Effect of histone modifications on hMLH1 alternative splicing in gastric cancer.

hMLH1 is one of the mismatch genes closely related to the occurrence of gastric cancer. Epigenetic regulation may play more important roles than gene mutations in DNA damage repair genes to drive carcinogenesis. In this article, we discuss the role of epigenetic changes, especially histone modifications in the regulation of hMLH1 alternative splicing. Our results showed that hMLH1 delEx10, delEx11, delEx10-11, delEx16 and delEx17 transcripts were ubiquitous in sporadic Chinese gastric cancer patients and gastric cancer cell lines. Lower level of H4K16ac and H3ac was detected in hMLH1 exon 10-11 region in gastric cancer cell lines when compared with human gastric mucosal epithelial cell line GES-1. A significant decrease of hMLH1 delEx11 and delEx10-11 was observed in gastric cancer cell lines after trichostatin A treatment. H3K36me3 and H3K4me2 levels were lower in hMLH1 exon 10-11 and exon 16-17 regions in gastric cancer lines when compared with GES-1. Aberrant transcripts such as hMLH1 delEx11 and delEx10-11 were significantly higher in gastric cancer cell lines after small interfering RNA-mediated knockdown of SETD2 (the specific methyltransferase of H3K36). The hMLH1 delEx10 and delEx10-11 transcripts were increased after interference of SRSF2. Taken together, our study demonstrates that lower level of histone acetylation and specific histone methylation such as H3K36me3 correlate with aberrant transcripts in hMLH1 exon 10-11 region. SRSF2 may be involved in these specific exons skipping as well.

Epigenetic regulation of CDH1 exon 8 alternative splicing in gastric cancer.

BACKGROUND: The tumor suppressor gene CDH1 is critical for intercellular adhesion. In our previous work, we reported a nonfunctional CDH1 transcript that lacks the final 83 base pairs of exon 8 (1054del83). In this work, we probed the role of histone epigenetic modifications as well as DNA methylation in selection of this isoform. METHODS: RT-qPCR was used to detect CDH1 RNA expression. Methylation of CDH1 was analyzed by bisulphite sequencing PCR. ChIP assay was performed to show histones level. Cell lines were treated with DNA methyltransferase inhibitor AZA, HDAC inhibitor TSA, or siRNA oligonucleotides to test regulation of CDH1 splicing. RESULTS: Greater CDH1 1054del83 transcripts were observed in gastric cancer (GC) cell lines than human gastric mucosal epithelial cell line GES-1. All the cell lines showed significant methylation pattern at the CpG sites of CDH1 exon 8. AZA treatment did not influence selection of 1054del83 transcripts. A significant decrease in acetylation for histones H3 and H4K16Ac in an internal region of the CDH1 gene surrounding the alternative exon 8 were detected in GC cell lines. Treatment with TSA preferentially expressed the correctly spliced transcript and not the exon 8 skipped aberrant transcripts, showing that histone acetylation was involved in the splicing regulation. SiRNA-mediated knockdown of SETD2 (The specific methyltransferase of H3K36) decreased exclusion of exon 8, suggesting that the presence of this mark correlates with increased skipping of the final 83 base pairs of CDH1 exon 8. However, CDH1 splicing was not affected by SRSF2 knockdown. CONCLUSIONS: H3K36me3 correlates with increased skipping of the final 83 base pairs of CDH1 exon 8. Histone acetylation was involved in the splicing regulation as well.

[Establishment of a hMSH2/hMSH6 protein interaction system and functional evaluation of hMSH2 gene missense mutations].

OBJECTIVE: To construct a hMSH2/hMSH6 protein interaction system, and to use it for evaluating missense mutations detected in hMSH2 gene. METHODS: Recombinant plasmids pGADT7-hMSH2, pGBKT7-hMSH6 and 7 recombinant pGBKT7 plasmids with different hMSH6 domains were constructed through genetic engineering. Subsequently, site-directed mutagenesis was used to construct 10 mutant pGADT7-hMSH2 plasmids, which were transformed into yeast AH109. The growth of transformants was observed on a histidine-deficient culture. RESULTS: Both hMSH6 MutSII-V and MutSIII-V could interact with hMSH2 in yeast AH109. Yeast two-hybrid transformants pGADT7-hMSH2/pGBKT7-hMSH6 MutSII-V were used to construct a hMSH2/hMSH6 protein interaction system. Compared with wild-type hMSH2, yeast two-hybrid transformants c.505A>G, c.1168C>T, c.1255C>A, c.1261C>A could grow normally, c.1223A>G, c.1886A>G, c.2108C>A and c.2516A>G grew slowly, c.518T>G and c.1664 delA could not grow in a histidine-deficient medium in yeast AH109. CONCLUSION: A hMSH2/hMSH6 protein interaction system has been constructed with yeast two-hybrid system, which has been used for functional evaluation of hMSH2 gene missense mutations. c.518T>G is a pathological mutation. c.1223A>G, c.1886A>G, c.2108C>A, c.2516A>G may in part affect the hMSH2 function. And c.505A>G, c.1168C>T, c.1255C>A, c.1261C>A were innocuous variants.

Novel CDH1 germline mutations identified in Chinese gastric cancer patients.

AIM: To give a comprehensive report of E-cadherin gene (CDH1) variations in a population at a high risk for gastric cancer (GC). METHODS: The samples consisted of 178 men and 58 women with a mean age of 62.3 ± 9.4 years and an age range of 30-84 years. A total of 240 cancer-free controls were recruited (mean age of 61.8 ± 10.1 years, age range of 26-82 years). Samples were screened for CDH1 germline mutations by high-resolution melting analysis or directly sequencing. Luciferase reporter assay, RNA splicing assay and bioinformatic analysis were used to evaluate the effect of mutations. RESULTS: Four novel CDH1 sequence alterations were identified in GC patients including a G>T transition 49 bp before the start codon; a three-nucleotide deletion, c.44_46del TGC; one missense mutation, c.604G>A (V202I); and one variation in the intron, c.1320+7A>G. In addition, polymorphism frequencies were observed for CDH1-164delT, -161C>A, -73A>C, c.48+6C>T, c.48+62_48+63delinsCGTGCCCCAGCCC, c.894C>T (A298A), c.1224G>A (A408A), c.1888C>G (L630V), c.2076T>C (A692A), and c.2253C>T (N751N) which is similar to the data reported in http://www.ncbi.nlm.nih.gov/projects/SNP/. RNA splicing analysis suggested that the c.1320+7A>G and c.1224G>A variations did not affect exon splicing ability. Luciferase reporter assay demonstrated that the c.-49T variation might be helpful for E-cadherin transcription, though the increase in transcription activity is limited (only 33%). SIFT score and PolyPhen analysis both demonstrated that the L630V missense mutation probably damages protein function, while the V202I variant does not. CONCLUSION: This study reveals novel mutations in sporadic GC patients which had been poorly investigated for susceptibility genes.

Germline promoter hypermethylation of tumor suppressor genes in gastric cancer.

AIM: To explore germline hypermethylation of the tumor suppressor genes MLH1, CDH1 and P16(INK4a) in suspected cases of hereditary gastric cancer (GC). METHODS: A group of 140 Chinese GC patients in whom the primary cancer had developed before the age of 60 or who had a familial history of cancer were screened for germline hypermethylation of the MLH1, CDH1 and P16(INK4a) tumor suppressor genes. Genomic DNA was extracted from peripheral blood leukocytes and modified by sodium bisulfite. The treated DNA was then subjected to bisulfite DNA sequencing for a specific region of the MLH1 promoter. The methylation status of CDH1 or P16(INK4a) was assayed using methylation-specific PCR. Clonal bisulfite allelic sequencing in positive samples was performed to obtain a comprehensive analysis of the CpG island methylation status of these promoter regions. RESULTS: Methylation of the MLH1 gene promoter was detected in the peripheral blood DNA of only 1/140 (0.7%) of the GC patient group. However, this methylation pattern was mosaic rather than the allelic pattern which has previously been reported for MLH1 in hereditary non-polyposis colorectal cancer (HNPCC) patients. We found that 10% of the MLH1 alleles in the peripheral blood DNA of this patient were methylated, consistent with 20% of cells having one methylated allele. No germline promoter methylation of the CDH1 or P16(INK4a) genes was detected. CONCLUSION: Mosaic germline epimutation of the MLH1 gene is present in suspected hereditary GC patients in China but at a very low level. Germline epimutation of the CDH1 or P16(INK4a) gene is not a frequent event.

[Germ-line epimutations and human cancer].

Epimutations are errors in the normal process of epigenetic regulation which can result in aberrant transcriptional silencing of a normally active gene or reactivation of a normally silent gene. Epimutations are generally considered to be somatic events and to be confined in affected tissues. However, recent studies of patients with hereditary nonpolyposis colorectal cancer (HNPCC) have showed that allele-specific hypermethylation of CpG islands in the promoter region of the MLH1 gene, one of the causes of the tumor, existed in all the tissues examined. In addition, germ-line epimutations of other tumor suppressor genes (TSGs), such as MSH2 and BRCA1, have also been reported, demonstrating that epimutations might arise in the germ-line (during gametogenesis or early embryonic development). The role of germ-line epimutations might be as important as germ-line mutations in human disease. We reviewed the update on germ-line epimutations of TSGs including the possible mechanisms underlying germ-line epimutations, the possibility of transgenerational inheritance, and their impact on our understanding of human disease.

Effective protection of Terminalia catappa L. leaves from damage induced by carbon tetrachloride in liver mitochondria.

The protective effects of chloroform extracts of Terminalia catappa L. leaves (TCCE) on carbon tetrachloride (CCl4)-induced liver damage and the possible mechanisms involved in the protection were investigated in mice. We found that increases in the activity of serum aspartate aminotransferase and alanine aminotransferase and the level of liver lipid peroxidation (2.0-fold, 5.7-fold and 2.8-fold) induced by CCl4 were significantly inhibited by oral pretreatment with 20, 50 or 100 mg/kg of TCCE. Morphological observation further confirmed the hepatoprotective effects of TCCE. In addition, the disruption of mitochondrial membrane potential (14.8%), intramitochondrial Ca2+ overload (2.1-fold) and suppression of mitochondrial Ca2+-ATPase activity (42.0%) in the liver of CCl4-insulted mice were effectively prevented by pretreatment with TCCE. It can be concluded that TCCE have protective activities against liver mitochondrial damage induced by CCl4, which suggests a new mechanism of the hepatoprotective effects of TCCE.

Inhibitory effect of TCCE on CCl4-induced overexpression of IL-6 in acute liver injury.

Terminalia catappa L. leaves have been shown to protect against acute liver injury produced by some hepatotoxicants, but the active components and mechanisms are not clear. This study was designed to characterize the protective effects of the chloroform fraction of the ethanol extract of T. catappa leaves (TCCE) against carbon tetrachloride (CCl4)-induced hepatotoxicity in mice, and analyze the changes in expression level of interleukin-6 (IL-6) in the process. It was found that TCCE pretreatment (10 or 30 mg/kg, ig) protected mice from CCl4 toxicity, as evidenced by the reversed alterations in serum alanine aminotransferase (sALT) and serum aspartate aminotransferase (sAST) activities. Additionally liver tissues were subjected to RT-PCR, Western blot and immunohistochemistry to analyze changes in IL-6 expression. It was found that TCCE markedly suppressed the CCl4-induced over-transcription of IL-6 gene. Consistent with the result, the expression of IL-6 protein was also blocked by TCCE in CCl4-stimulated mice, especially in the area around central vein on liver tissue section. In conclusion, TCCE is effective in protecting mice from the hepatotoxicity produced by CCl4, and the mechanisms underlying its protective effects may be related to the inhibition on the overexpression of IL-6 mainly around terminal hepatic vein.