Small-Molecule Protein-Protein Interaction Inhibitor of Oncogenic Rho Signaling

Uncontrolled activation of Rho signaling by RhoGEFs, in particular AKAP13 (Lbc) and its close homologs, is implicated in a number of human tumors with poor prognosis and resistance to therapy. Structure predictions and alanine scanning mutagenesis of Lbc identified a circumscribed hot region for RhoA recognition and activation. Virtual screening targeting that region led to the discovery of an inhibitor of Lbc-RhoA interaction inside cells. By interacting with the DH domain, the compound inhibits the catalytic activity of Lbc, halts cellular responses to activation of oncogenic Lbc pathways, and reverses a number of prostate cancer cell phenotypes such as proliferation, migration, and invasiveness. This study provides insights into the structural determinants of Lbc-RhoA recognition. This is a successful example of structure-based discovery of a small protein-protein interaction inhibitor able to halt oncogenic Rho signaling in cancer cells with therapeutic implications

Rôle of AKAP2 in prostate cancer developinent

Prostate Cancer (PC) is the most common type of cancer in men in the western countries. The growth and development of primary prostate cancer cells rely on circulating androgens and on androgen receptors (AR), thus generally the standard therapy for the treatment of localized and advanced PC is the androgen deprivation therapy in the form of médical or surgical castration. Eventually however, the disease progresses to castration-résistant prostate cancer (CRPC), an aggressive and lethal form capable of growing in presence of low levels of androgens. It has become increasingly clear that the coordination of the signaling events leading to cancer formation and progression is under the control of macromolecular transduction complexes organized by scaffolding proteins. A-kinase anchoring proteins (AKAPs) constitute a family of scaffold proteins that coordinate the spatio-temporal activation of PKA and other signaling enzymes involved in the modulation of pathways controlling, among others, cancer cell prolifération, cell survival and invasion. In this context, our results suggest that RNAi-mediated silencing of AKAP2 in DU145 and PC-3 cells leads to a significant réduction in their ability to migrate and to invade. It is well established that PC cell migration is driven by the continuous reorganization and turnover of the actin cytoskeleton which drives the formation of protrusion named lamellipodia and filopodia. The turnover of these structures is tightly controlled by cofilin, an actin-binding protein crucially involved in actin severing and turnover. Inactivation of cofilin through phosphorylation, inhibits actin filament dynamics, hence migration. In this context, we can show that silencing of AKAP2, increases cofilin phosphorylation, which negatively impacts on DU 145 and PC-3 cell migration. Régulation of cofilin activation via dephosphorylation is mediated by différent phosphatases among which protein phosphatase 1 (PP1). In this regard, we demonstrated that AKAP2 interacts with protein phosphatase 1 catalytic subunit (3 (PPP1CB) in DU145 and PC-3 cells. Our current hypothesis is that AKAP2 regulates PCa cell migration and invasion by enhancing cofilin activity through the scaffolding of PP1. -- Le cancer de la prostate est le type de cancer le plus commun chez les hommes des pays occidentaux. La croissance et le développement du cancer primaire de la prostate dépend d'hormones androgènes et de leurs récepteurs. Ainsi, la thérapie standard pour le traitement du cancer de la prostate localisé ou avancé est le traitement anti-androgénique sous forme de castration médicale ou chirurgicale. Cependant, le cancer peut parfois progressivement évoluer et devenir hormono-résistant, un type de cancer de la prostate très agressif et capable de s'étendre malgré de faibles taux d'androgènes. De plus en plus d'études montrent que la coordination de différentes voies de signalisation impliquées dans la formation du cancer est sous le contrôle de complexes de transduction macromoléculaires, organisés par des protéines d'ancrage. Les A-kinase anchoring proteins (AKAPs) sont des protéines d'ancrage qui coordonnent l'activation spatio-temporel de la PKA ainsi que d'autres enzymes impliquées dans la modulation de voies de signalisation contrôlant, entre autres, la prolifération et l'invasion des cellules tumorales. Dans ce contexte, nos résultats suggèrent que la suppression d'AKAP2 induite par des siRNA dans les cellules DU145 et PC-3 entraîne une réduction significative de leur capacité à migrer et à envahir. Il est bien établi que la migration des cellules tumorales est régulée par la réorganisation et le turnover continu du cytosquelette d'actine, qui entraînent la formation d'extensions membranaires appelées lamellipodes et filopodes. Le turnover de ces structures est strictement contrôlé par la cofiline, une protéine de liaison à l'actine qui joue un rôle crucial dans la dépolymérisation de l'actine. L'inactivation de la cofiline par phosphorylation inhibe la dynamique des filaments d'actine, et donc la migration des cellules. Dans ce contexte, nous avons pu montrer que la suppression de l'expression d'AKAP2 augmente la phosphorylation de la cofiline, ce qui a un impact négatif sur la migration des cellules DU145 et PC-3. La régulation de l'activation de la cofiline via sa déphosphorylation est induite par différentes phosphatases, parmi lesquelles la protéine phosphatase 1 (PP1). Ainsi, nous avons démontré qu'AKAP2 interagit avec la sous-unité catalytique de la protéine phosphatase 1 beta (PPP1CB) dans les cellules DU145 et PC-3. Notre hypothèse actuelle est qu'AKAP2 régule la migration et l'invasion des cellules du cancer de la prostate en augmentant l'activité de la cofiline, par le biais de l'ancrage de PP1

Emerging roles of A-kinase anchoring proteins in cardiovascular pathophysiology

Heart and blood vessels ensure adequate perfusion of peripheral organs with blood and nutrients. Alteration of the homeostatic functions of the cardiovascular system can cause hypertension, atherosclerosis, and coronary artery disease leading to heart injury and failure. A-kinase anchoring proteins (AKAPs) constitute a family of scaffolding proteins that are crucially involved in modulating the function of the cardiovascular system both under physiological and pathological conditions. AKAPs assemble multifunctional signaling complexes that ensure correct targeting of the cAMP-dependent protein kinase (PKA) as well as other signaling enzymes to precise subcellular compartments. This allows local regulation of specific effector proteins that control the function of vascular and cardiac cells. This review will focus on recent advances illustrating the role of AKAPs in cardiovascular pathophysiology. The accent will be mainly placed on the molecular events linked to the control of vascular integrity and blood pressure as well as on the cardiac remodeling process associated with heart failure. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel

AKAP2-anchored protein phosphatase 1 controls prostatic neuroendocrine carcinoma cell migration and invasion

Prostate cancer (PC) is the second leading cause of cancer-related death in men. The growth of primary prostate cancer cells relies on circulating androgens and thus the standard therapy for the treatment of localized and advanced PC is the androgen deprivation therapy. Prostatic neuroendocrine carcinoma (PNEC) is an aggressive and highly metastatic subtype of prostate cancer, which displays poor prognosis and high lethality. Most of PNECs develop from prostate adenocarcinoma in response to androgen deprivation therapy, however the mechanisms involved in this transition and in the elevated biological aggressiveness of PNECs are poorly defined. Our current findings indicate that AKAP2 expression is dramatically upregulated in PNECs as compared to non-cancerous prostate tissues. Using a PNEC cell model, we could show that AKAP2 is localized both intracellularly and at the cell periphery where it colocalizes with F-actin. AKAP2 and F-actin interact directly through a newly identified actin-binding domain located on AKAP2. RNAi-mediated silencing of AKAP2 promotes the phosphorylation and deactivation of cofilin, a protein involved in actin turnover. This effect correlates with a significant reduction in cell migration and invasion. Co-immunoprecipitation experiments and proximity ligation assays revealed that AKAP2 forms a complex with the catalytic subunit of protein phosphatase 1 (PP1) in PNECs. Importantly, AKAP2-mediated anchoring of PP1 to the actin cytoskeleton regulates cofilin dephosphorylation and activation, which, in turn, enhances F-actin dynamics and favors migration and invasion. In conclusion, this study identified AKAP2 as an anchoring protein overexpressed in PNECs that controls cancer cell invasive properties by regulating cofilin phosphorylation