SummaryCells inversely adjust the plasma membrane levels of integrins and cadherins during cell migration and cell-cell adhesion but the regulatory mechanisms that coordinate these trafficking events remain unknown. Here, we demonstrate that the small GTPase Rab35 maintains cadherins at the cell surface to promote cell-cell adhesion. Simultaneously, Rab35 supresses the activity of the GTPase Arf6 to downregulate an Arf6-dependent recycling pathway for b1-integrin and EGF receptors, resulting in inhibition of cell migration and attenuation of signaling downstream of these receptors. Importantly, the phenotypes of decreased cell adhesion and increased cell migration observed following Rab35 knock down are consistent with the epithelial-mesenchymal transition, a feature of invasive cancer cells, and we show that Rab35 expression is suppressed in a subset of cancers characterized by Arf6 hyperactivity. Our data thus identify a key molecular mechanism that efficiently coordinates the inverse intracellular sorting and cell surface levels of cadherin and integrin receptors for cell migration and differentiation.

The expression of N-cadherin (NCAD) has been shown to correlate with increased tumor cell motility and metastasis. However, NCAD-mediated adhesion is a robust phenomenon and therefore seems to be inconsistent with the "release" from intercellular adhesion required for invasion. We show that in the most invasive melanoma and brain tumor cells, altered posttranslational processing results in abundant nonadhesive precursor N-cadherin (proNCAD) at the cell surface, although total NCAD levels remain constant. We demonstrate that aberrantly processed proNCAD promotes cell migration and invasion in vitro. Furthermore, in human tumor specimens, we find high levels of proNCAD as well, supporting an overall conclusion that proNCAD and mature NCAD coexist on these tumor cell surfaces and that it is the ratio between these functionally antagonistic moieties that directly correlates with invasion potential. Our work provides insight into what may be a widespread mechanism for invasion and metastasis and challenges the current dogma of the functional roles played by classic cadherins in tumor progression.

Thrombin-activable fibrinolysis inhibitor (TAFI) has recently been identified as a positive acute phase protein in mice, an observation that may have important implications for the interaction of the coagulation, fibrinolytic, and inflammatory systems. Activated TAFI (TAFIa) inhibits fibrinolysis by removing the carboxylterminal lysines from partially degraded fibrin that are important for maximally efficient plasminogen activation. In addition, TAFIa has been shown to be capable of removing the carboxyl-terminal arginine residues from the anaphylatoxins and bradykinin, thus implying a role for the TAFI pathway in the vascular responses to inflammation. In the current study, we investigated the ability of acute phase mediators to modulate human TAFI gene expression in cultured human hepatoma (HepG2) cells. Surprisingly, we found that treatment of HepG2 cells with a combination of interleukin (IL)-1␤ and IL-6 suppressed endogenous TAFI mRNA abundance in HepG2 cells (ϳ60% decrease), while treatment with IL-1␤ or IL-6 alone had no effect. Treatment with IL-1␤ and/or IL-6 had no effect on TAFI promoter activity as measured using a luciferase reporter plasmid containing the human TAFI 5 -flanking region, whereas treatment with IL-1␤ and IL-6 in combination, but not alone, decreased the stability of the endogenous TAFI mRNA. Treatment with the synthetic glucocorticoid dexamethasone resulted in a 2-fold increase of both TAFI mRNA levels and promoter activity. We identified a functional glucocorticoid response element (GRE) in the human TAFI promoter between nucleotides ؊92 and ؊78. The GRE was capable of binding the glucocorticoid receptor, as assessed by gel mobility shift assays, and mutation of this element markedly decreased the ability of the TAFI promoter to be activated by dexamethasone.Thrombin activable fibrinolysis inhibitor (TAFI) 1 was first identified in 1989 by two independent groups as a basic carboxypeptidase present in fresh serum that was distinct from the constitutive basic carboxypeptidase N (1, 2). By virtue of the intrinsic instability of this enzyme, whose activity disappeared within 2 h upon incubation at 37°C, Hendriks et al.(1) designated the novel activity "unstable" carboxypeptidase or carboxypeptidase U (1). Campbell and Okada (2) determined that the enzyme removed arginine residues from substrates more efficiently than lysines and therefore designated it carboxypeptidase R (2). In 1991, Eaton et al. (3) isolated a cDNA encoding the zymogen form of the enzyme and found that it was highly homologous to pancreatic procarboxypeptidase B. Bajzar et al. (4) independently isolated a protein on the basis of its ability to inhibit fibrinolysis in the setting of sustained activation of the coagulation cascade; on the basis of this property, they named the protein TAFI. Amino acid sequence analysis of TAFI revealed it to be identical to plasma procarboxypeptidase B and procarboxypeptidases U and R. TAFI can be activated by thrombin (4), plasmin (5), and thrombin in complex with thrombomodulin (6), wi...