Expression of vascular endothelial growth factor in human gastric carcinomas

Vascular endothelial growth factor (VEGF), also known as vascular permeability factor, is a secreted protein which may play a pivotal role in tumor-associated microvascular angiogenesis and hyperpermeability. The expression of mRNA for VEGF was examined in eight gastric carcinoma cell lines and 30 gastric carcinoma tissues as well as corresponding normal mucosa. All the cell lines expressed VEGF mRNA at various levels that correlated well with the amounts of VEGF secreted into the condition medium. The expression of VEGF mRNA by TMK-1 cells was increased by the treatment of epidermal growth factor (EGF) or interleukin-1alpha (IL-1alpha), whereas it was decreased by the treatment of interferon-beta (IFN-beta). In gastric carcinoma tissues, the level of VEGF mRNA in primary tumors was higher than that in the corresponding normal mucosas in six (46%) of 13 well-differentiated adenocarcinomas and in two (12%) of 17 poorly differentiated adenocarcinomas, respectively. Vessel counts in well-differentiated adenocarcinomas had a tendency to be higher than those in poorly differentiated adenocarcinomas. In well-differentiated adenocarcinomas, the levels of VEGF mRNA expression tended to be higher in carcinomas of advanced stage than in early stage carcinomas. Both in situ mRNA hybridization and immunohistochemistry demonstrated the presence of VEGF expression within the tumor cells. These results suggest that VEGF may confer angiogenesis and progression of human gastric carcinomas, especially of the well-differentiated type.     

Telomerase activity in human development is regulated by human telomerase reverse transcriptase (hTERT) transcription and by alternate splicing of hTERT transcripts

Short mobile elements are present in different recombined forms as interspersed GC-rich islands between AT rich centromeric 155 bp tandem repeats in the dipteran Chironomus pallidivittatus . The basic element is 80 bp long, has a pronounced invert repeat structure and contains a 17 bp segment similar to the CENP-B box in mammals. The element inserts into a specific site of the 155 bp repeat in a defined orientation surrounded by 2 bp direct repeats. The total number per genome of the main variant is <20. Elements can be present in all centromeres from C.pallidivittatus and the sibling species Chironomus tentans with pronounced differences in distribution within and between species.     

Expression of telomerase activity in human chorion

Telomerase activation is required for cellular immortalization and is found in most malignant tumors. Normal somatic cells are generally telomerase-negative, except for stem cells in renewing tissues. During pregnancy, human trophoblast continues to proliferate and acts as proliferating stem cells for the development of chorion and the formation of placenta. In the present study, a total of 105 chorions from placentas at various weeks of gestation were examined for telomerase activity using the telomeric repeat amplification protocol (TRAP) assay. Twenty-five of 33 (76%) normal early chorions at 5 to 9 weeks gestation were telomerase-positive. Chorions from early spontaneous abortions also exhibited telomerase activity but at a low level. In contrast, only 2 (4%) late chorions at 34 to 41 weeks gestation expressed telomerase activity. Significant telomerase activity was observed in trophoblast cell fractions of chorion, demonstrating trophoblast to be the source of the activity. Expression of human telomerase catalytic subunit (hTRT) was observed in early chorions, but not in late placenta, and there was a close correlation between telomerase activity and hTRT expression. In contrast, expression of human telomerase RNA component (hTR) was observed in both early and late chorions and was not liked to telomerase activity. These findings suggest that telomerase activity in chorion is critically regulated over the course of gestation, associated with hTRT expression. The findings of the present study also appear to support the emerging concept that normal somatic cells with stem cell-like characteristics can express telomerase activity.     

Expression of amphiregulin, a novel gene of the epidermal growth factor family, in human gastric carcinomas

The expression of mRNA for amphiregulin (AR), a novel gene of the epidermal growth factor family, was examined in 8 human gastric carcinoma cell lines and 32 gastric carcinoma tissues as well as corresponding normal mucosa. Of the 8 gastric carcinoma cell lines, 7 expressed 1.4 kb AR mRNA at various levels. The expression of AR mRNA by TMK-1 and MKN-28 cells was increased by treatment with epidermal growth factor or transforming growth factor a. In surgical cases, all the gastric carcinoma tissues and their adjacent normal mucosa expressed AR mRNA. Interestingly, 20 (62.5%) out of 32 tumors expressed AR mRNA at higher levels than their corresponding normal mucosas (tumor/normal > or = 1.2). No obvious correlation was observed between the AR mRNA levels and the histological types or tumor staging of gastric carcinoma. Immunohistochemically, AR protein was localized to the cytoplasm and/or nucleus in tumor cells. These results suggest that AR produced by tumor cells may be involved in the pathogenesis and/or progression of human gastric carcinoma.     

Expression profile of the putative catalytic subunit of the telomerase gene

Telomerase, a ribonucleoprotein complex, adds hexameric repeats called telomeres to the growing ends of chromosomal DNA. The enzyme telomerase activity is present in a vast majority of tumors but is repressed in most normal tissues. Recently, two groups have reported the molecular cloning of the putative catalytic subunit (hEST2/hTRT) of the telomerase gene. We investigated the expression of this gene in diverse tumor-derived cell lines and tumors as well as in various normal tissues. The expression of hEST2/hTRT was detectable in tumor-derived cell lines, primary breast tumors, pancreatic tumors, and kidney tumors. Furthermore, the expression of hEST2/hTRT was down-regulated in response to a differentiation inducer. However, several normal tissues also expressed varying levels of hEST2/hTRT. Early passage cultures of endothelial fibroblasts and some epithelial cells also expressed the telomerase gene, albeit at low levels. In contrast, the expression of TLP1/TP1, the human homologue of Tetrahymena p80 telomerase subunit, was similar in all of these samples. Our results indicate that the differences in expression of hEST2/hTRT in tumor versus normal cells are relative and are not absolute.     

The catalytic subunit of yeast telomerase

Telomerase is an RNA-directed DNA polymerase, composed of RNA and protein subunits, that replicates the telomere ends of linear eukaryotic chromosomes. Using a genetic strategy described here, we identify the product of the EST2 gene, Est2p, as a subunit of telomerase in the yeast Saccharomyces cerevisiae. Est2p is required for enzyme catalysis, as mutations in EST2 were found to result in the absence of telomerase activity. Immunochemical experiments show that Est2p is an integral subunit of the telomerase enzyme. Critical catalytic residues present in RNA-directed DNA polymerases are conserved in Est2p; mutation of one such residue abolishes telomerase activity, suggesting a direct catalytic role for Est2p.