MT1-MMP-dependent invasion is regulated by TI-VAMP/VAMP7

Proteolytic degradation of the extracellular matrix (ECM) is one intrinsic property of metastatic tumor cells to breach tissue barriers and to disseminate into different tissues. This process is initiated by the formation of invadopodia, which are actin-driven, finger-like membrane protrusions. Yet, little is known on how invadopodia are endowed with the functional machinery of proteolytic enzymes [1, 2]. The key protease MT1-MMP (membrane type 1-matrix metalloproteinase) confers proteolytic activity to invadopodia and thus invasion capacity of cancer cells [3-6]. Here, we report that MT1-MMP-dependent matrix degradation at invadopodia is regulated by the v-SNARE TI-VAMP/VAMP7, hence providing the molecular inventory mediating focal degradative activity of cancer cells. As observed by TIRF microscopy, MT1-MMP-mCherry and GFP-VAMP7 were simultaneously detected at proteolytic sites. Functional ablation of VAMP7 decreased the ability of breast cancer cells to degrade and invade in a MT1-MMP-dependent fashion. Moreover, the number of invadopodia was dramatically decreased in VAMP7- and MT1-MMP-depleted cells, indicative of a positive-feedback loop in which the protease as a cargo of VAMP7-targeted transport vesicles regulates maturation of invadopodia. Collectively, these data point to a specific role of VAMP7 in delivering MT1-MMP to sites of degradation, maintaining the functional machinery required for invasion.     

Death by splicing: tumor suppressor RBM5 freezes splice-site pairing

In a recent issue of Molecular Cell, Bonnal et al. (2008) demonstrate that the tumor suppressor gene RBM5 regulates alternative splicing of Fas pre-mRNA by interfering with splice-site pairing.     

Targeting, Capture, and Stabilization of Microtubules at Early Focal Adhesions

By co-injecting fluorescent tubulin and vinculin into fish fibroblasts we have revealed a “cross talk” between microtubules and early sites of substrate contact. This mutuality was first indicated by the targeting of vinculin-rich foci by microtubules during their growth towards the cell periphery. In addition to passing directly over contact sites, the ends of single microtubules could be observed to target several contacts in succession or the same contact repetitively, with intermittent withdrawals. Targeting sometimes involved side-stepping, or the major re-routing of a microtubule, indicative of a guided, rather than a random process. The paths that microtubules followed into contacts were unrelated to the orientation of stress fiber assemblies and targeting occurred also in mouse fibroblasts that lacked a system of intermediate filaments. Further experiments with microtubule inhibitors showed that adhesion foci can: (a) capture microtubules and stabilize them against disassembly by nocodazole; and (b), act as preferred sites of microtubule polymerization, during either early recovery from nocodazole, or brief treatment with taxol. From these and other findings we speculate that microtubules are guided into substrate contact sites and through the motor-dependent delivery of signaling molecules serve to modulate their development. It is further proposed this modulation provides the route whereby microtubules exert their influence on cell shape and polarity.     

Characterization of soluble vs membrane-bound human placental 5'-nucleotidase

Three forms of 5'-nucleotidase purified from human placenta (two membrane-bound forms, one sensitive and one resistant to cleavage by phosphatidylinositol-specific phospholipase C, as well as a soluble form) had the same molecular weight before (73,000 Da) and after (56,000 Da) digestion with N-glycosidase F and showed similar amino acid compositions, N-terminal amino acid sequences, and KMs for IMP (9.6 to 11.9 microM). Thus, these three forms of 5'-nucleotidase appear to have very similar structures. The form sensitive to phosphatidylinositol-specific phospholipase C contained nearly 1 mol myo-inositol/mol of protein as determined by mass spectrometry, indicating a glycosyl phosphatidylinositol membrane anchor. Soluble 5'-nucleotidase contained a similar quantity of myo-inositol, suggesting that it was previously membrane-anchored via glycosyl phosphatidylinositol. The form resistant to phosphatidylinositol-specific phospholipase C contained less myo-inositol, leaving open the possibility of a third form of 5'-nucleotidase with a conventional transmembrane anchor.     

Moulting starvation in emperor penguin (Aptenodytes forsten) chicks

Summary The moult fast in emperor penguin (Aptenodytes forsteri) chicks was studied during January 1990 at Drescher Inlet, eastern Weddell Sea. In early January feeding of the chicks had stopped and about 4,000–5,000 chicks were in the inlet. The number of starving chicks decreased rapidly until 26 January when all chicks had either left the inlet or died. Mean body mass loss of starving chicks was 257 g/day and the evaluated specific daily mass loss was 25 g/kg body mass. The critical body mass, i.e. the mass below which chicks die, during moulting starvation was estimated to be 4 kg. Mean body mass was higher and mass loss lower in chicks at more advanced moult stages. Chicks left the inlet before moult was completed, although the sea-ice was still stable.     

Cdc42 is not essential for filopodium formation, directed migration, cell polarization, and mitosis in fibroblastoid cells

Cdc42 is a small GTPase involved in the regulation of the cytoskeleton and cell polarity. To test whether Cdc42 has an essential role in the formation of filopodia or directed cell migration, we generated Cdc42-deficient fibroblastoid cells by conditional gene inactivation. We report here that loss of Cdc42 did not affect filopodium or lamellipodium formation and had no significant influence on the speed of directed migration nor on mitosis. Cdc42-deficient cells displayed a more elongated cell shape and had a reduced area. Furthermore, directionality during migration and reorientation of the Golgi apparatus into the direction of migration was decreased. However, expression of dominant negative Cdc42 in Cdc42-null cells resulted in strongly reduced directed migration, severely reduced single cell directionality, and complete loss of Golgi polarization and of directionality of protrusion formation toward the wound, as well as membrane blebbing. Thus, our data show that besides Cdc42 additional GTPases of the Rho-family, which share GEFs with Cdc42, are involved in the establishment and maintenance of cell polarity during directed migration.     

Southern rockhopper penguin Eudyptes chrysocome chrysocome foraging at Possession Island

The foraging ecology of rockhopper penguins was studied at Possession Island, southern Indian Ocean, by counting the number of birds departing from and arriving at colonies over the course of the day and by equipping three birds with time/depth loggers, one of which was recovered having recorded a total of 12 days foraging activity. Both the counts and the results from the diving behaviour showed that the birds foraged exclusively diurnally. Maximum dive depth was 66 m although most time was spent between 10 and 25 m, depths that did not accord with the published distribution of their principal prey as detected by nets and acoustics. Received: 29 March 1996/Accepted: 10 June 1996