Putting the brakes on cancer cell migration

Junctional Adhesion Molecule A (JAM-A) is a member of the Ig superfamily of membrane proteins expressed in platelets, leukocytes, endothelial cells and epithelial cells. We have previously shown that in endothelial cells, JAM-A regulates basic fibroblast growth factor, (FGF-2)-induced angiogenesis via augmenting endothelial cell migration. Recently, we have revealed that in breast cancer cells, down-regulation of JAM-A enhances cancer cell migration and invasion. Further, ectopic expression of JAM-A in highly metastatic MDA-MB-231 cells attenuates cell migration, and down-regulation of JAM-A in low-metastatic T47D cells enhance migration. Interestingly, JAM-A expression is greatly diminished as breast cancer disease progresses. The molecular mechanism of this function of JAM-A is beyond its well-characterized barrier function at the tight junction. Our results point out that JAM-A differentially regulates migration of endothelial and cancer cells.     

Putting the brakes on cytokinesis with alpha-actinin

Although signal transduction pathways provide spatiotemporal control of cytokinesis, additional regulation likely occurs through complex cytoskeletal network interactions. In this issue of Developmental Cell, Mukhina et al. (2007) show that myosin-II modulates the cortical lifetime of the actin crosslinker alpha-actinin, which in turn tunes actin filament dynamics, thereby controlling furrow ingression.     

Putting the brakes on the unfolded protein response

The unfolded protein response is an ancient cellular pathway for rapidly responding to endoplasmic reticulum stress. Two studies in this issue (Rubio et al. 2011. J. Cell. Biol. doi:10.1083/jcb.201007077 and Chawla et al. 2011. J. Cell. Biol. doi:10.1083/jcb.201008071) provide insight into how the unfolded protein response is tamped down to restore normal endoplasmic reticulum function. Although both papers implicate the Ire1 kinase domain as the key effector of the off-switch mechanism, alternate models for how this is achieved are proposed.     

Removing the brakes on cell identity

In this issue of Developmental Cell, Dhawan et?al. (2011) show that deletion of the Dnmt1 DNA methyltransferase gene in pancreatic insulin-producing cells makes these cells convert into glucagon-producing cells. This suggests that manipulation of a general epigenetic mechanism may be used to redirect cell fates.     

Mechanism of fibronectin-mediated cell migration: dependence or independence of cell migration susceptibility on RGDS-directed receptor (integrin)

Cell migration on fibronectin (FN)-coated substrata was studied using 10 cell lines, of which only 2 showed clear enhancement and 1 showed marginal enhancement of cell migration. The migration of the other 7 cell lines was not affected on FN-coated substrata, although they all showed FN-dependent cell adhesion. The migration-enhancing activity of FN was found in the fragment including the cell-adhesion and Hep-2 domains, but not other domains (Hep-1/Fib-1, Gel, Fib-2). No difference in the migration-enhancing effect was seen among FNs from plasma, fibroblasts, or transformed cells. FN-dependent cell migration was inhibited by polyclonal antibodies directed to the C-terminal half region including the cell binding domain, but not by antibodies directed to five other domains. Since these results indicated that FN-mediated cell migration could be controlled by the cell-adhesion domain of FN and its receptor, studies were then focused on the effect of antibodies directed to receptors for FN and collagen, and on the effect of tetrapeptide sequences recognized by these receptors. It was found that (i) cell migration on FN-coated surfaces was specifically inhibited by anti-FN receptor antibody P1F8 but not by anticollagen receptor antibody P1H5; (ii) the migration was strongly inhibited by Arg-Gly-Asp-Ser but not by other oligopeptide sequences. However, the majority of those cell lines not susceptible to FN-dependent cell migration were characterized by having FN receptors and the ability to adhere on FN-coated matrix. Based on these findings, it was concluded that FN-dependent cell migration shares the same recognition mechanism as FN-dependent cell adhesion, but that the majority of cell lines not exhibiting FN-dependent migration still show FN-dependent cell adhesion and express the FN receptor (integrin); i.e., cell migration and adhesion involve the same receptor and the same FN loci, but migration is controlled by still-unidentified cellular factors which determine the susceptibility of the cell to the dynamic function of the FN receptor (integrin) unit.     

RAC1 activation mediates Twist1-induced cancer cell migration

Epithelial-mesenchymal transition (EMT), which is characterized by the suppression of the adhesion protein E-cadherin, is a crucial process that promotes metastasis and stem-like properties of cancer cells. However, the dissociation of cellular aggregates is not sufficient to explain why cancer cells move, and the motile nature of cancer cells undergoing EMT remains elusive. Here, we identify a mechanism in which the EMT inducer Twist1 elicits cancer cell movement through activation of RAC1. Twist1 cooperates with BMI1 to suppress let-7i expression, which results in upregulation of NEDD9 and DOCK3, leading to RAC1 activation and enabling mesenchymal-mode movement in three-dimensional environments. Moreover, the suppression of let-7i contributes to Twist1-induced stem-like properties. Clinically, activation of the Twist1-let-7i-NEDD9 axis in head and neck cancer patients correlates with tumour invasiveness and worse outcome. Our results uncover an essential mechanism to explain how Twist1 induces the motile stem-like cancer cell phenotype beyond simply suppressing E-cadherin.     

Tenascin-C enhances pancreatic cancer cell growth and motility and affects cell adhesion through activation of the integrin pathway

Background

Pancreatic cancer (PDAC) is characterized by an abundant fibrous tissue rich in Tenascin-C (TNC), a large ECM glycoprotein mainly synthesized by pancreatic stellate cells (PSCs). In human pancreatic tissues, TNC expression increases in the progression from low-grade precursor lesions to invasive cancer. Aim of this study was the functional characterization of the effects of TNC on biologic relevant properties of pancreatic cancer cells.

Methods

Proliferation, migration and adhesion assays were performed on pancreatic cancer cell lines treated with TNC or grown on a TNC-rich matrix. Stable transfectants expressing the large TNC splice variant were generated to test the effects of endogenous TNC. TNC-dependent integrin signaling was investigated by immunoblotting, immunofluorescence and pharmacological inhibition.

Results

Endogenous TNC promoted pancreatic cancer cell growth and migration. A TNC-rich matrix also enhanced migration as well as the adhesion to the uncoated growth surface of poorly differentiated cell lines. In contrast, adhesion to fibronectin was significantly decreased in the presence of TNC. The effects of TNC on cell adhesion were paralleled by changes in the activation state of paxillin and Akt.

Conclusion

TNC affects proliferation, migration and adhesion of poorly differentiated pancreatic cancer cell lines and might therefore play a role in PDAC spreading and metastasis in vivo.     

The TMEFF2 tumor suppressor modulates integrin expression,RhoA activation and migration of prostate cancer cells

Cell adhesion and migration play important roles in physiological and pathological states, including embryonic development and cancer invasion and metastasis. The type I transmembrane protein with epidermal growth factor and two follistatin motifs 2 (TMEFF2) is expressed mainly in brain and prostate and its expression is deregulated in prostate cancer. We have previously shown that TMEFF2 can function as a tumor suppressor by inhibiting cell migration and invasion of prostate cells. However, the molecular mechanisms involved in this inhibition are not clear. In this study we demonstrate that TMEFF2 affects cell adhesion and migration of prostate cancer cells and that this effect correlates with changes in integrin expression and RhoA activation. Deletion of a 13 basic-rich amino acid region in the cytoplasmic domain of TMEFF2 prevented these effects. Overexpression of TMEFF2 reduced cell attachment and migration on vitronectin and caused a concomitant decrease in RhoA activation, stress fiber formation and expression of αv, β1 and β3 integrin subunits. Conversely, TMEFF2 interference in 22Rv1 prostate cancer cells resulted in an increased integrin expression. Results obtained with a double TRAMP/TMEFF2 transgenic mouse also indicated that TMEFF2 expression reduced integrin expression in the mouse prostate. In summary, the data presented here indicate an important role of TMEFF2 in regulating cell adhesion and migration that involves integrin signaling and is mediated by its cytoplasmic domain.     

Proline-rich tyrosine kinase 2 and Rac activation by chemokine and integrin receptors controls NK cell transendothelial migration

Protein tyrosine kinase activation is an important requisite for leukocyte migration. Herein we demonstrate that NK cell binding to endothelium activates proline-rich tyrosine kinase 2 (Pyk-2) and the small GTP binding protein Rac that are coupled to integrin and chemokine receptors. Chemokine-mediated, but not integrin-mediated, Pyk-2 and Rac activation was sensitive to pretreatment of NK cells with pertussis toxin, a pharmacological inhibitor of G(i) protein-coupled receptors. Both Pyk-2 and Rac are functionally involved in chemokine-induced NK cell migration through endothelium or ICAM-1 or VCAM-1 adhesive proteins, as shown by the use of recombinant vaccinia viruses encoding dominant negative mutants of Pyk-2 and Rac. Moreover, we found that Pyk-2 is associated with the Rac guanine nucleotide exchange factor Vav, which undergoes tyrosine phosphorylation upon integrin triggering. Finally, we provide direct evidence for the involvement of Pyk-2 in the control of both chemokine- and integrin-mediated Rac activation. Collectively, our results indicate that Pyk-2 acts as a receptor-proximal link between integrin and chemokine receptor signaling, and the Pyk-2/Rac pathway plays a pivotal role in the control of NK cell transendothelial migration.