QSG-7701 human hepatocytes form polarized acini in three-dimensional culture.

Hepatocytes are polarized and fulfill a variety of liver-specific functions in vivo; but the polarized tissue structure and many of these functions are lost when the cells are cultured on plastic. To recapitulate the polarized structure and tissue-specific function of liver cells in culture, we established a three-dimensional (3D) culture assay with the human hepatocyte line QSG-7701. In 3D Matrigel culture, QSG-7701 cells formed polarized spheroids with a center lumen, which is reminiscent of bile canaliculi in the liver. Immunofluoresence analysis showed that F-actin bundles and radixin were mainly located at the apical membrane and that alpha6 and beta1 integrins were localized basally in 3D culture. Lumen formation was associated with the selective apoptosis of centrally located cells and was accompanied by proliferative suppression during acinar development. Compared to QSG-7701 cells in 2D or agarose gel cultures, the cells in 3D Matrigel culture maintained a given direction of biliary excretion and acquired higher levels of cytochrome P450 and albumin expression. Our study shows that the immortal human hepatocytes, QSG-7701, in 3D Matrigel culture reacquire cardinal features of glandular epithelium in vivo, providing an ex vivo model to study liver-specific function and tumorigenesis.

[Preparation of a novel telomerase inhibitory protein LPTS-L].

The gene for LPTS is originally cloned as a human liver-related putative tumor suppressor (LPTS) gene that encodes a full length protein of 328 amino acids (LPTS-L). LPTS-L is also identified as a telomerase inhibitor to regulate telomere length in the cells. To facilitate the functional and structural studies of LPTS-L protein, the cDNA for LPTS-L was cloned into the expression vector pET-24 in frame to generate a recombinant plasmid pET-24-LPTS. The LPTS-L protein was expressed in E. coli BL21 solublely, and purified by Ni Sepharose affinity chromatography which, however, is not fit for large scale protein purification. The gene of LITS-L was then PCR amplified to remove the 6 x His tag, and cloned into pET-24a. The non-fusion protein of LPTS-L was expressed in E. coli B21, and purified by phosphocellulose P11 chromatography. The purity of LPTS-L protein was about 55% after that procedure,and arrived at 80% after second purification by Sephadex G-100 chromatography. Western Blotting analysis showed that the band reflects the specific binding of anti-LPTS antiserum against the purified LPTS-L protein. The TRAP assay was performed to detect the telomerase inhibitory activity of LPTS-L protein in vitro. It was observed that the purified LPTS-L inhibited the activity of telomerase greatly, similarly with that of LPTS-L protein purified by Ni Sepharose 4B. Our results suggest that phosphocellulose P11 plus Sephadex G-100 chromatography could substitute for Ni Sepharose 4B affinity chromatography for preparation of purified LPTS-L protein. Through this study, a technique for preparation of LPTS-L protein in a large scale is established.

Genes encoding Pir51, Beclin 1, RbAp48 and aldolase b are up or down-regulated in human primary hepatocellular carcinoma.

AIM: To reveal new tumor markers and target genes from differentially expressed genes of primary tumor samples using cDNA microarray. METHODS: The (33 )P labeled cDNAs were synthesized by reverse transcription of message RNA from the liver cancerous tissue and adjacent non-cancerous liver tissue from the same patient and used to hybridize to LifeGrid 1.0 cDNA microarray blot containing 8400 known and unique human cDNA gene targets, and an expression profile of genes was produced in one paired human liver tumor tissue. After a global analysis of gene expression of 8400 genes, we selected some genes to confirm the differential expression using Northern blot and RT-PCR. RESULTS: Parallel analysis of the hybridized signals enabled us to get an expression profile of genes in which about 500 genes were differentially expressed in the paired liver tumor tissues. We identified 4 genes, the expression of three (Beclin 1, RbAp48 and Pir51) were increased and one (aldolase b) was decreased in liver tumor tissues. In addition, the expression of these genes in 6 hepatoma cell lines was also showed by RT-PCR analysis. CONCLUSION: cDNA microarray permits a high throughput identification of changes in gene expression. The genes encoding Beclin 1, RbAp48, Pir51 and aldolase b are first reported that may be related with hepatocarcinoma.

Mutation analysis of novel human liver-related putative tumor suppressor gene in hepatocellular carcinoma.

AIM: To find the point mutations meaningful for inactivation of liver-related putative tumor suppressor gene (LPTS) gene, a human novel liver-related putative tumor suppressor gene and telomerase inhibitor in hepatocellular carcinoma. METHODS: The entire coding sequence of LPTS gene was examined for mutations by single strand conformation polymorphism (SSCP) assay and PCR products direct sequencing in 56 liver cancer cell lines, 7 ovarian cancer and 7 head neck tumor cell lines and 70 pairs of HCC tissues samples. The cDNA fragment coding for the most frequent mutant protein was subcloned into GST fusion expression vector. The product was expressed in E.coli and purified by glutathione-agarose column. Telomeric repeat amplification protocol (TRAP) assays were performed to study the effect of point mutation to telomerase inhibitory activity. RESULTS: SSCP gels showed the abnormal shifting bands and DNA sequencing found that there were 5 different mutations and/or polymorphisms in 12 tumor cell lines located at exon2, exon5 and exon7. The main alterations were A(778)A/G and A(880)T in exon7. The change in site of 778 could not be found in HCC tissue samples, while the mutation in position 880 was seen in 7 (10 %) cases. The mutation in the site of 880 had no effect on telomerase inhibitory activity. CONCLUSION: Alterations identified in this study are polymorphisms of LPTS gene. LPTS mutations occur in HCC but are infrequent and of little effect on the telomerase inhibitory function of the protein. Epigenetics, such as methylation, acetylation, may play the key role in inactivation of LPTS.

Over-expression of LPTS-L in hepatocellular carcinoma cell line SMMC-7721 induces crisis.

AIM: To evaluate the function of the longer transcripts LPTS-L in hepatocellular carcinoma cell line SMMC-7721. METHODS: SMMC-7721 cells were transfected with LPTS-L expression construct and stably transfected cells were selected by G418. Multiple single clones formed and were checked for their phenotype. In the study of the effect on telomerase activity of LPTS-L in vitro, GST-LPTS-L fusion protein was expressed in E.coli and purified by glutathione-agarose column. Telomeric repeat amplification protocol (TRAP) assays were performed to study the influence of telomerase activity in SMMC-7721 cells. RESULTS: Over-expression of LPTS-L induced SMMC-7721 cells into crisis. LPTS-L could inhibit the telomerase activity in SMMC-7721 cells in vitro. CONCLUSION: LPTS-L is a potent telomerase inhibitor. Over-expression of LPTS-L can induce hepatoma cells into crisis due to the reduction of telomerase activity.

p73beta inhibits transcriptional activities of enhancer I and X promoter in hepatitis B virus more efficiently than p73alpha.

AIM: p73, as a novel member of a family of p53-related transcription factors, shares redundant functions with p53, such as the abilities of inducing apoptosis and suppressing growth. It is well known that p53 can repress HBV expression and transcription efficiently. The aim of this paper is to investigate the transcriptional effect of p73alpha and p73beta on hepatitis B virus (HBV) and to understand the correlation between HBV and p73. METHODS: To construct an x-gene inactivated HBV plasmid which was cotransfected with p73alpha or p73beta expression vectors into HepG2 cells. After transiently transfection, HBV surface antigen (HBsAg) and HBV e antigen (HBeAg) were detected by ELISA. Viral transcripts synthesized by HBV were evaluated by Northern blotting analysis. The activities of HBV regulatory elements, including enhancer I/X promoter (ENI/Xp) and enhancer II/core promoter (ENII/Cp) were monitored by luciferase assays. RESULTS: Both p73alpha and p73beta could repress HBsAg and HBeAg expression by downregulating the ENI/Xp and ENII/Cp activities. But p73beta exerted stronger inhibition on the activity of ENI/Xp than p73alpha, resulting in much lower level of viral transcripts and the antigens expression. CONCLUSION: p73beta as a novel member of p53 family can efficiently inhibit HBV transcription mainly through downregulating the activities of the HBV ENI/Xp regulatory elements.

[The cloning and expression of a novel mouse gene mLPTS and its subcellular localization].

A novel mouse gene mLPTS was cloned by EST assembling, RT-PCR and DNA sequencing. The gene fragment for mLPTS is 1244 bp in length, encoding a protein of 332 amino acids. The amino acid sequence of mLPTS has 78% homologue with that of LPTS gene, which is a novel liver cancer-related gene identified through positional candidate cloning stratage by our laboratory. The expression of LPTS gene was ubiquitous in normal human tissues, whereas levels appeared to be significantly reduced, or sometime undetectable in HCC cells and neoplastic tissues, and it might be involved in the negative regulation of cell proliferation. The expression of mLPTS gene was found in all mouse tissues analyzed, same with that of LPTS gene in human. There was only one transcript for mLPTS gene in mouse tissues. The phylogenetic tree was constructed through the amino acids sequence analysis and the study of the sequence homologue among different species. Next, mLPTS gene was cloned into green fluorescent protein eukarytic expression vector and then transfected into CHO cell line. The green fluorescent was mostly limited in the nucleolus, showing that the gene products of mLPTS in eukaryocytes were located in the nucleolus.

Cloning and Characterization of fup1, A Gene Highly Expressed in Hepatocellular Carcinoma.

Primary hepatocellular carcinoma(HCC) is one of the common malignant tumors in China. In our previous work, a gene named fup1(function-unknown protein 1) was isolated that was expressed differently in HCC and in normal liver. We assumed that it might be a candidate oncogene for the HCC. The fup1 gene had a ORF of 1 233 bp, encoding a protein with M(r) of 46 kD and isoelectric point of 5.48. The sequence characteristics showed its possible localization in nuclei. Northern blots showed that this gene was weakly expressed in many types of human tissues, except in the heart, implying its tissue-specific expression pattern. MTT assay of the NIH 3T3 cells transfected with this gene in the form of recombinant eukaryotic expression plasmid showed its enhancing role to cellular proliferation.

Identification of Up-regulated Genes in Rat Regenerating Liver Tissue by Suppression Subtractive Hybridization.

Suppression subtractive hybridization (SSH) technique was used to screen up-regulated genes in regenerating liver. The cDNA from rat regenerating liver tissue was used as the tester, and that from normal liver was used as the driver. After cloning, a subtraction cDNA library of 900 clones was obtained. These 900 clones were further analyzed by differential gene expression screening, and 50 clones with obvious overexpression in regenerating liver were identified. Sequencing analysis and homology searching showed that these clones represent 37 genes, 13 of them are homologous to genes known to be involved in liver regeneration 15 are known genes which are first found to be up-regulated in regenerating liver and 9 are novel genes (ESTs) which have been deposited to GenBank. RNA dot blotting analysis was used to further study the gene expression patterns. The results not only confirmed the up-regulation of these genes in regenerating liver tissue, but also showed that these genes had different expression patterns during the process of liver regeneration. The results implied that these genes might play important roles in liver regeneration.

Regulation of Gene Expression by SAR of Silkworm Attacus ricini rRNA Gene.

The 1 kb scaffold-attachment region (SAR) at 5' non-transcription region of rRNA gene of silkworm Attacus ricini was cloned into eukaryotic expression vector pLu, which contained luciferase report gene and neo(R) selecting marker. After transfection of constructs into NIH3T3 cell line by using cation liposome, the luciferase activity was monitored to check the SAR's function. The results demonstrated that the SAR could enhance gene expression up to 15-fold in stable transformed cells, but no obvious gene expression was observed in transient transfection. Its effect on gene expression appeared to requirechromosomal integration. Southwestern blotting experiments showed that SAR specifically bound to nuclear matrix proteins of NIH3T3 cells. The binding with nuclear matrix may be necessary for SAR function of transcriptional enhancement.

Detection of Lis1 Gene Frame Shift Mutation in Human Hepatocarcinoma.

GST fusion protein expression system combined with protein truncation test(PTT) protocol was used to detect gene frame shift mutation. The RT-PCR products of Lis1 genes from hepatocarcinoma samples were respectively cloned into a GST fusion protein expression vector pGEX-1, then expressed in E.coli. The results showed a truncated 33 kD fusion protein in SDS-PAGE, although the full-translated product of Lis1 gene should be of 71 kD. Sequencing revealed insertion of an A residue, causing the premature termination of translation, between the 163th and 164th nucleotide of Lis1 gene. This improved PTT assay was proved to be a fast and effective way in detecting gene frame shift mutation.

The Autonomous Replication Function (ARS) of the Scaffold-associated Region (SAR) of Silkworm Attacus ricini rDNA in Yeast.

The one kilo-base scaffold-associated region (SAR) of silkworm Attacus ricini rRNA gene (rDNA) has been identified previously([1]). To investigate the critical sequence and the relative activity of ARS (autonomously replicating sequence), a set of restriction from covered the whole rRNA gene unit were subcloned into the nonreplicative pSKY vector. Among the seven plasmids constructed, the plasmid pSEY, having SAR, gave obvious positive replication activity in yeast as determined by the transformation efficiency. Further dissection of SAR demonstrated that plasmid pAAY, having a 0.26 kb small fragment of SAR was 40-50 fold more active then the whole SAR, while pSAY, having the remaining part of SAR, showed no activity. There were fifteen ARS consensus sequences (ACSs) within SAR being identified through sequenced alignment. It was found that only three ACSs in pAAY, located at the 3' end of SAR displayed a positive ARS activity and the remaining sequence having the other twelve ACSs functioned as a repressor. The in vitro binding assay showed that SAR from the silkworm rRNA gene bound to the yeast nuclear scaffold. These results suggest that SAR is evolutionarily conserved, and there is a close correlation between SAR and ARS activity. Detailed analysis of the positive and negative regulatory elements in SAR can be carried out based on these results.

The DNA Sequence and Structural Characteristic of The 5'-Nontranscribed Spacer of Silkworm Attacus ricini rDNA.

We have found that the SacII-EcoRI fragment in the nontranscribed spacer (NTS) of silkworm Attacus ricini rDNA is a nuclear scaffold-associated region (SRA) and showed the function as the ARS element in yeast. This paper reports the sequence of this NTS region and the various characteristic potential functional motifs as analyzed by computer. It is 1 025 bp long and AT-Rich. With 9 bent DNA motifs, 10 T-boxes, 5 A-boxes motifs, 13 topoisomerase II as well as 15 ARS consensus sequences. In addition, there are several dozens of inverted repeats and ATTA/TAAT, ATTTA/TAAAT, ATATTT/AAATAT motifs commonly believed to be the binding sites of many homeodomain proteins. These motifs, concentrated in the SAR region, may play very important role in the regulation of gene transcription and replication at the chromatin level.