϩ /calmodulin-sensitive guanine nucleotide exchange factors for Rap1B have been identified (5, 6). We (7) and others (8) have recently described a new pathway for Rap1B activation that is initiated by stimulation of membrane G i -coupled receptors and that is independent of intracellular Ca 2ϩ increases. In fact, the sole binding of ADP to the P2Y 12 receptor, as well as the interaction of epinephrine with the ␣ 2A -adrenergic receptor, is sufficient to trigger Rap1B activation. Moreover, we have found that agonists that activate platelets through stimulation of G q -coupled receptors, such as the thromboxane A 2 analog U46619, or through stimu...