Regulation of Planar Cell Polarity by Smurf Ubiquitin Ligases

SummaryPlanar cell polarity (PCP) is critical for morphogenesis in metazoans. PCP in vertebrates regulates stereocilia alignment in neurosensory cells of the cochlea and closure of the neural tube through convergence and extension movements (CE). Noncanonical Wnt morphogens regulate PCP and CE in vertebrates, but the molecular mechanisms remain unclear. Smurfs are ubiquitin ligases that regulate signaling, cell polarity and motility through spatiotemporally restricted ubiquitination of diverse substrates. Here, we report an unexpected role for Smurfs in controlling PCP and CE. Mice mutant for Smurf1 and Smurf2 display PCP defects in the cochlea and CE defects that include a failure to close the neural tube. Further, we show that Smurfs engage in a noncanonical Wnt signaling pathway that targets the core PCP protein Prickle1 for ubiquitin-mediated degradation. Our work thus uncovers ubiquitin ligases in a mechanistic link between noncanonical Wnt signaling and PCP/CE

Tumour-stroma Signalling in Cancer Cell Motility and Metastasis

The tumour-associated stroma, consisting of fibroblasts, inflammatory cells, vasculature and extracellular matrix proteins, plays a critical role in tumour growth, but how it regulates cancer cell migration and metastasis is poorly understood. The Wnt-planar cell polarity (PCP) pathway regulates convergent extension movements in vertebrate development. However, it is unclear whether this pathway also functions in cancer cell migration. In addition, the factors that mobilize long-range signalling of Wnt morphogens, which are tightly associated with the plasma membrane, have yet to be completely characterized. Here, I show that fibroblasts secrete membrane microvesicles of endocytic origin, termed exosomes, which promote tumour cell protrusive activity, motility and metastasis via the exosome component Cd81. In addition, I demonstrate that fibroblast exosomes activate autocrine Wnt-PCP signalling in breast cancer cells as detected by the association of Wnt with Fzd receptors and the asymmetric distribution of Fzd-Dvl and Vangl-Pk complexes in exosome-stimulated cancer cell protrusive structures. Moreover, I show that Pk expression in breast cancer cells is essential for fibroblast-stimulated cancer cell metastasis. Lastly, I reveal that trafficking in cancer cells promotes tethering of autocrine Wnt11 to fibroblast exosomes. These studies further our understanding of the role of the tumour-associated stroma in cancer metastasis and bring us closer to a more targeted approach for the treatment of cancer spread.Ph

The extracellular domain of the TGF\u3b2 type II receptor regulates membrane raft partitioning

Cell-surface TGF\u3b2 (transforming growth factor \u3b2) receptors partition into membrane rafts and the caveolin-positive endocytic compartment by an unknown mechanism. In the present study, we investigated the determinant in the TGF\u3b2 type II receptor (T\u3b2RII) that is necessary for membrane raft/caveolar targeting. Using subcellular fractionation and immunofluorescence microscopy techniques, we demonstrated that the extracellular domain of T\u3b2RII mediates receptor partitioning into raft and caveolin-positive membrane domains. Pharmacological perturbation of glycosylation using tunicamycin or the mutation of Mgat5 [mannosyl(\u3b1-1,6)-glycoprotein \u3b2-1,6-N-acetylglucosaminyltransferase V] activity interfered with the raft partitioning of T\u3b2RII. However, this was not due to the glycosylation state of T\u3b2RII, as a non-glycosylated T\u3b2RII mutant remained enriched in membrane rafts. This suggested that other cell-surface glycoproteins associate with the extracellular domain of T\u3b2RII and direct their partitioning in membrane raft domains. To test this we analysed a GMCSF (granulocyte/macrophage colony-stimulating factor)\u2013T\u3b2RII chimaeric receptor, which contains a glycosylated GMCSF extracellular domain fused to the transmembrane and intracellular domains of T\u3b2RII. This chimaeric receptor was found to be largely excluded from membrane rafts and caveolin-positive structures. Our results indicate that the extracellular domain of T\u3b2RII mediates receptor partitioning into membrane rafts and efficient entrance into caveolin-positive endosomes.Peer reviewed: YesNRC publication: Ye

Exosomes Mediate Mobilization of Autocrine Wnt10b to Promote Axonal Regeneration in the Injured CNS

Developing strategies that promote axonal regeneration within the injured CNS is a major therapeutic challenge, as axonal outgrowth is potently inhibited by myelin and the glial scar. Although regeneration can be achieved using the genetic deletion of PTEN, a negative regulator of the mTOR pathway, this requires inactivation prior to nerve injury, thus precluding therapeutic application. Here, we show that, remarkably, fibroblast-derived exosomes (FD exosomes) enable neurite growth on CNS inhibitory proteins. Moreover, we demonstrate that, upon treatment with FD exosomes, Wnt10b is recruited toward lipid rafts and activates mTOR via GSK3β and TSC2. Application of FD exosomes shortly after optic nerve injury promoted robust axonal regeneration, which was strongly reduced in Wnt10b-deleted animals. This work uncovers an intercellular signaling pathway whereby FD exosomes mobilize an autocrine Wnt10b-mTOR pathway, thereby awakening the intrinsic capacity of neurons for regeneration, an important step toward healing the injured CNS

Effects of fire on humic and lipid fractions in a Dystric Xerochrept in Spain

Fire-induced changes in humic and lipid soil fractions were assessed by two approaches. Comparisons were made of the nature and amounts of the two fractions in samples of aDystricXerochrept under two pine stands, one that had been burned two years earlier and one that had not. Further comparisons were made of humic and lipidfractions in a soil sample before and after heating in the laboratory. Separation and identification of the compounds in these soil fractions were carried out by preparative liquid chromatography followed by GC-MS in the case of lipids; the humic acids were previously degraded by successive treatments with sodium persulphate and potassium permanganate. The greatest differences were in the distribution patterns of soil lipids (alkanes, fatty acids): accumulation of the homologues of lower molecular weight () was dominant in the post-fire samples. For soil resin acids, these samples had higher values for dehydroabietic and secodehydroabietic acids and lower ones for pimaric acid. The degradative studies on the humic acids showed that the relative yields of aromatic products were comparatively higher in the samples after burning. Alkanoic diacids were found to be the least resistant to heating, whereas greater amounts of alkanes in the less condensed polymer structures of the humic acids were observed in the samples after burning. The relative amounts and distribution patterns of the fatty acids released showed no great differences in the humic acids.Peer reviewe