G-protein-coupled receptors (GPCRs), the largest family of cell-surface molecules involved in signal transmission, have recently emerged as crucial players in tumour growth and metastasis. Malignant cells often hijack the normal physiological functions of GPCRs to survive, proliferate autonomously, evade the immune system, increase their blood supply, invade their surrounding tissues and disseminate to other organs. This Review will address our current understanding of the many roles of GPCRs and their signalling circuitry in tumour progression and metastasis. We will also discuss how interfering with GPCRs might provide unique opportunities for cancer prevention and treatment.

Platelet activation occurs in response to vessel injury and is important for the arrest of bleeding. Platelet activation during disease states leads to vascular occlusion and ischemic damage. The P2Y 12 receptor, activated by ADP, plays a central role in platelet activation and is the target of P2Y 12 receptor antagonists that have proven therapeutic value.

Activating mutations in GNAQ and GNA11, encoding members of the Gαq family of G protein α subunits, are the driver uveal melanoma oncogenes, while mutations in Gq-linked G proteincoupled receptors (GPCRs) have been identified recently in numerous human malignancies. How Gαq and its coupled receptors transduce mitogenic signals is still unclear, due to the complexity of signaling events perturbed upon Gq activation. Using of a synthetic biology approach and a genome-wide RNAi screen, we found that a highly conserved guanine nucleotide exchange factor, Trio, is essential to activate Rho- and Rac-regulated signaling pathways acting on JNK and p38, thereby transducing proliferative signals from Gαq to the nucleus independently of PLC-β. Indeed, while many biological responses elicited by Gq depend on the transient activation of second messenger system, Gq utilizes a hardwired protein-protein interaction-based signaling circuitry to achieve the sustained stimulation of proliferative pathways, thereby controlling normal and aberrant cell growth.

Several platelet agonists, including thrombin, collagen, and thromboxane A 2 , cause dense granule release independently of thromboxane generation. Because protein kinase C (PKC) isoforms are implicated in platelet secretion, we investigated the role of individual PKC isoforms in platelet dense granule release. PKC␦ was phosphorylated in a time-dependent manner that coincided with dense granule release in response to protease-activated receptor-activating peptides SFLLRN and AYPGKF in human platelets. Only agonists that caused platelet dense granule secretion activated PKC␦. SFLLRN-or AYPGKF-induced dense granule release and PKC␦ phosphorylation occurred at the same respective agonist concentration. Furthermore, AYPGKF and SFLLRN-induced dense granule release was blocked by rottlerin, a PKC␦ selective inhibitor. In contrast, convulxin-induced dense granule secretion was potentiated by rottlerin but was abolished by Go6976, a classical PKC isoform inhibitor. However, SFLLRN-induced dense granule release was unaffected in the presence of Go6976. Finally, rottlerin did not affect SFLLRN-induced platelet aggregation, even in the presence of dimethyl-BAPTA, indicating that PKC␦ has no role in platelet fibrinogen receptor activation. We conclude that PKC␦ and the classical PKC isoforms play a differential role in platelet dense granule release mediated by protease-activated receptors and glycoprotein VI. Furthermore, PKC␦ plays a positive role in protease-activated receptor-mediated dense granule secretion, whereas it functions as a negative regulator downstream of glycoprotein VI signaling.

Despite our improved understanding of cancer, the 5-year survival rate for head and neck squamous cell carcinomas (HNSCC) patients remains relatively unchanged at 50% for the past three decades. HNSCC often metastasize to locoregional lymph nodes, and lymph node involvement represents one of the most important prognostic factors of poor clinical outcome. Among the multiple dysregulated molecular mechanism in HNSCC, emerging basic, preclinical, and clinical findings support the importance of the mTOR signaling route in HNSCC progression. Indeed, we observed here that the activation of mTOR is a widespread event in clinical specimens of HNSCC invading locoregional lymph nodes. We developed an orthotopic model of HNSCC consisting in the implantation of HNSCC cells into the tongues of immunocompromised mice. These orthotopic tumors spontaneously metastasize to the cervical lymph nodes, where the presence of HNSCC cells can be revealed by histological and immunohistochemical evaluation. Both primary and metastatic experimental HNSCC lesions exhibited elevated mTOR activity. The ability to monitor and quantitate lymph node invasion in this model system enabled us to explore whether the blockade of mTOR could impact on HNSCC metastasis. We found that inhibition of mTOR with rapamycin and the rapalog RAD001 diminished lymphangiogenesis in the primary tumors and prevented the dissemination of HNSCC cancer cells to the cervical lymph nodes, thereby prolonging animal survival. These findings may provide a rationale for the future clinical evaluation of mTOR inhibitors, including rapamycin and its analogs, as part of a molecular-targeted metastasis preventive strategy for the treatment of HNSCC patients.

Platelet activation occurs in response to vessel injury and is important for the arrest of bleeding. Platelet activation during disease states leads to vascular occlusion and ischemic damage. The P2Y 12 receptor, activated by ADP, plays a central role in platelet activation and is the target of P2Y 12 receptor antagonists that have proven therapeutic value.

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Activation of GPIIb/IIIa is known to require agonistinduced inside-out signaling through G q , G i , and G z . Although activated by several platelet agonists, including thrombin and thromboxane A 2 , the contribution of the G 12/13 signaling pathway to GPIIb/IIIa activation has not been investigated. In this study, we used selective stimulation of G protein pathways to investigate the contribution of G 12/13 activation to platelet fibrinogen receptor activation. YFLLRNP is a PAR-1-specific partial agonist that, at low concentrations (60 M), selectively activates the G 12/13 signaling cascade resulting in platelet shape change without stimulating the G q or G i signaling pathways. YFLLRNP-mediated shape change was completely inhibited by the p160 ROCK inhibitor, Y-27632. At this low concentration, YFLLRNP-mediated G 12/13 signaling caused platelet aggregation and enhanced PAC-1 binding when combined with selective G i or G z signaling, via selective stimulation of the P2Y 12 receptor or ␣ 2A -adrenergic receptor, respectively. Similar data were obtained when using low dose U46619 (10 nM), a thromboxane A 2