Dispensable role of protein 4.1B/DAL-1 in rodent adrenal medulla regarding generation of pheochromocytoma and plasmalemmal localization of TSLC1

Immunohistochemical study of the membrane skeletal protein, membrane protein palmitoylated 6 (MPP6), in the mouse small intestine

The membrane protein palmitoylated (MPP) family belongs to the membrane-associated guanylate kinase (MAGUK) family. MPP1 interacts with the protein 4.1 family member, 4.1R, as a membrane skeletal protein complex in erythrocytes. We previously described the interaction of another MPP family, MPP6, with 4.1G in the mouse peripheral nervous system. In the present study, the immunolocalization of MPP6 in the mouse small intestine was examined and compared with that of E-cadherin, zonula occludens (ZO)-1, and 4.1B, which we previously investigated in intestinal epithelial cells. The immunolocalization of MPP6 was also assessed in the small intestines of 4.1B-deficient (-/-) mice. In the small intestine, Western blotting revealed that the molecular weight of MPP6 was approximately 55-kDa, and MPP6 was immunostained under the cell membranes in the basolateral portions of almost all epithelial cells from the crypts to the villi. The immunostaining pattern of MPP6 in epithelial cells was similar to that of E-cadherin, but differed from that of ZO-1. In intestinal epithelial cells, the immunostained area of MPP6 was slightly different from that of 4.1B, which was restricted to the intestinal villi. The immunolocalization of MPP6 in small intestinal epithelial cells was similar between 4.1B(-/-) mice and 4.1B(+/+) mice. In the immunoprecipitation study, another MAGUK family protein, calcium/calmodulin-dependent serine protein kinase (CASK), was shown to molecularly interact with MPP6. Thus, we herein showed the immunolocalization and interaction proteins of MPP6 in the mouse small intestine, and also that 4.1B in epithelial cells was not essential for the sorting of MPP6.

DAL-1 attenuates epithelial-to mesenchymal transition in lung cancer

BACKGROUND

Epithelial-to mesenchymal transition (EMT) involves in metastasis, causing loss of epithelial polarity. Metastasis is the major cause of carcinoma-induced death, but mechanisms are poorly understood. Here we identify differentially expressed in adenocarcinoma of the lung-1 (DAL-1), a protein belongs to the membrane-associated cytoskeleton protein 4.1 family, as an efficient suppressor of EMT in lung cancer.

METHODS

The relationship between DAL-1 and EMT markers were analyzed by using immunohistochemistry in the clinical lung cancer tissues. Quantitative real-time PCR and western blot were used to characterize the expression of the EMT indicator mRNAs and proteins in DAL-1 overexpressed or knockdown cells. DAL-1 combined proteins were assessed by co-immunoprecipitation.

RESULTS

DAL-1 levels were strongly reduced even lost in lymph node metastasis and advanced pathological stage of human lung carcinomas. Overexpression of DAL-1 altered the expression of numerous EMT markers, such as E-cadherin, β-catenin Vimentin and N-cadherin expression, meanwhile changed the morphological shape of lung cancer cells, and whereas silencing DAL-1 had an opposite effect. DAL-1 directly combined with E-cadherin promoter and regulated its expression that could be the reason for impairing EMT and decreasing cell migration and invasion. Strikingly, HSPA5 was found as DAL-1 direct binding protein.

CONCLUSIONS

These results suggest that tumor suppressor DAL-1 could also attenuate EMT and be important for tumor metastasis in the early transformation process in lung cancer.

Overexpression of tumor suppressor TSLC1 by a survivin-regulated oncolytic adenovirus significantly inhibits hepatocellular carcinoma growth

PURPOSE

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors worldwide. Oncolytic viruses represent a promising therapeutic agent or vehicle to human cancers due to their ability of selectively lysing cancer cells but not in normal cells. TSLC1, a novel tumor suppressor gene, was loss in many human cancers including HCC, not in normal cells. The current study is focused on the antitumor effect of TSLC1-armed survivin-regulated oncolytic adenovirus for HCC and to explore their molecular mechanism.

METHODS

The expression of tumor suppressor TSLC1 and survivin was detected by quantitative PCR. The recombinant virus Ad.SP-E1A-E1B((Δ55))-TSLC1 (brief name as SD55-TSLC1) was constructed by inserting TSLC1 gene into the dual-regulated oncolytic adenovirus vector Ad.SP-E1A-E1B((Δ55)). Then, we performed the antitumor experiments of SD55-TSLC1 in vitro and in nude mice xenografted with Huh7 liver cancer.

RESULTS

The expression of TSLC1 was lower in HCC cells than in normal cells, which implied TSLC1 is a tumor suppressor of liver cancer. Survivin expression is higher in detected HCC cells than in normal cells. The SD55-TSLC1 exhibited an excellent antitumor effect on HCC cell growth in vitro but does no or little damage to normal liver cells. Animal experiment further confirmed that SD55-TSLC1 achieved significant inhibition of Huh7 liver cancer xenografted growth. Furthermore, the mechanism of antitumor efficacy by SD55-TSLC1 was elucidated to be due to the activation of caspase apoptotic pathway including the inducement of caspase-3, caspase-8, and poly (ADP-ribose) polymerase cleavage. This is the first report of TSLC1 by oncolytic adenovirus with an excellent antitumor effect to liver cancer growth.

CONCLUSION

These data suggest that an oncolytic adenovirus expressing TSLC1 is effective and support that SD55-TSLC1 may be a potent antitumoral agent for future clinical trials of liver cancer.

Essential function of protein 4.1G in targeting of membrane protein palmitoylated 6 into Schmidt-Lanterman incisures in myelinated nerves

Protein 4.1G is a membrane skeletal protein found in specific subcellular structures in myelinated Schwann cells and seminiferous tubules. Here, we show that in the mouse sciatic nerve, protein 4.1G colocalized at Schmidt-Lanterman incisures (SLI) and the paranodes with a member of the membrane-associated guanylate kinase (MAGUK) family, membrane protein palmitoylated 6 (MPP6). Coimmunoprecipitation experiments revealed that MPP6 was interacting with protein 4.1G. In contrast to wild-type nerves, in 4.1G knockout mice, MPP6 was found largely in the cytoplasm near Schwann cell nuclei, indicating an abnormal protein transport. Although the SLI remained in the 4.1G knockout sciatic nerves, as confirmed by E-cadherin immunostaining, their shape was altered in aged 4.1G knockout nerves compared to their shape in wild-type nerves. In the seminiferous tubules, MPP6 was localized similarly to protein 4.1G along cell membranes of the spermatogonium and early spermatocytes. However, in contrast to myelinated peripheral nerves, the specific localization of MPP6 in the seminiferous tubules was unaltered in the absence of protein 4.1G. These results indicate that 4.1G has a specific role in the targeting of MPP6 to the SLI and the assembly of these subcellular structures.

Construction of eukaryotic expression vector of TSLC1 gene

INTRODUCTION

To construct a eukaryotic expression vector of the tumour suppressor in lung cancer 1 (TSLC1) gene, so as to explore the mechanisms of tumour suppression of the gene theoretically.

MATERIAL AND METHODS

The open reading frame (ORF) of TSLC1 gene was amplified with RT-PCR from normal human foreskin acrobystia, and cloned to pMD19-T simple vector (TA Clone method). The resultant plasmid was transformed into Escherichia coli JM109 for amplification. The TA Clone recombinant was digested by double restriction enzyme (Bgl II/EcoR I) and analysed with agarose gel electrophoresis. The positive one was sequenced. The inserted DNA fragment was recovered, and then it was mounted into the eukaryotic expression vector pIRES2-EGFP, transformed into E. coli JM109 for amplification. A positive recombinant plasmid named pIRES2-EGFP-TSLC1 was confirmed by Bgl II/EcoR I double-enzyme digestion analysis.

RESULTS

RT-PCR amplified the ORF of the TSLC1 gene. It was approximately 1400 base pairs. The obtained DNA was confirmed a high degree of homology with the sequence of TSLC1 cDNA sequence (AY358334) stored at GenBank.

CONCLUSIONS

Construction of a TSLC1 eukaryotic expression vector was successful, and it has established a solid foundation for further study.

Involvement of a membrane skeletal protein, 4.1G, for Sertoli/germ cell interaction

We previously reported that a membrane skeletal protein, 4.1G (also known as EPB41L2), is immunolocalized in mouse seminiferous tubules. In this study, the 4.1G immunolocalizaiton was precisely evaluated at various stages of the mouse seminiferous epithelial cycle with ‘in vivocryotechnique’ and also with pre-embedding immunoelectron microscopy in testicular tissues whose ultrastructures were well preserved with glycerol treatment before cryosectioning. In addition, 4.1G-deficient mice were produced, and the morphology of their seminiferous tubules was also evaluated. The 4.1G immunolocalization was different among stages, indicating that it was not only along cell membranes of Sertoli cells, but also those of spermatogonia and early spermatocytes. To confirm the 4.1G immunolocalization in germ cells,in vitroculture of spermatogonial stem cells (SSCs) was used for immunocytochemistry and immunoblotting analysis. In the cultured SSCs, 4.1G was clearly expressed and immunolocalized along cell membranes, especially at mutual attaching regions. In testicular tissues, cell adhesion molecule-1 (CADM1), an intramembranous adhesion molecule, was colocalized on basal parts of the seminiferous tubules and immunoprecipitated with 4.1G in the tissue lysate. Interestingly, in the 4.1G-deficient mice, histological manifestation of the seminiferous tubules was not different from that in wild-type mice, and the CADM1 was also immunolocalized in the same pattern as that in the wild-type. Moreover, the 4.1G-deficient male mice were fertile. These results were probably due to functional redundancy of unknown membrane skeletal molecules in germ cells. Thus, a novel membrane skeletal protein, 4.1G, was found in germ cells, and considering its interaction with CADM family, it probably has roles in attachment of both Sertoli–germ and germ–germ cells.