The Abi/Wave complex is a novel regulator of TCR-mediated actin dynamics, IL-2 production, and proliferation.

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.

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 Ca2+ 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.

No abstract