Characterization of tree shrew telomeres and telomerase

The use of tree shrews as experimental animals for biomedical research is a new practice. Several recent studies suggest that tree shrews are suitable for studying cancers, including breast cancer, glioblastoma, lung cancer, and hepatocellular carcinoma. However, the telomeres and the telomerase of tree shrews have not been studied to date. Here, we characterize telomeres and telomerase in tree shrews. The telomere length of tree shrews is approximately 23 kb, which is longer than that of primates and shorter than that of mice, and it is extended in breast tumor tissues according to Southern blot and flow-fluorescence in situ hybridization analyses. Tree shrew spleen, bone marrow, testis, ovary, and uterus show high telomerase activities, which are increased in breast tumor tissues by telomeric repeat amplification protocol assays. The telomere length becomes shorter, and telomerase activity decreases with age. The tree shrew TERT and TERC are more highly similar to primates than to rodents. These findings lay a solid foundation for using tree shrews to study aging and cancers.

The Tree Shrew as a Model for Cancer Research

Animal disease models are necessary in medical research, and an appropriate animal model is of great importance for studies about the prevention or treatment of cancer. The most important thing in the selection of animal models is to consider the similarity between animals and humans. The tree shrew (Tupaia belangeri) is a squirrel-like mammal which placed in the order Scandentia. Whole-genome sequencing has revealed that tree shrews are extremely similar to primate and humans than to rodents, with many highly conserved genes, which makes the data from studies that use tree shrews as models more convincing and the research outcomes more easily translatable. In tumor research, tree shrews are often used as animal models for hepatic and mammary cancers. As research has progressed, other types of tree shrew tumor models have been developed and exhibit clinical manifestations similar to those of humans. Combining the advantages of both rodents and primates, the tree shrew is expected to be the most powerful animal model for studying tumors.

Characterization and phylogenetic analysis of Krüppel-like transcription factor (KLF) gene family in tree shrews (Tupaia belangeri chinensis)

Krüppel-like factors (KLFs) are a family of zinc finger transcription factors regulating embryonic development and diseases. The phylogenetics of KLFs has not been studied in tree shrews, an animal lineage with a closer relationship to primates than rodents. Here, we identified 17 KLFs from Chinese tree shrew (Tupaia belangeri chinensis). KLF proteins are highly conserved among humans, monkeys, rats, mice and tree shrews compared to zebrafish and chickens. The CtBP binding site, Sin3A binding site and nuclear localization signals are largely conserved between tree shrews and human beings. Tupaia belangeri (Tb) KLF5 contains several conserved post-transcriptional modification motifs. Moreover, the mRNA and protein expression patterns of multiple tbKLFs are tissue-specific. TbKLF5, like hKLF5, significantly promotes NIH3T3 cell proliferation in vitro. These results provide insight for future studies regarding the structure and function of the tbKLF gene family.

Identification of the immunogenic domains in HBsAg preS1 region using overlapping preS1 fragment fusion proteins

AIM: The incorporation of hepatitis B virus (HBV) preS1 region into epitope-based vaccines against HBV has been accepted widely, but the incorporate site and size of preS1 sequence is controversial. Therefore our purpose was to further investigate its immunogenic domains for the epitope-based hepatitis B vaccine design.

METHODS: Eight GST fusion proteins containing overlapping preS1 fragments in preS1 (21-119) region were expressed in E.coli. Using these purified fusion proteins, the immunogenic domains in preS1 region were identified in detail in mice and humans by Western blot analysis and ELISA.

RESULTS: The results in mice showed that the immu-nogenic domains mainly existed in preS1 (21-59) and preS1 (95-109). Similarly, these fragments had strong immunogenicity in humans; whereas the other parts except for preS1 (60-70) also had some immunogenicity. More importantly, a major immunogenic domain, preS1 (34-59), which has much stronger immunogenicity, was identified. Additionally, the antibodies against some preS1 fragments, especially preS1 (34-59), were speculated to be virus-neutralizing.

CONCLUSION: Eight GST fusion proteins containing overlapping preS1 fragments were prepared successfully. They were used for the study on the immunogenic dom-ains in preS1 (21-119) region. The preS1 (34-59) fragm-ents were the major immunogenic domains in the preS1 region, and the antibodies against these fragments were speculated to be virus-neutralizing. Therefore, the incorporation of preS1 (34-59) fragments into epitope-based HBV vaccines may be efficient for enhancement of immune response. Additionally, the results also imply that there are more complex immune responses to preS1 region and more abundant immunogenic domains in humans.

DNA polymerase ζ: new insight into eukaryotic mutagenesis and mammalian embryonic development

Information about the mechanisms that generate mutations in eukaryotes is likely to be useful for understanding human health concerns, such as genotoxicity and cancer. Eukaryotic mutagenesis is largely the outcome of attacks by endogenous and environmental agents. Except for DNA repair, cell cycle checkpoints and DNA damage avoidance, cells have also evolved DNA damage tolerance mechanism, by which lesion-targeted mutation might occur in the genome during replication by specific DNA polymerases to bypass the lesions (translesion DNA synthesis, TLS), or mutation on undamaged DNA templates (untargeted mutation) might be induced. DNA polymerase ζ (pol ζ), which was found firstly in budding yeast Saccharomyces cerevisiae and consists of catalytic subunit scRev3 and stimulating subunit scRev7, has received more attention in recent years. Pol ζ is a member of DNA polymerase δ subfamily, which belongs to DNA polymerase B family, and exists in almost all eukaryotes. Human homolog of the scRev3 gene is located in chromosome region 6q21, and the mouse equivalent maps to chromosome 10, distal to the c-myb gene and close to the Macs gene. Alternative splicing, upstream out-of frame ATG can be found in yeast scRev3, mouse and human homologs. Furthermore, the sequence from 253-323 immediate upstream of the AUG initiator codon has the potential to form a stem-loop hairpin secondary structure in REV3 mRNA, suggesting that human REV3 protein may be expressed at low levels in human cells under normal growth conditions. The functional domain analysis showed that yeast Rev3-980 tyrosine in conserved region II is at the polymerase active site. Human REV3 amino acid residues 1776-2195 provide a REV7 binding domain, and REV7 amino acid residues 1-211 provide a bind domain for REV1, REV3 and REV7 itself. More interestingly, REV7 interacts with hMAD2 and therefore might function in the cell cycle control by affecting the activation of APC (anaphase promoting complex). Currently it has been known that pol ζ is involved in most spontaneous mutation, lesion-targeted mutation via TLS, chemical carcinogen induced untargeted mutation and somatic hypermutation of antibody genes in mammalian. In TLS pathway, pol ζ acts as a "mismatch extender" with combination of other DNA polymerases, such as pol ι. Unlike in yeast, it was found that pol ζ also functioned in mouse embryonic development more recently. It was hypothesized that the roles of pol ζ in TLS and cell cycle control might contribute to mouse embryonic lethality.

Response of human REV3 gene to gastric cancer inducing carcinogen N-methyl-N’-nitro-N-nitrosoguanidine and its role in mutagenesis

AIM: To understand the response of human REV3 gene to gastric cancer inducing carcinogen N-methyl-N’-nitro-N-nitrosoguanidine (MNNG) and its role in human mutagenesis.

METHODS: The response of the human REV3 gene to MNNG was measured in human 293 cells and FL cells by RT-PCR. By using antisense technology, mutation analysis at HPRT locus (on which lesion-targeted mutation usually occurs) was conducted in human transgenic cell line FL-REV3^- by 8-azaguanine screening, and mutation occurred on undamaged DNA template was detected by using a shuttle plasmid pZ189 as the probe in human transgenic cell lines 293-REV3^- and FL-REV3^-. The blockage effect of REV3 was measured by combination of reverse transcription-polymerase chain reaction to detect the expression of antisense REV3 RNA and Western blotting to detect the REV3 protein level.

RESULTS: The human REV3 gene was significantly activated by MNNG treatment, as indicated by the upregulation of REV3 gene expression at the transcriptional level in MNNG-treated human cells, with significant increase of REV3 expression level by 0.38 fold, 0.33 fold and 0.27 fold respectively at 6 h, 12 h and 24 h in MNNG-treated 293 cells (P < 0.05); and to 0.77 fold and 0.65 fold at 12 h and 24 h respectively in MNNG-treated FL cells (P < 0.05). In transgenic cell line (in which REV3 was blocked by antisense REV3 RNA), high level of antisense REV3 RNA was detected, with a decreased level of REV3 protein. MNNG treatment significantly increased the mutation frequencies on undamaged DNA template (untargeted mutation), and also at HPRT locus (lesion-targeted mutation). However, when REV3 gene was blocked by antisense REV3 RNA, the MNNG-induced mutation frequency on undamaged DNA templates was significantly decreased by 3.8 fold (P < 0.05) and 5.8 fold (P < 0.01) respectively both in MNNG-pretreated transgenic 293 cells and FL cells in which REV3 was blocked by antisense RNA, and almost recovered to their spontaneous mutation levels. The spontaneous HPRT mutation was disappeared in REV3-disrupted cells, and induced mutation frequency at HPRT locus significantly decreased from 8.66 × 10^-6 in FL cells to 0.14 × 10^-6 in transgenic cells as well (P < 0.01).

CONCLUSION: The expression of the human REV3 can be upregulated at the transcriptional level in response to MNNG. The human REV3 gene plays a role not only in lesion-targeted DNA mutagenesis, but also in mutagenesis on undamaged DNA templates that is called untargeted mutation.

Signal transduction of gap junctional genes, connexin32, connexin43 in human hepatocarcinogenesis

AIM: To investigate gap junctional intercellular communication (GJIC) in hepatocellular carcinoma cell lines, and signal transduction mechanism of gap junction genes connexin32(CX32), connexin43(CX43) in human hepatocarcinogenesis.

METHODS: Scarped loading and dye transfer (SLDT) was employed with Lucifer Yellow (LY) to detect GJIC function in hepatocellular carcinoma cell lines HHCC, SMMC-7721 and normal control liver cell line QZG. After Fluo-3AM loading, laser scanning confocal microscope (LSCM) was used to measure concentrations of intracellular calcium [Ca²⁺]i in the cells. The phosphorylation on tyrosine of connexin proteins was examined by immunoblot.

RESULTS: SLDT showed that ability of GJIC function was higher in QZG cell than that in HHCC and SMMC-7721 cell lines. By laser scanning confocal microscopy, concentrations of intracellular free calcium [Ca²⁺]i was much higher in QZG cell line (108.37 nmol/L) than those in HHCC (35.13 nmol/L) and SMMC-7721 (47.08 nmol/L) cells. Western blot suggested that only QZG cells had unphosphorylated tyrosine in CX32 protein of 32 ku and CX43 protein of 43 ku; SMMC-7721 cells showed phosphorylated tyrosine CX43 protein.

CONCLUSION: The results indicated that carcinogenesis and development of human hepatocellular carcinoma related with the abnormal expression of CX genes and disorder of its signal transduction pathway, such as decrease of [Ca²⁺]i, post-translation phosphorylation on tyrosine of CX proteins which led to a dramatic disruption of GJIC.

Expression of RNase H of human hepatitis B virus polymerase in Escherichia coli

AIM: To amplify HBV-RNase H gene fragment and expression of RNase H for further use in the studies of HBV associated liver diseases.

METHODS: The encoding gene of HBV-RNase H was separately amplified for the first half and second half (H1 and H2) by PCR from full length HBV gene and cloned into pT7Blue-T vector. Clones were first screened by digestion with Xba I and Hind III enzyme for the correct size, and analyzed further by DNA sequencing. The RNase H1 and H2 fragments isolated from XbaI and Hind III digestion products of pT7 Blue-RNase H plasmid were ligated to the GSTag expressing vectors separately, and expressed in E.coli BL21. The expressed proteins were checked by PAGE gel and Western blot.

RESULTS: Both H1 and H2 nucleotide seqences consisting of known genes and proteins, in correct size, were further confirmed by Western blot to be the GST and RNase H1 or H2 fusion proteins.

CONCLUSION: The successful cloning and expression of HBV-RNase H will contribute to further research and application in HBV-associated diseases.

The analysis of γ-glutamyl transpeptidase gene in different type liver tissues

AIM: To probe the value of γ-glutamyl transpeptidase (GGT) messenger RNA in monitoring canceration of liver cells and for early diagnosis of hepatocellular carcinoma (HCC), by researching the types of GGT messenger RNA (GGTmRNA) in liver tissues and peripheral blood of different hepatopathy.

METHODS: The three types of GGTmRNA (A, B, C) in liver tissues and peripheral blood from the patients with HCC, noncancerous hepatopathy, hepatic benign tumor, secondary carcinoma of liver, and healthy persons were detected by reverse-transcription polymerase chain reaction (RT-PCR).

RESULTS: (1) In normal liver tissues, type A was predominantly found (100.00%), type B was not found, type C was found occasionally (25.00%); (2) The distribution of types of GGTmRNA in liver tissues with acute hepatitis, chronic hepatitis, cirrhosis, alcoholic hepatopathy was similar as in normal liver tissues (P > 0.05), but type B was found in 3 of 18 patients with chronic hepatitis (16.67%), and also in 3 of 11 patients with cirrhosis (27.27%); (3) There was no significant difference of types of GGTmRNA between liver tissues with hepatic benign tumor, secondary carcinoma of liver and normal liver tissues (P > 0.05); (4) Type B was predominant in cancerous tissues with HCC (87.5%), the prevalence of type B in cancerous tissues was significantly higher than that in normal liver tissues (0/12) (P < 0.05), but the prevalence of type A in cancerous tissues (46.88%) was significantly lower than that in normal liver tissues (100.00%) (P < 0.05), and the prevalence of type C (6.25%) in cancerous was the same as that in normal liver tissues (25.00%) (P > 0.05). In noncancerous tissues of livers with HCC, the main types were type A and type B, the prevalence of type A (85.71%, 90.48%) and type C (14.29%, 9.52%) in noncancerous tissues of liver with HCC was similar as that in normal liver tissues (A: 100.00%; C: 25.00%) (P > 0.05), but the prevalence of type B (80.95%, 76.19%) in noncancerous tissues of livers with HCC was significantly higher than that in normal liver tissues (0/12) (P < 0.05); (5) The prevalence of type B (37.5%) in peripheral blood with HCC was higher than that in normal person (0/12) (P < 0.05). In peripheral blood, type B was found in 4 of 11 cases of HCC with serum AFP negative.

CONCLUSION: The shift of types of GGTmRNA from A to B in liver tissues may be closely related to the development of HCC, and the analysis of GGT gene may provide a useful tool for early diagnosis of HCC.

Construction and characterization of an experimental ISCOMS-based hepatitis B polypeptide vaccine

AIM: To characterize the biochemical and immunological properties of an experimental ISCOMS vaccine prepared from a novel therapeutic polypeptide based on T cell epitopes of HBsAg, and a heptatis B-ISCOMS was prepared and investigated.

METHODS: An immunostimulating complexes (ISCOMS)-based vaccine containing a novel therapeutic hepatits B polypeptide was prepared by dialysis method, and its formation was visualized by electron microscopy and biochemically verified by SDS-polyacrylamide gel electrophoresis. Amount of the peptide within ISCOMS was determined by Bradford assay, and specific CTL response was detected by ELISPOT assay.

RESULTS: Typical cage-like structures of submicroparticle with a diameter of about 40 nm were observed by electron microscopy. Results from Bradford assay showed that the level of peptide incorporation was about 0.33 g•L⁻¹. At the paralleled position close to the sixth band of the molecular weight marker (3480 kDa) a clear band was shown in SDS-PAGE analysis, indicating successful incorporation of polypeptide into ISCOMS. It is suggested that ISCOMS delivery system could efficiently improve the immunogenicity of polypeptide and elicit specific immune responses in vivo by the results of ELISPOT assay, which showed that IFN-γ producing cells (specific CTL responses) were increased (spots of ISCOMS-treated group: 47 ± 5, n = 3; control group: 5 ± 2, n = 3).

CONCLUSION: ISCOMS-based hepatitis B polypeptide vaccine is successfully constructed and it induces a higher CTL response compared with short polypeptides vaccine in vivo.

Expression of gap junction genes connexin 32 and connexin 43 mRNAs and proteins, and their role in hepatocarcinogenesis

AIM: To investigate the relationship between hepatocarcinogenesis and the expression of connexin32 (cx32), connexin43 (cx43) mRNAs and proteins in vitro.

METHODS: Gap junction genes cx32 and cx43 mRNA in hepatocellular carcinoma cell lines HHCC, SMMC-7721 and normal liver cell line QZG were detected by in situ hybridization (ISH) with digoxin-labeled cx32, and cx43 cDNA probes. Expression of Cx32 and Cx43 proteins in the cell lines was revealed by indirect immuno-fluorescence and flow cytometry (FCM).

RESULTS: Blue positive hybridization signals of cx32 and cx43 mRNAs detected by ISH with cx32 and cx43 cDNA probes respectively were located in cytoplasm of cells of HHCC, SMMC-7721 and QZG. No significant difference of either cx32 mRNA or cx43 mRNA was tested among HHCC, SMMC-7721 and QZG (P = 2.673, HHCC vs QZG; P = 1.375, SMMC-7721 vs QZG). FCM assay showed that the positive rates of Cx32 protein in HHCC, SMMC-7721 and QZG were 0.7%, 1.7% and 99.0%, and the positive rates of Cx43 protein in HHCC, SMMC-7721 and QZG were 7.3%, 26.5% and 99.1% respectively. Significant differences of both Cx32 and Cx43 protein expression existed between hepatocellular carcinoma cell lines and normal liver cell line (P = 0.0069, HHCC vs QZG; P = 0.0087, SMMC-7721 vs QZG). Moreover, the fluorescent intensities of Cx32 and Cx43 proteins in HHCC, SMMC-7721 were lower than that in QZG.

CONCLUSION: Hepatocellular carcinoma cell lines HHCC and SMMC-7721 exhibited lower positive rates and fluorescent intensities of Cx32, Cx43 proteins compared with that of normal liver cell line QZG. It is suggested that lower expression of both Cx32 and Cx43 proteins in hepatocellular carcinoma cells could play pivotal roles in the hepatocarcinogenesis. Besides, genetic defects of cx32 and cx43 in post-translational processing should be considered.