The planar cell polarity protein VANGL2 coordinates remodeling of the extracellular matrix.

Understanding how planar cell polarity (PCP) is established, maintained, and coordinated in migrating cell populations is an important area of research with implications for both embryonic morphogenesis and tumor cell invasion. We recently reported that the PCP protein Vang-like 2 (VANGL2) regulates the endocytosis and cell surface level of membrane type-1 matrix metalloproteinase (MMP14 or MT1-MMP). Here, we further discuss these findings in terms of extracellular matrix (ECM) remodeling, cell migration, and zebrafish gastrulation. We also demonstrate that VANGL2 function impacts the focal degradation of ECM by human cancer cells including the formation or stability of invadopodia. Together, our findings implicate MMP14 as a downstream effector of VANGL2 signaling and suggest a model whereby the regulation of pericellular proteolysis is a fundamental aspect of PCP in migrating cells.

VANGL2 regulates membrane trafficking of MMP14 to control cell polarity and migration.

Planar cell polarity (PCP) describes the polarized orientation of cells within the plane of a tissue. Unlike epithelial PCP, the mechanisms underlying PCP signaling in migrating cells remain undefined. Here, the establishment of PCP must be coordinated with dynamic changes in cell adhesion and extracellular matrix (ECM) organization. During gastrulation, the membrane type-1 matrix metalloproteinase (MT1-MMP or MMP14) is required for PCP and convergence and extension cell movements. We report that the PCP protein Vang-like 2 (VANGL2) regulates the endocytosis and cell-surface availability of MMP14 in manner that is dependent on focal adhesion kinase. We demonstrate that zebrafish trilobite/vangl2 mutant embryos exhibit increased Mmp14 activity and decreased ECM. Furthermore, in vivo knockdown of Mmp14 partially rescues the Vangl2 loss-of-function convergence and extension phenotype. This study identifies a mechanism linking VANGL2 with MMP14 trafficking and suggests that establishment of PCP in migrating gastrula cells requires regulated proteolytic degradation or remodeling of the ECM. Our findings implicate matrix metalloproteinases as downstream effectors of PCP and suggest a broadly applicable mechanism whereby VANGL2 affects diverse morphogenetic processes.

Altered manganese homeostasis and manganese toxicity in a Huntington's disease striatal cell model are not explained by defects in the iron transport system.

Expansion of a polyglutamine tract in Huntingtin (Htt) leads to the degeneration of medium spiny neurons in Huntington's disease (HD). Furthermore, the HTT gene has been functionally linked to iron (Fe) metabolism, and HD patients show alterations in brain and peripheral Fe homeostasis. Recently, we discovered that expression of mutant HTT is associated with impaired manganese (Mn) uptake following overexposure in a striatal neuronal cell line and mouse model of HD. Here we test the hypothesis that the transferrin receptor (TfR)-mediated Fe uptake pathway is responsible for the HD-associated defects in Mn uptake. Western blot analysis showed that TfR levels are reduced in the mutant STHdh(Q111/Q111) striatal cell line, whereas levels of the Fe and Mn transporter, divalent metal transporter 1 (DMT1), are unchanged. To stress the Fe transport system, we exposed mutant and wild-type cells to elevated Fe(III), which revealed a subtle impairment in net Fe uptake only at the highest Fe exposures. In contrast, the HD mutant line exhibited substantial deficits in net Mn uptake, even under basal conditions. Finally, to functionally evaluate a role for Fe transporters in the Mn uptake deficit, we examined Mn toxicity in the presence of saturating Fe(III) levels. Although Fe(III) exposure decreased Mn neurotoxicity, it did so equally for wild-type and mutant cells. Therefore, although Fe transporters contribute to Mn uptake and toxicity in the striatal cell lines, functional alterations in this pathway are insufficient to explain the strong Mn resistance phenotype of this HD cell model.

Disease-toxicant screen reveals a neuroprotective interaction between Huntington's disease and manganese exposure.

Recognizing the similarities between Huntington's disease (HD) pathophysiology and the neurotoxicology of various metals, we hypothesized that they may exhibit disease-toxicant interactions revealing cellular pathways underlying neurodegeneration. Here, we utilize metals and the STHdh mouse striatal cell line model of HD to perform a gene-environment interaction screen. We report that striatal cells expressing mutant Huntingtin exhibit elevated sensitivity to cadmium toxicity and resistance to manganese toxicity. This neuroprotective gene-environment interaction with manganese is highly specific, as it does not occur with iron, copper, zinc, cobalt, cadmium, lead, or nickel ions. Analysis of the Akt cell stress signaling pathway showed diminished activation with manganese exposure and elevated activation after cadmium exposure in the mutant cells. Direct examination of intracellular manganese levels found that mutant cells have a significant impairment in manganese accumulation. Furthermore, YAC128Q mice, a HD model, showed decreased total striatal manganese levels following manganese exposure relative to wild-type mice. Thus, this disease-toxicant interaction screen has revealed that expression of mutant Huntingtin results in heightened sensitivity to cadmium neurotoxicity and a selective impairment of manganese accumulation.

Neurotrophin receptor interacting factor (NRIF) is an essential mediator of apoptotic signaling by the p75 neurotrophin receptor.

Activation of the p75 neurotrophin receptor leads to a variety of effects within the nervous system, including neuronal apoptosis. Both c-Jun N-terminal kinase (JNK) and the tumor suppressor p53 have been reported to be critical for this receptor to induce cell death; however, the mechanisms by which p75 activates these pathways is undetermined. Here we report that the neurotrophin receptor interacting factor (NRIF) is necessary for p75-dependent JNK activation and apoptosis. Upon nerve growth factor withdrawal, nrif-/- sympathetic neurons underwent apoptosis, whereas p75-mediated death was completely abrogated. The lack of cell death correlated with a lack of JNK activation in the nrif-/- neurons, suggesting that NRIF is a selective mediator for p75-dependent JNK activation and apoptosis. Moreover, we document that NRIF expression is sufficient to induce cell death through a mechanism that requires p53. Taken together, these results establish NRIF as an essential component of the p75 apoptotic pathway.