Lipopolysaccharide activates plasma-membrane signaling and endosomal signaling by Toll-like receptor 4 (TLR4) through the TIRAP-MyD88 and TRAM-TRIF adaptor complexes, respectively, but it is unclear how the signaling switch between these cell compartments is coordinated. In dendritic cells, we found that the p110δ isoform of phosphatidylinositol-3-OH kinase (PI(3)K) induced internalization of TLR4 and dissociation of TIRAP from the plasma membrane, followed by calpain-mediated degradation of TIRAP. Accordingly, inactivation of p110δ prolonged TIRAP-mediated signaling from the plasma membrane, which augmented proinflammatory cytokine production while decreasing TRAM-dependent endosomal signaling that generated antiinflammatory cytokines (interleukin 10 and interferon-β). In line with that altered signaling output, p110δ-deficient mice showed enhanced endotoxin-induced death. Thus, by controlling the 'topology' of TLR4 signaling complexes, p110δ balances overall homeostasis in the TLR4 pathway.

Reepithelialization is a critical step in wound healing. It is initiated by keratinocyte migration at the wound edges. After wounding, extracellular nucleotides are released by keratinocytes and other skin cells. Here, we report that activation of P2Y2 nucleotide receptor by ATP/UTP inhibits keratinocyte cell spreading and induces lamellipodium withdrawal. Kymography analysis demonstrates that these effects correlate with a durable decrease of lamellipodium dynamics. P2Y2 receptor activation also induces a dramatic dismantling of the actin network, the loss of alpha3 integrin expression at the cell periphery, and the dissolution of focal contacts as indicated by the alteration of alpha(v) integrins and focal contact protein distribution. In addition, activation of P2Y2R prevents growth factor-induced phosphorylation of Erk(1,2) and Akt/PkB. The use of a specific pharmacological inhibitor (YM-254890), the depletion of G alpha(q/11) by siRNA, or the expression of a constitutively active G alpha(q/11) mutant (Q209L) show that activation of G alpha(q/11) is responsible for these ATP/UTP-induced effects. Finally, we report that ATP delays growth factor-induced wound healing of keratinocyte monolayers. Collectively, these findings provide evidence for a unique and important role for extracellular nucleotides as efficient autocrine/paracrine regulators of keratinocyte shape and migration during wound healing.

The integrin ␣6␤1 and its main ligand laminin-111 are overexpressed in glioblastoma, as compared with normal brain tissue, suggesting they may be involved in glioblastoma malignancy. To address this question, we stably expressed the ␣6 integrin subunit in the U87 cell line via retroviral-mediated gene transfer. We show that cell surface expression of the ␣6␤1 integrin led to dramatic changes in tumor U87 cell behavior, both in vitro and in vivo. Nude mice receiving either subcutaneous or intracerebral inoculation of ␣6␤1-expressing cells developed substantially more voluminous tumors than mice injected with control cells. The difference in tumor growth was associated with a marked increase in vascularization in response to ␣6␤1 integrin expression and may also be related to changes in the balance between cell proliferation and survival. Indeed, expression of ␣6␤1 enhanced proliferation and decreased apoptosis of U87 cells both in the tumor and in vitro. Additionally, we demonstrate that ␣6␤1 is implicated in glioblastoma cell migration and invasion and that laminin-111 might mediate dissemination of ␣6␤1-positive cells in vivo. Our results highlight for the first time the considerable role of the integrin ␣6␤1 in glioma progression. Malignant brain tumors have an increasing incidence in both children and adults. In adults, the most common type of primary brain tumor, malignant glioma, is considered as one of the deadliest of human cancers. Despite recent advances in both diagnostic modalities and therapeutic strategies, the 5-year survival rate of less than 3% in patients with glioblastoma is among the lowest for all cancers.1 Patients with the most malignant histopathological subtype, glioblastoma, carry the worst prognosis, with median survival rate of less than 1 year, despite aggressive surgery associated with adjuvant radiotherapy and chemotherapy. 1 Glioblastoma are characterized by rapidly dividing cells, high degree of vascularity, invasion into normal brain tissue, and an intense resistance to death-inducing stimuli.2,3 Since integrins, the major family of extracellular matrix (ECM) receptors, are involved in these events, they are one of the most promising molecules to consider for a targeted therapy.Integrins are cell surface transmembrane ␣␤ heterodimers that recognize specific ECM ligands. The combination of ␣ and ␤ subunits, leading to the formation of at least 24 receptors, determines the ligand specificity. 4 Glioblastoma commonly displays enhanced expression of several integrins along with their ECM ligands: ␣v␤3 and ␣v␤5 (tenascin and vitronectin receptors), ␣5␤1 (fibronectin receptor), ␣2␤1 (collagens receptor), and ␣3␤1, ␣6␤4, and ␣6␤1 (laminins receptors).5 Numerous studies have focused on the ␣v integrin family. The integrins ␣v␤3 and ␣v␤5 are markers of glioblastoma malignancy 6 and influence a variety of processes in glioblastoma progression in vivo, including proliferation, apoptosis, and angiogenesis.7 Furthermore, cilengitide, an ␣v␤3 and ␣v␤5 integrins antagonist, extends mouse surviv...