Angiogenesis contributes to various pathological conditions. Due to the resistance against existing antiangiogenic therapy, an urgent need exists to understand the molecular basis of vessel growth and to identify new targets for antiangiogenic therapy. Here we show that cyclin-dependent kinase 5 (Cdk5), an important modulator of neuronal processes, regulates endothelial cell migration and angiogenesis, suggesting Cdk5 as a novel target for antiangiogenic therapy. Inhibition or knockdown of Cdk5 reduces endothelial cell motility and blocks angiogenesis in vitro and in vivo. We elucidate a specific signaling of Cdk5 in the endothelium; in contrast to neuronal cells, the motile defects upon inhibition of Cdk5 are not caused by an impaired function of focal adhesions or microtubules but by the reduced formation of lamellipodia. Inhibition or down-regulation of Cdk5 decreases the activity of the small GTPase Rac1 and results in a disorganized actin cytoskeleton. Constitutive active Rac1 compensates for the inhibiting effects of Cdk5 knockdown on migration, suggesting that Cdk5 exerts its effects in endothelial cell migration via Rac1. Our work elucidates Cdk5 as a pivotal new regulator of endothelial cell migration and angiogenesis. It suggests Cdk5 as a novel, pharmacologically accessible target for antiangiogenic therapy and provides the basis for a new therapeutic application of Cdk5 inhibitors as antiangiogenic agents.Angiogenesis is involved in various pathological conditions, including arthritis, psoriasis, diabetic retinopathy, macula degeneration, and cancer (1). During recent years, the search for antiangiogenic compounds and their molecular targets has been intensified. Due to its key role in angiogenesis, research initially focused on vascular endothelial growth factor (VEGF). VEGF receptor inhibitors such as the monoclonal antibody bevacizumab (Avastin) as well as VEGF tyrosine kinase inhibitors such as sunitinib (Sutent) or sorafenib (Nexavar) have been approved for cancer therapy. Unfortunately, the benefits of these therapeutics are at best transitory and mostly followed by a restoration of tumor growth and progression (2). This resistance to antiangiogenic therapy causes a great need for new targets to inhibit vessel growth, interfering with steps in the angiogenic cascade different from the response to a single growth factor.Cyclin-dependent kinase 5 (Cdk5) is a small serine/threonine kinase belonging to the family of Cdks. In contrast to the cell cycle-related Cdks (e.g. Cdks 1, 2, 4, or 6), Cdk5 is not implicated in cell cycle control (3). Instead, it is an important regulator of neuronal development, and it controls various processes in postmitotic neurons (4). Although it is expressed ubiquitously, so far, just a few reports indicate a function of Cdk5 beyond the nervous system. Scarcely anything is known about a potential function of Cdk5 in the vasculature, and its exact functions and signaling mechanisms in the endothelium remain unknown (5-8).Our aim was to close this gap of knowledge. This i...

The abundance of the multimeric vacuolar ATP-dependent proton pump, V-ATPase, on the plasma membrane of tumor cells correlates with the invasiveness of the tumor cell, suggesting the involvement of V-ATPase in tumor metastasis. V-ATPase is hypothesized to create a proton efflux leading to an acidic pericellular microenvironment that promotes the activity of proinvasive proteases. An alternative, not yet explored possibility is that V-ATPase regulates the signaling machinery responsible for tumor cell migration. Here, we show that pharmacologic or genetic reduction of V-ATPase activity significantly reduces migration of invasive tumor cells in vitro. Importantly, the V-ATPase inhibitor archazolid abrogates tumor dissemination in a syngeneic mouse 4T1 breast tumor metastasis model. Pretreatment of cancer cells with archazolid impairs directional motility by preventing spatially restricted, leading edge localization of epidermal growth factor receptor (EGFR) as well as of phosphorylated Akt. Archazolid treatment or silencing of V-ATPase inhibited Rac1 activation, as well as Rac1-dependent dorsal and peripheral ruffles by inhibiting Rab5-mediated endocytotic/exocytotic trafficking of Rac1. The results indicate that archazolid effectively decreases metastatic dissemination of breast tumors by impairing the trafficking and spatially restricted activation of EGFR and Rho-GTPase Rac1, which are pivotal for directed movement of cells. Thus, our data reveals a novel mechanism underlying the role of V-ATPase in tumor dissemination. Cancer Res; 72(22); 5976-87. Ó2012 AACR.

No abstract