Down-regulation of TM4SF is associated with the metastatic potential of gastric carcinoma TM4SF members in gastric carcinoma

<p>Abstract</p> <p>Background</p> <p>The aim of this study was to clarify the clinical significance of TM4SF members CD9, CD63 and CD82 in human gastric carcinoma.</p> <p>Methods</p> <p>By employing RT-PCR and immunohistochemistry, we studied the expression of CD9, CD63 and CD82 in 49 paired tissue specimens of normal gastric mucosa and carcinoma. All tissues were obtained from patients who underwent curative surgery.</p> <p>Results</p> <p>All normal gastric epithelium and gastric ulcer tissues strongly expressed transcripts and proteins of CD9, CD63 and CD82 as compared with corresponding controls. We found a significant correlation between CD63 mRNA level and different pM statuses (P = 0.036). Carcinomas in M0 stage revealed a stronger expression of CD63 than carcinomas in M1 stage. Expression of CD9 protein was found significantly stronger in pN0, pM0 than in advanced pN stages (P = 0.03), pM1 (P = 0.013), respectively. We found the relationship between CD63 expression, gender (p = 0.09) and nodal status (p = 0.028), respectively. Additionally, advanced and metastasized tumor tissues revealed significantly down-regulated CD82 protein expression (p = 0.033 and p = 0, respectively), which correlated with the tumor pTNM stage (p = 0.001).</p> <p>Conclusion</p> <p>The reduction of CD9, CD63 and CD82 expression are indicators for the metastatic potential of gastric carcinoma cells. Unlike their expression in other tumor types, the constitutive expression of CD63 may indicate that this factor does play a direct role in human gastric carcinogenesis.</p

CD98 Increases Renal Epithelial Cell Proliferation by Activating MAPKs

CD98 heavy chain (CD98hc) is a multifunctional transmembrane spanning scaffolding protein whose extracellular domain binds with light chain amino acid transporters (Lats) to form the heterodimeric amino acid transporters (HATs). It also interacts with β1 and β3 integrins by its transmembrane and cytoplasmic domains. This interaction is proposed to be the mechanism whereby CD98 mediates cell survival and growth via currently undefined signaling pathways. In this study, we determined whether the critical function of CD98-dependent amino acid transport also plays a role in cell proliferation and defined the signaling pathways that mediate CD98-dependent proliferation of murine renal inner medullary collecting duct (IMCD) cells. We demonstrate that downregulating CD98hc expression resulted in IMCD cell death. Utilizing overexpression studies of CD98hc mutants that either lacked a cytoplasmic tail or were unable to bind to Lats we showed that CD98 increases serum-dependent cell proliferation by a mechanism that requires the CD98hc cytoplasmic tail. We further demonstrated that CD98-dependent amino acid transport increased renal tubular epithelial cell proliferation by a mechanism that does not require the CD98hc cytoplasmic tail. Both these mechanisms of increased renal tubular epithelial cell proliferation are mediated by Erk and p38 MAPK signaling. Although increased amino transport markedly activated mTor signaling, this pathway did not alter cell proliferation. Thus, these studies demonstrate that in IMCD cells, the cytoplasmic and extracellular domains of CD98hc regulate cell proliferation by distinct mechanisms that are mediated by common MAPK signaling pathways

The CD81 Partner EWI-2wint Inhibits Hepatitis C Virus Entry

Two to three percent of the world's population is chronically infected with hepatitis C virus (HCV) and thus at risk of developing liver cancer. Although precise mechanisms regulating HCV entry into hepatic cells are still unknown, several cell surface proteins have been identified as entry factors for this virus. Among these molecules, the tetraspanin CD81 is essential for HCV entry. Here, we have identified a partner of CD81, EWI-2wint, which is expressed in several cell lines but not in hepatocytes. Ectopic expression of EWI-2wint in a hepatoma cell line susceptible to HCV infection blocked viral entry by inhibiting the interaction between the HCV envelope glycoproteins and CD81. This finding suggests that, in addition to the presence of specific entry factors in the hepatocytes, the lack of a specific inhibitor can contribute to the hepatotropism of HCV. This is the first example of a pathogen gaining entry into host cells that lack a specific inhibitory factor

EWI-2 negatively regulates TGF-β signaling leading to altered melanoma growth and metastasis

In normal melanocytes, TGF-β signaling has a cytostatic effect. However, in primary melanoma cells, TGF-β-induced cytostasis is diminished, thus allowing melanoma growth. Later, a second phase of TGF-β signaling supports melanoma EMT-like changes, invasion and metastasis. In parallel with these “present-absent-present” TGF-β signaling phases, cell surface protein EWI motif-containing protein 2 (EWI-2 or IgSF8) is “absent-present-absent” in melanocytes, primary melanoma, and metastatic melanoma, respectively, suggesting that EWI-2 may serve as a negative regulator of TGF-β signaling. Using melanoma cell lines and melanoma short-term cultures, we performed RNAi and overexpression experiments and found that EWI-2 negatively regulates TGF-β signaling and its downstream events including cytostasis (in vitro and in vivo), EMT-like changes, cell migration, CD271-dependent invasion, and lung metastasis (in vivo). When EWI-2 is present, it associates with cell surface tetraspanin proteins CD9 and CD81 — molecules not previously linked to TGF-β signaling. Indeed, when associated with EWI-2, CD9 and CD81 are sequestered and have no impact on TβR2-TβR1 association or TGF-β signaling. However, when EWI-2 is knocked down, CD9 and CD81 become available to provide critical support for TβR2-TβR1 association, thus markedly elevating TGF-β signaling. Consequently, all of those TGF-β-dependent functions specifically arising due to EWI-2 depletion are reversed by blocking or depleting cell surface tetraspanin proteins CD9 or CD81. These results provide new insights into regulation of TGF-β signaling in melanoma, uncover new roles for tetraspanins CD9 and CD81, and strongly suggest that EWI-2 could serve as a favorable prognosis indicator for melanoma patients

Tetraspanin microdomains in immune cell signalling and malignant disease.

Contains fulltext : 58668.pdf (publisher's version ) (Closed access)A contemporary goal of researchers in leucocyte signalling has been to uncover how cells physically organize and compartmentalize signalling molecules into efficient, regulated signalling networks. This work has revealed important roles of membrane microdomains that are characterized by their distinctive protein and lipid compositions. Recent studies have demonstrated that besides typical cholesterol- and glycosphingolipid-enriched 'rafts', leucocyte membranes are equipped with a different type of microdomain, made up of tetraspanin proteins. Tetraspanin proteins are involved in the organization of tetraspanin-enriched microdomains by virtue of their capacity to specifically associate with key molecules, including integrins, leucocyte receptors and signalling proteins. The aspects of leucocyte function influenced by tetraspanin microdomains include adhesion, proliferation and antigen presentation. However, the mechanisms by which tetraspanin complexes link to intracellular signalling pathways, are still largely unknown. This review discusses how tetraspanin microdomains might function to regulate signalling in lymphoid and myeloid cells, and how they relate to lipid rafts. In addition, we discuss new insights into the role of tetraspanins in malignant disease

Analysis of the gamma-secretase interactome and validation of its association with tetraspanin-enriched microdomains

gamma-Secretase, an aspartyl protease that belongs to the iCLiPs (intramembrane cleaving proteases) family, is a multiprotein complex that consists of presenilin (PS), nicastrin (NCT), Aph-1 and Pen-2 (ref. 1). It is responsible for generation of the beta-amyloid peptide (A beta), the primary component of senile plaques in the brains of patients with Alzheimer's disease. Although the four components are necessary and sufficient for gamma-secretase activity(2-4), additional proteins are possibly involved in its regulation. Consequently, we purified proteins associated with the active gamma-secretase complex from reconstituted PS deficient fibroblasts, using tandem affinity purification (TAP)(5) and identified a series of proteins that transiently interact with the gamma-secretase complex and are probably involved in complex maturation, membrane trafficking and, importantly, the tetraspanin web. Tetraspanins form detergent-resistant microdomains in the cell membrane and regulate cell adhesion, cell signalling and proteolysis(6,7). Association of the gamma-secretase complex with tetraspanin-enriched microdomains provides an explanation for the previously documented localization of gamma-secretase to raft-like domains(8). Thus, these studies suggest that maintenance of the integrity of tetraspanin microdomains contributes to the refinement of proteolytic activity of the gamma-secretase complex