Nesprin-2 interacts with α-Catenin and regulates Wnt signaling at the nuclear envelope.

Nesprins and emerin are structural nuclear envelope proteins that tether nuclei to the cytoskeleton. In this work, we identified the cytoskeleton-associated α-N/E-catenins as novel nesprin-2-binding partners. The association involves the C termini of nesprin-2 giant and α-N/E-catenins. α-E/T/N-catenins are known primarily for their roles in cadherin-mediated cell-cell adhesion. Here, we show that, in addition, α-catenin forms complexes with nesprin-2 that include β-catenin and emerin. We demonstrate that the depletion of nesprin-2 reduces both the amount of active β-catenin inside the nucleus and T-cell factor/lymphoid-enhancing factor-dependent transcription. Taken together, these findings suggest novel nesprin-2 functions in cellular signaling. Moreover, we propose that, in contrast to emerin, nesprin-2 is a positive regulator of the Wnt signaling pathway

Role of von Hippel-Lindau protein in fibroblast proliferation and fibrosis.

Idiopathic pulmonary fibrosis (IPF) is characterized by exaggerated fibroblast proliferation and accumulation of collagens and fibronectin. The extracellular fibronectin and collagen network is regulated by von Hippel-Lindau protein (pVHL). However, it is unknown whether pVHL contributes to pulmonary fibrosis. We found that lungs from patients with IPF expressed increased levels of pVHL in fibroblastic foci. Bleomycin treatment also induced pVHL in lung fibroblasts, but not in alveolar type II cells. Overexpression of pVHL increased lung fibroblast proliferation, protein abundance of fibronectin and collagen, and extracellular fibronectin. In addition, overexpression of pVHL induced expression of the α5 integrin subunit. Overexpression of pVHL did not alter hypoxia-inducible factor luciferase reporter activity and mRNA expression of vascular endothelial growth factor. Fibroblasts overexpressing pVHL were more sensitive to RGD peptide-mediated reduction in proliferation. Activating α5 and β1 integrin increased proliferation of fibroblasts overexpressing pVHL and those cells were more resistant to the inhibition of α5 integrin. Overexpression of pVHL also increased activation of focal adhesion kinase (FAK). Moreover, suppression of pVHL prevented TGF-β1-induced proliferation of mouse embryonic fibroblasts. Taken together, our results indicate that elevated expression of pVHL results in the aberrant fibronectin expression, activation of integrin/FAK signaling, fibroblast proliferation, and fibrosis.-Zhou, Q., Pardo, A., Königshoff, M., Eickelberg, O., Budinger, G. R. S., Thavarajah, K., Gottardi, C. J., Jones, J., Varga, J., Selman, M., Sznajder, J. I., Raj, J. U., Zhou, G. Role of von Hippel-Lindau protein in fibroblast proliferation and fibrosis

Symplekin, a Constitutive Protein of Karyo- and Cytoplasmic Particles Involved in mRNA Biogenesis in Xenopus laevis Oocytes

Symplekin is a dual location protein that has been localized to the cytoplasmic plaques of tight junctions but also occurs in the form of interchromatin particles in the karyoplasm. Here we report the identification of two novel and major symplekin-containing protein complexes in both the karyo- and the cytoplasm of Xenopus laevis oocytes. Buffer-extractable fractions from the karyoplasm of stage IV–VI oocytes contain an 11S particle, prepared by immunoselection and sucrose gradient centrifugation, in which symplekin is associated with the subunits of the cleavage and polyadenylation specificity factor (CPSF). Moreover, in immunofluorescence microscopy nuclear symplekin colocalizes with protein CPSF-100 in the “Cajal bodies.” However, symplekin is also found in cytoplasmic extracts of enucleated oocytes and egg extracts, where it occurs in 11S as well as in ca. 65S particles, again in association with CPSF-100. This suggests that, in X. laevis oocytes, symplekin is possibly involved in both processes, 3′-end processing of pre-mRNA in the nucleus and regulated polyadenylation in the cytoplasm. We discuss the possible occurrence of similar symplekin-containing particles involved in mRNA metabolism in the nucleus and cytoplasm of other kinds of cells, also in comparison with the nuclear forms of other dual location proteins in nuclei and cell junctions