Beta-arrestins operate an on/off control switch for focal adhesion kinase activity.

Focal adhesion kinase (FAK) regulates key biological processes downstream of G protein-coupled receptors (GPCRs) in normal and cancer cells, but the modes of kinase activation by these receptors remain unclear. We report that after GPCR stimulation, FAK activation is controlled by a sequence of events depending on the scaffolding proteins ß-arrestins and G proteins. Depletion of ß-arrestins results in a marked increase in FAK autophosphorylation and focal adhesion number. We demonstrate that ß-arrestins interact directly with FAK and inhibit its autophosphorylation in resting cells. Both FAK-ß-arrestin interaction and FAK inhibition require the FERM domain of FAK. Following the stimulation of the angiotensin receptor AT1AR and subsequent translocation of the FAK-ß-arrestin complex to the plasma membrane, ß-arrestin interaction with the adaptor AP-2 releases inactive FAK from the inhibitory complex, allowing its activation by receptor-stimulated G proteins and activation of downstream FAK effectors. Release and activation of FAK in response to angiotensin are prevented by an AP-2-binding deficient ß-arrestin and by a specific inhibitor of ß-arrestin/AP-2 interaction; this inhibitor also prevents FAK activation in response to vasopressin. This previously unrecognized mechanism of FAK regulation involving a dual role of ß-arrestins, which inhibit FAK in resting cells while driving its activation at the plasma membrane by GPCR-stimulated G proteins, opens new potential therapeutic perspectives in cancers with up-regulated FAK.

Rendomab B4, a monoclonal antibody that discriminates the human endothelin B receptor of melanoma cells and inhibits their migration.

Metastatic melanoma is an aggressive cancer with a poor prognostic, and the design of new targeted drugs to treat melanoma is a therapeutic challenge. A promising approach is to produce monoclonal antibodies (mAbs) against the endothelin B receptor (ETB), which is known to be overexpressed in melanoma and to contribute to proliferation, migration and vasculogenic mimicry associated with invasiveness of this cancer. We previously described rendomab-B1, a mAb produced by DNA immunization. It is endowed with remarkable characteristics in term of affinity, specificity and antagonist properties against human ETB expressed by the endothelial cells, but, surprisingly, had poor affinity for ETB expressed by melanoma cells. This characteristic strongly suggested the existence of a tumor-specific ETB form. In the study reported here, we identified a new mAb, rendomab-B4, which, in contrast to rendomab-B1, binds ETB expressed on UACC-257, WM-266-4 and SLM8 melanoma cells. Moreover, after binding to UACC-257 cells, rendomab-B4 is internalized and colocalizes with the endosomal protein EEA-1. Interestingly, rendomab-B4, despite its inability to compete with endothelin binding, is able to inhibit phospholipase C pathway and migration induced by endothelin. By contrast, rendomab-B4 fails to decrease ERK1/2 phosphorylation induced by endothelin, suggesting a biased effect on ETB. These particular properties make rendomab-B4 an interesting tool to analyze ETB-structure/function and a promising starting point for the development of new immunological tools in the field of melanoma therapeutics.

Generation and characterization of rendomab-B1, a monoclonal antibody displaying potent and specific antagonism of the human endothelin B receptor.

Endothelin B receptor (ETBR) is a G protein-coupled receptor able to bind equally to the three identified human endothelin peptides. It is expressed primarily on vascular endothelial cells and involved in various physiological processes including vascular tone homeostasis, enteric nervous system development, melanogenesis and angiogenesis. Furthermore, overactivation or overexpression of ETBR have been associated with the development of various diseases such as cardiovascular disorders and cancers. Therefore, ETBR appears to be relevant target for the therapy or diagnosis of highly prevalent human diseases. In this study, we report the in vitro characterization of rendomab-B1, a monoclonal antibody (mAb) obtained by genetic immunization, which selectively recognizes the native form of human ETBR (hETBR). Rendomab-B1 is the first-reported mAb that behaves as a potent antagonist of hETBR. It recognizes an original extracellular conformational epitope on the receptor, distinct from the endothelin-1 (ET-1) binding site. Rendomab-B1 not only blocks ET-1-induced calcium signaling pathway and triggers rapid receptor internalization on recombinant hETBR-expressing cells, but also exerts pharmacological activities on human vascular endothelial cells, reducing both cell viability and ET-1-induced hETBR synthesis. In addition, binding experiments using rendomab-B1 on different melanoma cell lines reveal the structural and functional heterogeneity of hETBR expressed at the surface of these cancer cells, strongly suggesting the existence of tumor-specific receptors. Collectively, our results underscore the value of rendomab-B1 for research, therapeutic and diagnostic applications dealing with hETBR.

Nanog and Oct4 overexpression increases motility and transmigration of melanoma cells.

PURPOSE: Melanoma tumors are highly heterogeneous and can undergo phenotypic modifications depending on their plasticity and the microenvironment, with shifts between proliferative and invasive states. We have shown that melanoma cells, grown as spheroids in a neural crest cell medium, polarize toward an invasive and motile phenotype, in agreement with transcriptomic modulations, including the up-regulation of Nanog and Oct4. Overexpression of these genes was shown to be associated with poor prognosis and metastatic forms of some cancers. We thus investigated implication of Nanog and Oct4, two embryonic transcription factors, in melanoma motility. METHODS: Our team used stable transfection of Nanog or Oct4 in A375 melanoma cell line to investigate motility in a wound healing assay and a transendothelial migration assay. Using semiquantitative RT-PCR, expression of two gene panels involved either in mesenchymal motility or in amoeboid migration was studied. RESULTS: Strongly enhanced capacities of motility and extravasation were observed with cells overexpressing Oct4 and Nanog. The A375 cell line has been described as having a mesenchymal migration type. However, in the Oct4 and Nanog transfectants, several amoeboid migration markers are strongly induced. Accordingly, amoeboid migration inhibitors decrease significantly the transmigration of Oct4- and Nanog-expressing cells through endothelial cells. CONCLUSIONS: We propose here that Nanog and Oct4 pluripotency marker expression in melanoma cells increases the transmigration capacity of these cells through the gain of amoeboid motility, leading to higher invasiveness and aggressiveness.