Abl kinases are required for vascular function, Tie2 expression, and angiopoietin-1-mediated survival.

Endothelial dysfunction is associated with diverse cardiovascular pathologies. Here, we show a previously unappreciated role for the Abelson (Abl) family kinases (Abl and Arg) in endothelial function and the regulation of angiogenic factor pathways important for vascular homeostasis. Endothelial Abl deletion in Arg-null mice led to late-stage embryonic and perinatal lethality, with mutant mice displaying focal loss of vasculature and tissue necrosis. Loss of Abl kinases led to increased endothelial cell apoptosis both in vitro and in vivo, contributing to vascular dysfunction, infarction, and tissue damage. Mechanistically, we identify a unique dual role for Abl kinases in the regulation of angiopoietin/Tie2 protein kinase signaling. Endothelial Abl kinases modulate Tie2 expression and angiopoietin-1-mediated endothelial cell survival. These findings reveal a critical requirement for the Abl kinases in vascular development and function, which may have important implications for the clinical use of Abl kinase inhibitors.

Role for the Abi/wave protein complex in T cell receptor-mediated proliferation and cytoskeletal remodeling.

BACKGROUND: The molecular reorganization of signaling molecules after T cell receptor (TCR) activation is accompanied by polymerization of actin at the site of contact between a T cell and an antigen-presenting cell (APC), as well as extension of actin-rich lamellipodia around the APC. Actin polymerization is critical for the fidelity and efficiency of the T cell response to antigen. The ability of T cells to polymerize actin is critical for several steps in T cell activation including TCR clustering, mature immunological synapse formation, calcium flux, IL-2 production, and proliferation. Activation of the Rac GTPase has been linked to regulation of actin polymerization after TCR stimulation. However, the molecules required for TCR-mediated actin polymerization downstream of activated Rac have remained elusive. Here we identify a novel role for the Abi/Wave protein complex, which signals downstream of activated Rac, in the regulation of actin polymerization and T cell activation in response to TCR stimulation. RESULTS: Here we show that Abi and Wave rapidly translocate from the T cell cytoplasm to the T cell:B cell contact site in the presence of antigen. Abi and Wave colocalize with actin at the T cell:B cell conjugation site. Moreover, Wave and Abi are necessary for actin polymerization after T cell activation, and loss of Abi proteins in mice impairs TCR-induced cell proliferation and IL-2 production in primary T cells. Significantly, the impairment in actin polymerization in cells lacking Abi proteins is due to the inability of Wave proteins to localize to the T cell:B cell contact site in the presence of antigen, rather than the destabilization of the components of the Wave protein complex. CONCLUSIONS: The Abi/Wave complex is a novel regulator of TCR-mediated actin dynamics, IL-2 production, and proliferation.

Loss of type III transforming growth factor beta receptor expression increases motility and invasiveness associated with epithelial to mesenchymal transition during pancreatic cancer progression.

Epithelial to mesenchymal transitions (EMTs) contribute to increases in cellular motility and invasiveness during embryonic development and tumorigenesis. The transforming growth factor beta (TGF-beta) signaling pathway is a key regulator of EMT. The TGF-beta superfamily coreceptor, the type III TGF-beta receptor (TbetaRIII or betaglycan), is required for EMT during embryonic heart development and palate fusion. Here, we establish that in a pancreatic cancer model of EMT, TbetaRIII expression is specifically lost during EMT at the mRNA and protein levels, whereas levels of the TGF-beta type I and type II receptors are maintained at the mRNA level. Loss of TbetaRIII expression at the protein level precedes the loss of E-cadherin and cytoskeletal reorganization during early stages of EMT. However, maintaining TbetaRIII expression does not block these aspects of EMT, but instead suppresses the increased motility and invasiveness associated with EMT. Reciprocally, shRNA-mediated knockdown of endogenous TbetaRIII increases cellular motility without affecting Snail or E-cadherin levels. The ability of TbetaRIII to suppress motility and invasiveness does not depend on its cytoplasmic domain or its coreceptor function. Instead, this suppression of invasion is partially mediated by ectodomain shedding of TbetaRIII, generating soluble TbetaRIII (sTbetaRIII). In human pancreatic cancer specimens, TbetaRIII expression decreases at both the mRNA and protein levels, with the degree of loss correlating with worsening tumor grade. Taken together, these studies support a role for loss of TbetaRIII expression during the EMT of pancreatic cancer progression, with a specific role for sTbetaRIII in suppressing EMT-associated increases in motility and invasion.

Abl family kinases regulate endothelial barrier function in vitro and in mice.

The maintenance of endothelial barrier function is essential for normal physiology, and increased vascular permeability is a feature of a wide variety of pathological conditions, leading to complications including edema and tissue damage. Use of the pharmacological inhibitor imatinib, which targets the Abl family of non-receptor tyrosine kinases (Abl and Arg), as well as other tyrosine kinases including the platelet-derived growth factor receptor (PDGFR), Kit, colony stimulating factor 1 receptor (CSF1R), and discoidin domain receptors, has shown protective effects in animal models of inflammation, sepsis, and other pathologies characterized by enhanced vascular permeability. However, the imatinib targets involved in modulation of vascular permeability have not been well-characterized, as imatinib inhibits multiple tyrosine kinases not only in endothelial cells and pericytes but also immune cells important for disorders associated with pathological inflammation and abnormal vascular permeability. In this work we employ endothelial Abl knockout mice to show for the first time a direct role for Abl in the regulation of vascular permeability in vivo. Using both Abl/Arg-specific pharmacological inhibition and endothelial Abl knockout mice, we demonstrate a requirement for Abl kinase activity in the induction of endothelial permeability by vascular endothelial growth factor both in vitro and in vivo. Notably, Abl kinase inhibition also impaired endothelial permeability in response to the inflammatory mediators thrombin and histamine. Mechanistically, we show that loss of Abl kinase activity was accompanied by activation of the barrier-stabilizing GTPases Rac1 and Rap1, as well as inhibition of agonist-induced Ca(2+) mobilization and generation of acto-myosin contractility. In all, these findings suggest that pharmacological targeting of the Abl kinases may be capable of inhibiting endothelial permeability induced by a broad range of agonists and that use of Abl kinase inhibitors may have potential for the treatment of disorders involving pathological vascular leakage.

Breast cancer cells induce osteoblast apoptosis: a possible contributor to bone degradation.

Breast cancer cells exhibit a predilection for metastasis to bone. There, the metastases usually bring about bone loss with accompanying pain and loss of function. One way that breast cancer cells disrupt the normal pattern of bone remodeling is by activating osteoclasts, the bone degrading cells. Nevertheless, targeting the osteoclasts does not cure the disease or result in bone repair. These observations indicate that osteoblast function also may be compromised. The objective of this study was to investigate the interaction of metastatic breast cancer cells with osteoblasts. Human metastatic breast cancer cells, MDA-MB-435 or MDA-MB-231, or their conditioned media were co-cultured with a human osteoblast line hFOB1.19. The breast cancer cells caused an increase in the prevalence of apoptotic osteoblasts. Apoptotic osteoblasts detected by the TUNEL assay or by caspase activity increased approximately two to fivefold. This increase was not seen with non-metastatic MDA-MB-468 cells. In an investigation of the mechanism, it was determined that the hFOB1.19 cells expressed fas and that fas was functional. Likewise the hFOB1.19 cells were susceptible to TNF-alpha, but this cytokine was not detected in the conditioned medium of the breast cancer cells. This study indicates that osteoblasts are the target of breast cancer cell-induced apoptosis, but fas/fas-ligand and TNF-alpha, two common initiators of cell death, are probably not involved in this aspect of the metastases/bone cell axis. There are several mechanisms that remain to be explored in order to determine how breast cancer cells bring about osteoblast apoptosis. Even though the specific initiator of apoptosis remains to be identified, the results of this study suggest that the mechanism is likely to be novel.