Plakophilin 1 deficiency in prostatic tumours is correlated with immune cell recruitment and controls the up‐regulation of cytokine expression post‐transcriptionally

Plakophilin (PKP1) 1 is a member of the arm‐repeat family of catenins and acts as a structural component of desmosomes, which are important stabilizers of cell–cell adhesion. Besides this, PKP1 also occurs in a non‐junctional, cytoplasmic form contributing to post‐transcriptional regulation of gene expression. Moreover, PKP1 is expressed in the prostate epithelium but its expression is frequently downregulated in prostate cancers with a more aggressive phenotype. This observation may imply a tumour‐suppressive role of PKP1. We found that, in prostatic adenocarcinomas with PKP1 deficiency, the occurrence of T‐cells, B‐cells, macrophages and neutrophils were significantly increased. In a PKP1‐deficient prostatic cancer cell line expressing IL8, these levels were statistically meaningfully reduced upon PKP1 re‐expression. When analysing prostatic PKP1 knockdown cell lines, the mRNA and protein levels of additional cytokines, namely CXCL1 and IL6, were upregulated. The effect was rescued upon re‐expression of a PKP1 RNAi‐resistant form. The corresponding mRNAs were co‐precipitated with cytoplasmic PKP1, indicating that they are components of PKP1‐containing mRNA ribonucleoprotein particles. Moreover, the mRNA half‐lives of CXCL1, IL8 and IL6 were significantly increased in PKP1‐deficient cells, showing that these mRNAs were stabilized by PKP1. In an in vitro migration assay, the higher cytokine concentrations led to higher migration rates of THP1 and PBMC cells. This finding implies that PKP1 loss of expression in vivo correlates with the recruitment of immune cells into the tumour area to set up a tumour‐specific environment. One may speculate that this newly established tumour environment has tumour‐suppressive characteristics and thereby accelerates tumour progression and metastasis

Protein Tpr is required for establishing nuclear pore-associated zones of heterochromatin exclusion

Amassments of heterochromatin in somatic cells occur in close contact with the nuclear envelope (NE) but are gapped by channel- and cone-like zones that appear largely free of heterochromatin and associated with the nuclear pore complexes (NPCs). To identify proteins involved in forming such heterochromatin exclusion zones (HEZs), we used a cell culture model in which chromatin condensation induced by poliovirus (PV) infection revealed HEZs resembling those in normal tissue cells. HEZ occurrence depended on the NPC-associated protein Tpr and its large coiled coil-forming domain. RNAi-mediated loss of Tpr allowed condensing chromatin to occur all along the NE's nuclear surface, resulting in HEZs no longer being established and NPCs covered by heterochromatin. These results assign a central function to Tpr as a determinant of perinuclear organization, with a direct role in forming a morphologically distinct nuclear sub-compartment and delimiting heterochromatin distribution

Cadherin-Catenin Complexes During Zebrafish Oogenesis: Heterotypic Junctions Between Oocytes and Follicle Cells

13 pages, 9 figuresDuring vertebrate oogenesis, the germ cells and associated somatic cells remain connected by a variety of adhering junctional complexes. However, the molecular composition of these cellular structures is largely unknown. To identify the proteins forming the heterotypic adherens junctions between oocytes and follicle cells in the zebrafish (Danio rerio), the cDNAs encoding αE-catenin and plakoglobin were isolated. Using these cDNAs, in combination with the previously isolated β-catenin cDNA, and antibodies specific for α- and β-catenin, plakoglobin, and N- and E-cadherin, we found differences in catenin and plakoglobin gene expression during oogenesis. The immunolocalization of these plaque proteins, as well as of cadherins, in the ovarian follicle indicated an enrichment of α- and β-catenin and of E-cadherin-like protein(s) in the oocyte cortex, notably at sites of oocyte-follicle cell contacts, suggesting the presence of hitherto unknown heterotypic adherens junctions between these cells. By contrast, plakoglobin and N-cadherin localization was restricted to cell-cell contacts in the follicle cell layer. During oocyte maturation, mRNAs for αE- and β-catenin and plakoglobin accumulated, and all three plaque-forming proteins were stored in unfertilized eggs, either in complexed forms with cadherins or as free cytoplasmic pools. These findings suggest possible roles of these junctional proteins during early embryogenesisPeer reviewe

Desmosomal Plakophilins in the Prostate and Prostatic Adenocarcinomas : Implications for Diagnosis and Tumor Progression

The plakophilins, members of the armadillo-repeat family, consist of three different proteins (PKP1-3) that are specifically recruited to desmosomal plaques in a highly cell type-specific manner. Using immunofluorescence, immunoelectron microscopy, and immunoblot, we found that all three plakophilins occurred in luminal and basal cells of the pseudostratified prostate epithelium. The analysis of 135 cases of prostatic adenocarcinomas grouped into tumors with low (Gleason score ≤ 6), intermediate (Gleason score 7), and high Gleason score (8 ≤ Gleason score ≤ 10) showed that the expression of PKP1 was reduced or lost in adenocarcinomas with high Gleason scores. The expression of PKP2 was unchanged in all prostatic adenocarcinomas analyzed. In contrast, PKP3 expression was increased in carcinomas with high Gleason scores in comparison with carcinomas with low Gleason scores. In DU 145 cell lines with either overexpression or knockdown of PKP3, both imbalances resulted in fewer desmosomal cell contacts. In addition, overexpression of PKP3 in DU 145 cells led to an augmentation in proliferation rate. Our data imply that both loss of PKP1 and up-regulation of PKP3 expression are biologically important events in prostate cancer and are associated with a more aggressive phenotype