BACKGROUND Post-translational modifications play key roles in various biological processes.Protein arginine methyltransferases(PRMTs)transfer the methyl group to specific arginine residues.Both PRMT1 and PRMT6 have em...BACKGROUND Post-translational modifications play key roles in various biological processes.Protein arginine methyltransferases(PRMTs)transfer the methyl group to specific arginine residues.Both PRMT1 and PRMT6 have emerges as crucial factors in the development and progression of multiple cancer types.We posit that PRMT1 and PRMT6 might interplay directly or in-directly in multiple ways accounting for shared disease phenotypes.AIM To investigate the mechanism of the interaction between PRMT1 and PRMT6.METHODS Gel electrophoresis autoradiography was performed to test the methyltranferase activity of PRMTs and characterize the kinetics parameters of PRMTs.Liquid chromatography-tandem mass spectrometryanalysis was performed to detect the PRMT6 methylation sites.RESULTS In this study we investigated the interaction between PRMT1 and PRMT6,and PRMT6 was shown to be a novel substrate of PRMT1.We identified specific arginine residues of PRMT6 that are methylated by PRMT1,with R106 being the major methylation site.Combined biochemical and cellular data showed that PRMT1 downregulates the enzymatic activity of PRMT6 in histone H3 methylation.CONCLUSION PRMT6 is methylated by PRMT1 and R106 is a major methylation site induced by PRMT1.PRMT1 methylation suppresses the activity of PRMT6.展开更多
AIM: To investigate the functions of promoter hypermethylation of O6-methylguanine-DNA methyltransferase (MGMT) gene in colorectal tumorigenesis and progression.METHODS: The promoter hypermethylation of MGMT gene was ...AIM: To investigate the functions of promoter hypermethylation of O6-methylguanine-DNA methyltransferase (MGMT) gene in colorectal tumorigenesis and progression.METHODS: The promoter hypermethylation of MGMT gene was detected in 27 sporadic colorectal adenomas,62 sporadic colorectal carcinomas and 20 normal colorectal mucosa tissues by methylation-specific PCR. At the same time, the expression of MGMT protein was carried out in the same samples using immunohistochemistry. Mutantallele-specific amplification was used to detect K-rasG to A point mutation in codon 12.RESULTS: None of the normal colorectal mucosa tissues showed methylated bands. Promoter hypermethylation was detected in 40.7% (11 of 27) of adenomas and 43.5% (27 of 62) of carcinomas. MGMT proteins were expressed in nucleus and cytoplasm of normal colorectal mucosa tissues. Loss of MGMT expression was found in 22.2% (6 of 27) of adenomas and 45.2% (28 of 62) of carcinomas. The difference between them was significant (P = 0.041). In the 6 adenomas and 28 carcinomas losing MGMT expression, 5 and 24 cases presented methylation,respectively (P = 0.027, P＜0.001). Thirteen of the 19 colorectal tumors with K-rasG to A point mutation in codon 12 had methylated MGMT(P = 0.011). The frequencies of K-rasG to A point mutation were 35.3% (12 of 34) and 12.7% (7 of 55) in tumors losing MGMT expression and with normal expression, respectively.CONCLUSION: Promoter hypermethylation and loss of expression of MGMT gene were common events in colorectal tumorigenesis, and loss of expression of MGMT occurs more frequently in carcinomas than in adenomas in sporadic patients. Hypermethylation of the CpG island of MGMT gene was associated with loss of MGMT expression and K-ras G to A point mutation in colorectal tumor. The frequency of K-ras G to A point mutation was increased in tumors losing MGMT expression. It suggests that epigenetic inactivation of MGMT plays an important role in colorectal neoplasia.展开更多
BACKGROUND O_(6)-methylguanine-DNA methyltransferase(MGMT)is a suicide enzyme that repairs the mispairing base O_(6)-methyl-guanine induced by environmental and experimental carcinogens.It can transfer the alkyl group...BACKGROUND O_(6)-methylguanine-DNA methyltransferase(MGMT)is a suicide enzyme that repairs the mispairing base O_(6)-methyl-guanine induced by environmental and experimental carcinogens.It can transfer the alkyl group to a cysteine residue in its active site and became inactive.The chemical carcinogen N-nitroso compounds(NOCs)can directly bind to the DNA and induce the O_(6)-methylguanine adducts,which is an important cause of gene mutation and tumorigenesis.However,the underlying regulatory mechanism of MGMT involved in NOCs-induced tumorigenesis,especially in the initiation phase,remains largely unclear.AIM To investigate the molecular regulatory mechanism of MGMT in NOCs-induced gastric cell malignant transformation and tumorigenesis.METHODS We established a gastric epithelial cell malignant transformation model induced by N-methyl-N’-nitro-N-nitrosoguanidine(MNNG)or N-methyl-N-nitroso-urea(MNU)treatment.Cell proliferation,colony formation,soft agar,cell migration,and xenograft assays were used to verify the malignant phenotype.By using quantitative real-time polymerase chain reaction(qPCR)and Western blot analysis,we detected the MGMT expression in malignant transformed cells.We also confirmed the MGMT expression in early stage gastric tumor tissues by qPCR and immunohistochemistry.MGMT gene promoter DNA methylation level was analyzed by methylation-specific PCR and bisulfite sequencing PCR.The role of MGMT in cell malignant transformation was analyzed by colony formation and soft agar assays.RESULTS We observed a constant increase in MGMT mRNA and protein expression in gastric epithelial cell malignant transformation induced by MNNG or MNU treatment.Moreover,we found a reduction of MGMT gene promoter methylation level by methylation-specific PCR and bisulfite sequencing PCR in MNNG/MNU-treated cells.Inhibition of the MGMT expression by O_(6)-benzylguanine promoted the MNNG/MNU-induced malignant phenotypes.Overexpression of MGMT partially reversed the cell malignant transformation process induced by MNNG/MNU.Clinical gastric tissue analysis showed that MGMT was upregulated in the precancerous lesions and metaplasia tissues,but downregulated in the gastric cancer tissues.CONCLUSION Our finding indicated that MGMT upregulation is induced via its DNA promoter hypomethylation.The highly expressed MGMT prevents the NOCs-induced cell malignant transformation and tumorigenesis,which suggests a potential novel approach for chemical carcinogenesis intervention by regulating aberrant epigenetic mechanisms.展开更多
O6-methylguanine-DNA methyltransferase (MGMT) plays an important role in repairing alkylated DNA. MGMT activity as well as cellular sensitivity to 1- ( 4- amino- 2-methyl-5-pyrimidinyl) methyl-3- ( 2-chloroethyl)-3-ni...O6-methylguanine-DNA methyltransferase (MGMT) plays an important role in repairing alkylated DNA. MGMT activity as well as cellular sensitivity to 1- ( 4- amino- 2-methyl-5-pyrimidinyl) methyl-3- ( 2-chloroethyl)-3-nitrosourea (ACNU) of 20 Chinese tumor cell strains were assayed. A linear response between MGMT activity and ACNU sensitivity (D10) was observed. The lower the MGMT activity In the cells, the more the sensitivity to ACNU killing. It suggested that assay of MGMT activity in tumor biopsy could be used as a guide to predict the effectiveness of ACNU treatment in chemotherapy of human cancer.展开更多
The tumor selectivity of alkylating agents that produce guanine O6-chloroethyl (laromustine and carmustine) and O6-methyl (temozolomide) lesions depends upon O6-methylguanine-DNA methyltransferase (MGMT) activity bein...The tumor selectivity of alkylating agents that produce guanine O6-chloroethyl (laromustine and carmustine) and O6-methyl (temozolomide) lesions depends upon O6-methylguanine-DNA methyltransferase (MGMT) activity being lower in tumor than in host tissue. Despite the established role of MGMT as a tumor resistance factor, consensus on how to assess MGMT expression in clinical samples is unsettled. The aim of this study is to examine the relationship between the values derived from distinctive MGMT measurements in 13, 12, 6 and 2 pairs of human tumors and matched normal adjacent tissue from the colon, kidney, lung and liver, respectively, and in human cell lines. The MGMT measurements included 1) alkyl-transfer assays using [benzene-3H]O6-benzylguanine as a substrate to assess functional MGMT activity, 2) methylation-specific PCR (MSP) to probe MGMT gene promoter CpG methylations as a measure of gene silencing, and 3) western immunoblots to analyze the MGMT protein. In human cell lines, a strict negative correlation existed between MGMT activity and the extent of promoter methylation. In tissue specimens, by contrast, the correlation between these two variables was low. Moreover, alkyl-transfer assays identified 3 pairs of tumors and normal tissue with tumor-selective reduction in MGMT activity in the absence of promoter methylation. Cell line MGMT migrated as a single band in western analyses, whereas tissue MGMT was heterogeneous around its molecular size and at much higher molecular masses, indicative of multi-layered post-translational modifications. Malignancy is occasionally associated with a mobility shift in MGMT. Contrary to the prevalent expectation that MGMT expression is governed at the level of gene silencing, these data suggest that other mechanisms that can lead to tumorselective reduction in MGMT activity exist in human tissue.展开更多
Methylation of the N6 position of adenine, termed N6-methyladenine, protects DNA from restriction endonucleases via the host-specific restriction-modification system. N6-methyladenine was discovered and has been well ...Methylation of the N6 position of adenine, termed N6-methyladenine, protects DNA from restriction endonucleases via the host-specific restriction-modification system. N6-methyladenine was discovered and has been well studied in bacteria. N6-adenine-specific DNA methyltransferase（N6AMT） is the main enzyme catalyzing the methylation of the adenine base and knowledge of this enzyme was mainly derived from work in prokaryotic models. However, large-scale gene discovery at the genome level in many model organisms indicated that the N6AMT gene also exists in eukaryotes, such as humans, mice, fruit flies and plants. Here, we cloned a N6AMT gene from Nilaparvata lugens（Nlu-N6AMT） and amplified its fulllength transcript. Then, we carried out a systematic investigation of N6AMT in 33 publically available insect genomes, indicating that all studied insects had N6AMT. Genomic structure analysis showed that insect N6AMT has short introns compared with the mammalian homologs. Domain and phylogenetic analysis indicated that insect N6AMT had a conserved N6-adenine Mlase domain that is specific to catalyze the adenine methylation. Nlu-N6AMT was highly expressed in the adult female. We knocked down Nlu-N6AMT by feeding ds RNA from the second instar nymph to adult female, inducing retard development of adult female. In all, we provide the first genome-wide analysis of N6AMT in insects and presented the experimental evidence that N6AMT might have important functions in reproductive development and ovary maturation.展开更多
Spinal cord injury typically causes corticospinal tract disruption. Although the disrupted corticospinal tract can self-regenerate to a certain degree, the underlying mechanism of this process is still unclear. N6-met...Spinal cord injury typically causes corticospinal tract disruption. Although the disrupted corticospinal tract can self-regenerate to a certain degree, the underlying mechanism of this process is still unclear. N6-methyladenosine(m^(6)A) modifications are the most common form of epigenetic regulation at the RNA level and play an essential role in biological processes. However, whether m^(6)A modifications participate in corticospinal tract regeneration after spinal cord injury remains unknown. We found that expression of methyltransferase 14 protein(METTL14) in the locomotor cortex was high after spinal cord injury and accompanied by elevated m^(6)A levels. Knockdown of Mettl14 in the locomotor cortex was not favorable for corticospinal tract regeneration and neurological recovery after spinal cord injury. Through bioinformatics analysis and methylated RNA immunoprecipitation-quantitative polymerase chain reaction, we found that METTL14 regulated Trib2 expression in an m^(6)A-regulated manner, thereby activating the mitogen-activated protein kinase pathway and promoting corticospinal tract regeneration. Finally, we administered syringin, a stabilizer of METTL14, using molecular docking. Results confirmed that syringin can promote corticospinal tract regeneration and facilitate neurological recovery by stabilizing METTL14. Findings from this study reveal that m^(6)A modification is involved in the regulation of corticospinal tract regeneration after spinal cord injury.展开更多
Objective:This phase II study aimed at investigating the correlation between O6-methylguanine-DNA methyltransferase (MGMT) promoter methylation and protein expression,together with Ki-67 labeling index (LI),to respons...Objective:This phase II study aimed at investigating the correlation between O6-methylguanine-DNA methyltransferase (MGMT) promoter methylation and protein expression,together with Ki-67 labeling index (LI),to response,time to progression (TTP),and overall survival (OS) in newly diagnosed glioblastoma multiforme (GBM) patients treated with temozolomide (TMZ) concomitant with and adjuvant to radiotherapy (RT).Methods:From June 2005 to August 2008,34 adult patients (18-65 years),PS ≥70,with newly diagnosed GBM received TMZ 75 mg/m2 plus RT up to 60 Gy,followed by TMZ 175 mg/m2 5 days every 4 weeks for 12 doses.MGMT Methylation-specific PCR assay,MGMT protein expression,and Ki-67 expression using immunohistochemistry (IHC) were performed on the tissue blocks.The patients were followed by MRI while MR spectroscopy (MRS) was performed for the stable cases or to confirm progression and accordingly Bevacizumab 10 mg/kg every 2 weeks was added to 7 patients till further progression was proved.Results:31 cases were evaluable,12 (38.7%) had unmethylated MGMT,while 19 (61.3%) were methylated.Seventeen cases (55%) were MGMT immunonegative while 14 cases (45%) were immunopositive.The cut off value of Ki-67 LI in relation to survival was 17%,where 15 were < 17% (48.4%),and 16 were ≥ 17% (51.6%).Response evaluation started after the second dose of the adjuvant TMZ and was repeated every 2 months.The overall disease control rate (ODC) was 74.2%,where 2 patients had complete response (CR),14 had partial response (PR),and 7 had stable disease (SD),while 8 (25.8%) had progressive disease (PD).The ODC was significantly higher among methylated patients and in those with Ki-67 < 17% (P=0.0003).The median overall TTP was 12 months and the median OS was 20 months for all the patients including those who received Bevacizumab for some stable cases or as a salvage treatment in patients with good PS,the MGMT-methylated patients had a higher median TTP of 13 months (range 8 to 18 months,95% CI of 9.36 to 12.9),and OS of 24 months (range 12 to 31 months,95% CI of 16.1 to 21.32),while the unmethylated patients had a median TTP of 6.5 months and a median OS of 12 months,such correlations were highly significant (P=0.0001).MGMT immunoexpression failed to show significant correlation with MGMT promotor methylation or the outcome of the patients.Patients with Ki-67 < 17% had a median TTP of 16 months and median OS of 24 months compared to 7 and 12.5 months respectively for the patients with Ki-67 ≥17%.Significant correlation was found between the ODC,TTP,and OS with age < 52,near total excision,and TMZ doses received ≥ 10.The commonest grade 3 and 4 toxicities was neutropenia recorded in 3 patients (9.67%),thrombocytopenia in 4 patients (12.9%),and one patient with G3 nausea,vomiting,and constipations (3%),all were medically manageable.Conclusion:MGMT promotor methylation status and Ki-67 LI (but not the MGMT protein expression),could serve as prognostic markers for survival,also MGMT could identify the newly diagnosed GBM patients who will have better response to TMZ.展开更多
目的 探讨外周血单核细胞DNA甲基化转移酶1(DNMT1)及血清白介素-6(IL-6)在糖尿病肾脏病(DKD)中的表达及临床意义。方法 选取150例DKD患者(DKD组)及50例同期健康体检者(对照组)。比较2组IL-6、DNMT1、总胆固醇、三酰甘油、高密度脂蛋白...目的 探讨外周血单核细胞DNA甲基化转移酶1(DNMT1)及血清白介素-6(IL-6)在糖尿病肾脏病(DKD)中的表达及临床意义。方法 选取150例DKD患者(DKD组)及50例同期健康体检者(对照组)。比较2组IL-6、DNMT1、总胆固醇、三酰甘油、高密度脂蛋白胆固醇(HDL-C)、低密度脂蛋白胆固醇(LDL-C)、血肌酐、空腹血糖、肾小球滤过率估计值(e GFR)、24 h尿白蛋白排泄率(24 h UAER)的差异。Pearson相关分析IL-6、DNMT1与其他临床指标的相关性。多因素Logistic回归分析DKD发生的影响因素。受试者工作特征(ROC)曲线分析24 h UAER、IL-6、DNMT1及联合检测对DKD的诊断价值。结果 与对照组比较,DKD组的空腹血糖、IL-6、DNMT1、血肌酐、24 h UAER、LDL-C、糖化血红蛋白水平升高,而eGFR、HDL-C水平降低(均P<0.05)。DKD组的IL-6与DNMT1呈正相关(r=0.560,P<0.05);且IL-6、DNMT1与24 h UAER呈正相关(r分别为0.551和0.570,P<0.05)。24 h UAER、IL-6及DNMT1升高是影响DKD发生的独立危险因素(P<0.05)。24 h UAER、IL-6、DNMT1联合检测诊断DKD的曲线下面积优于单一指标检测。结论 DKD患者DNMT1、IL-6水平升高,24 h UAER、DNMT1、IL-6联合检测可作为临床诊断DKD的良好指标。展开更多
The limited regenerative capacity of neuronal cells requires tight orchestration of cell death and survival regulation in the context of longevity, age-associated diseases as well as during the development of the nerv...The limited regenerative capacity of neuronal cells requires tight orchestration of cell death and survival regulation in the context of longevity, age-associated diseases as well as during the development of the nervous system. Subordinate to genetic networks epigenetic mechanisms like DNA methylation and histone modifications are involved in the regulation of neuronal development, function and aging. DNA methylation by DNA methyltransferases （DNMTs）, mostly correlated with gene silencing, is a dynamic and reversible process. In addition to their canonical actions performing cytosine methylation, DNMTs influence gene expression by interactions with histone modifying enzymes or complexes increasing the complexity of epigenetic transcriptional networks. DNMTs are expressed in neuronal progenitors, post-mi- totic as well as adult neurons. In this review, we discuss the role and mode of actions of DNMTs including downstream networks in the regulation of neuronal survival in the developing and aging nervous system and its relevance for associated disorders.展开更多
基金Supported by National Institutes of Health,No.5R01GM126154 and No.1R35GM149230。
文摘BACKGROUND Post-translational modifications play key roles in various biological processes.Protein arginine methyltransferases(PRMTs)transfer the methyl group to specific arginine residues.Both PRMT1 and PRMT6 have emerges as crucial factors in the development and progression of multiple cancer types.We posit that PRMT1 and PRMT6 might interplay directly or in-directly in multiple ways accounting for shared disease phenotypes.AIM To investigate the mechanism of the interaction between PRMT1 and PRMT6.METHODS Gel electrophoresis autoradiography was performed to test the methyltranferase activity of PRMTs and characterize the kinetics parameters of PRMTs.Liquid chromatography-tandem mass spectrometryanalysis was performed to detect the PRMT6 methylation sites.RESULTS In this study we investigated the interaction between PRMT1 and PRMT6,and PRMT6 was shown to be a novel substrate of PRMT1.We identified specific arginine residues of PRMT6 that are methylated by PRMT1,with R106 being the major methylation site.Combined biochemical and cellular data showed that PRMT1 downregulates the enzymatic activity of PRMT6 in histone H3 methylation.CONCLUSION PRMT6 is methylated by PRMT1 and R106 is a major methylation site induced by PRMT1.PRMT1 methylation suppresses the activity of PRMT6.
基金Supported by the Key Technologies R&D Program of Hubei Province, No. 2002AA301C84
文摘AIM: To investigate the functions of promoter hypermethylation of O6-methylguanine-DNA methyltransferase (MGMT) gene in colorectal tumorigenesis and progression.METHODS: The promoter hypermethylation of MGMT gene was detected in 27 sporadic colorectal adenomas,62 sporadic colorectal carcinomas and 20 normal colorectal mucosa tissues by methylation-specific PCR. At the same time, the expression of MGMT protein was carried out in the same samples using immunohistochemistry. Mutantallele-specific amplification was used to detect K-rasG to A point mutation in codon 12.RESULTS: None of the normal colorectal mucosa tissues showed methylated bands. Promoter hypermethylation was detected in 40.7% (11 of 27) of adenomas and 43.5% (27 of 62) of carcinomas. MGMT proteins were expressed in nucleus and cytoplasm of normal colorectal mucosa tissues. Loss of MGMT expression was found in 22.2% (6 of 27) of adenomas and 45.2% (28 of 62) of carcinomas. The difference between them was significant (P = 0.041). In the 6 adenomas and 28 carcinomas losing MGMT expression, 5 and 24 cases presented methylation,respectively (P = 0.027, P＜0.001). Thirteen of the 19 colorectal tumors with K-rasG to A point mutation in codon 12 had methylated MGMT(P = 0.011). The frequencies of K-rasG to A point mutation were 35.3% (12 of 34) and 12.7% (7 of 55) in tumors losing MGMT expression and with normal expression, respectively.CONCLUSION: Promoter hypermethylation and loss of expression of MGMT gene were common events in colorectal tumorigenesis, and loss of expression of MGMT occurs more frequently in carcinomas than in adenomas in sporadic patients. Hypermethylation of the CpG island of MGMT gene was associated with loss of MGMT expression and K-ras G to A point mutation in colorectal tumor. The frequency of K-ras G to A point mutation was increased in tumors losing MGMT expression. It suggests that epigenetic inactivation of MGMT plays an important role in colorectal neoplasia.
基金Supported by National Natural Science Foundation of China,No.81472543 and No.81772919Zhejiang Provincial Natural Science Foundation of China,No.LY18H160024 and No.LY20H160040
文摘BACKGROUND O_(6)-methylguanine-DNA methyltransferase(MGMT)is a suicide enzyme that repairs the mispairing base O_(6)-methyl-guanine induced by environmental and experimental carcinogens.It can transfer the alkyl group to a cysteine residue in its active site and became inactive.The chemical carcinogen N-nitroso compounds(NOCs)can directly bind to the DNA and induce the O_(6)-methylguanine adducts,which is an important cause of gene mutation and tumorigenesis.However,the underlying regulatory mechanism of MGMT involved in NOCs-induced tumorigenesis,especially in the initiation phase,remains largely unclear.AIM To investigate the molecular regulatory mechanism of MGMT in NOCs-induced gastric cell malignant transformation and tumorigenesis.METHODS We established a gastric epithelial cell malignant transformation model induced by N-methyl-N’-nitro-N-nitrosoguanidine(MNNG)or N-methyl-N-nitroso-urea(MNU)treatment.Cell proliferation,colony formation,soft agar,cell migration,and xenograft assays were used to verify the malignant phenotype.By using quantitative real-time polymerase chain reaction(qPCR)and Western blot analysis,we detected the MGMT expression in malignant transformed cells.We also confirmed the MGMT expression in early stage gastric tumor tissues by qPCR and immunohistochemistry.MGMT gene promoter DNA methylation level was analyzed by methylation-specific PCR and bisulfite sequencing PCR.The role of MGMT in cell malignant transformation was analyzed by colony formation and soft agar assays.RESULTS We observed a constant increase in MGMT mRNA and protein expression in gastric epithelial cell malignant transformation induced by MNNG or MNU treatment.Moreover,we found a reduction of MGMT gene promoter methylation level by methylation-specific PCR and bisulfite sequencing PCR in MNNG/MNU-treated cells.Inhibition of the MGMT expression by O_(6)-benzylguanine promoted the MNNG/MNU-induced malignant phenotypes.Overexpression of MGMT partially reversed the cell malignant transformation process induced by MNNG/MNU.Clinical gastric tissue analysis showed that MGMT was upregulated in the precancerous lesions and metaplasia tissues,but downregulated in the gastric cancer tissues.CONCLUSION Our finding indicated that MGMT upregulation is induced via its DNA promoter hypomethylation.The highly expressed MGMT prevents the NOCs-induced cell malignant transformation and tumorigenesis,which suggests a potential novel approach for chemical carcinogenesis intervention by regulating aberrant epigenetic mechanisms.
文摘O6-methylguanine-DNA methyltransferase (MGMT) plays an important role in repairing alkylated DNA. MGMT activity as well as cellular sensitivity to 1- ( 4- amino- 2-methyl-5-pyrimidinyl) methyl-3- ( 2-chloroethyl)-3-nitrosourea (ACNU) of 20 Chinese tumor cell strains were assayed. A linear response between MGMT activity and ACNU sensitivity (D10) was observed. The lower the MGMT activity In the cells, the more the sensitivity to ACNU killing. It suggested that assay of MGMT activity in tumor biopsy could be used as a guide to predict the effectiveness of ACNU treatment in chemotherapy of human cancer.
文摘The tumor selectivity of alkylating agents that produce guanine O6-chloroethyl (laromustine and carmustine) and O6-methyl (temozolomide) lesions depends upon O6-methylguanine-DNA methyltransferase (MGMT) activity being lower in tumor than in host tissue. Despite the established role of MGMT as a tumor resistance factor, consensus on how to assess MGMT expression in clinical samples is unsettled. The aim of this study is to examine the relationship between the values derived from distinctive MGMT measurements in 13, 12, 6 and 2 pairs of human tumors and matched normal adjacent tissue from the colon, kidney, lung and liver, respectively, and in human cell lines. The MGMT measurements included 1) alkyl-transfer assays using [benzene-3H]O6-benzylguanine as a substrate to assess functional MGMT activity, 2) methylation-specific PCR (MSP) to probe MGMT gene promoter CpG methylations as a measure of gene silencing, and 3) western immunoblots to analyze the MGMT protein. In human cell lines, a strict negative correlation existed between MGMT activity and the extent of promoter methylation. In tissue specimens, by contrast, the correlation between these two variables was low. Moreover, alkyl-transfer assays identified 3 pairs of tumors and normal tissue with tumor-selective reduction in MGMT activity in the absence of promoter methylation. Cell line MGMT migrated as a single band in western analyses, whereas tissue MGMT was heterogeneous around its molecular size and at much higher molecular masses, indicative of multi-layered post-translational modifications. Malignancy is occasionally associated with a mobility shift in MGMT. Contrary to the prevalent expectation that MGMT expression is governed at the level of gene silencing, these data suggest that other mechanisms that can lead to tumorselective reduction in MGMT activity exist in human tissue.
基金supported by the National Basic Research Program of China (2012CB114102)
文摘Methylation of the N6 position of adenine, termed N6-methyladenine, protects DNA from restriction endonucleases via the host-specific restriction-modification system. N6-methyladenine was discovered and has been well studied in bacteria. N6-adenine-specific DNA methyltransferase（N6AMT） is the main enzyme catalyzing the methylation of the adenine base and knowledge of this enzyme was mainly derived from work in prokaryotic models. However, large-scale gene discovery at the genome level in many model organisms indicated that the N6AMT gene also exists in eukaryotes, such as humans, mice, fruit flies and plants. Here, we cloned a N6AMT gene from Nilaparvata lugens（Nlu-N6AMT） and amplified its fulllength transcript. Then, we carried out a systematic investigation of N6AMT in 33 publically available insect genomes, indicating that all studied insects had N6AMT. Genomic structure analysis showed that insect N6AMT has short introns compared with the mammalian homologs. Domain and phylogenetic analysis indicated that insect N6AMT had a conserved N6-adenine Mlase domain that is specific to catalyze the adenine methylation. Nlu-N6AMT was highly expressed in the adult female. We knocked down Nlu-N6AMT by feeding ds RNA from the second instar nymph to adult female, inducing retard development of adult female. In all, we provide the first genome-wide analysis of N6AMT in insects and presented the experimental evidence that N6AMT might have important functions in reproductive development and ovary maturation.
基金supported by the National Natural Science Foundation of China,Nos.82030071 (to JH),82272495 (to YC)Science and Technology Major Project of Changsha,No.kh2103008 (to JH)Graduate Students’ Independent Innovative Projects of Hunan Province,No.CX20230311 (to YJ)。
文摘Spinal cord injury typically causes corticospinal tract disruption. Although the disrupted corticospinal tract can self-regenerate to a certain degree, the underlying mechanism of this process is still unclear. N6-methyladenosine(m^(6)A) modifications are the most common form of epigenetic regulation at the RNA level and play an essential role in biological processes. However, whether m^(6)A modifications participate in corticospinal tract regeneration after spinal cord injury remains unknown. We found that expression of methyltransferase 14 protein(METTL14) in the locomotor cortex was high after spinal cord injury and accompanied by elevated m^(6)A levels. Knockdown of Mettl14 in the locomotor cortex was not favorable for corticospinal tract regeneration and neurological recovery after spinal cord injury. Through bioinformatics analysis and methylated RNA immunoprecipitation-quantitative polymerase chain reaction, we found that METTL14 regulated Trib2 expression in an m^(6)A-regulated manner, thereby activating the mitogen-activated protein kinase pathway and promoting corticospinal tract regeneration. Finally, we administered syringin, a stabilizer of METTL14, using molecular docking. Results confirmed that syringin can promote corticospinal tract regeneration and facilitate neurological recovery by stabilizing METTL14. Findings from this study reveal that m^(6)A modification is involved in the regulation of corticospinal tract regeneration after spinal cord injury.
文摘Objective:This phase II study aimed at investigating the correlation between O6-methylguanine-DNA methyltransferase (MGMT) promoter methylation and protein expression,together with Ki-67 labeling index (LI),to response,time to progression (TTP),and overall survival (OS) in newly diagnosed glioblastoma multiforme (GBM) patients treated with temozolomide (TMZ) concomitant with and adjuvant to radiotherapy (RT).Methods:From June 2005 to August 2008,34 adult patients (18-65 years),PS ≥70,with newly diagnosed GBM received TMZ 75 mg/m2 plus RT up to 60 Gy,followed by TMZ 175 mg/m2 5 days every 4 weeks for 12 doses.MGMT Methylation-specific PCR assay,MGMT protein expression,and Ki-67 expression using immunohistochemistry (IHC) were performed on the tissue blocks.The patients were followed by MRI while MR spectroscopy (MRS) was performed for the stable cases or to confirm progression and accordingly Bevacizumab 10 mg/kg every 2 weeks was added to 7 patients till further progression was proved.Results:31 cases were evaluable,12 (38.7%) had unmethylated MGMT,while 19 (61.3%) were methylated.Seventeen cases (55%) were MGMT immunonegative while 14 cases (45%) were immunopositive.The cut off value of Ki-67 LI in relation to survival was 17%,where 15 were < 17% (48.4%),and 16 were ≥ 17% (51.6%).Response evaluation started after the second dose of the adjuvant TMZ and was repeated every 2 months.The overall disease control rate (ODC) was 74.2%,where 2 patients had complete response (CR),14 had partial response (PR),and 7 had stable disease (SD),while 8 (25.8%) had progressive disease (PD).The ODC was significantly higher among methylated patients and in those with Ki-67 < 17% (P=0.0003).The median overall TTP was 12 months and the median OS was 20 months for all the patients including those who received Bevacizumab for some stable cases or as a salvage treatment in patients with good PS,the MGMT-methylated patients had a higher median TTP of 13 months (range 8 to 18 months,95% CI of 9.36 to 12.9),and OS of 24 months (range 12 to 31 months,95% CI of 16.1 to 21.32),while the unmethylated patients had a median TTP of 6.5 months and a median OS of 12 months,such correlations were highly significant (P=0.0001).MGMT immunoexpression failed to show significant correlation with MGMT promotor methylation or the outcome of the patients.Patients with Ki-67 < 17% had a median TTP of 16 months and median OS of 24 months compared to 7 and 12.5 months respectively for the patients with Ki-67 ≥17%.Significant correlation was found between the ODC,TTP,and OS with age < 52,near total excision,and TMZ doses received ≥ 10.The commonest grade 3 and 4 toxicities was neutropenia recorded in 3 patients (9.67%),thrombocytopenia in 4 patients (12.9%),and one patient with G3 nausea,vomiting,and constipations (3%),all were medically manageable.Conclusion:MGMT promotor methylation status and Ki-67 LI (but not the MGMT protein expression),could serve as prognostic markers for survival,also MGMT could identify the newly diagnosed GBM patients who will have better response to TMZ.
文摘目的 探讨外周血单核细胞DNA甲基化转移酶1(DNMT1)及血清白介素-6(IL-6)在糖尿病肾脏病(DKD)中的表达及临床意义。方法 选取150例DKD患者(DKD组)及50例同期健康体检者(对照组)。比较2组IL-6、DNMT1、总胆固醇、三酰甘油、高密度脂蛋白胆固醇(HDL-C)、低密度脂蛋白胆固醇(LDL-C)、血肌酐、空腹血糖、肾小球滤过率估计值(e GFR)、24 h尿白蛋白排泄率(24 h UAER)的差异。Pearson相关分析IL-6、DNMT1与其他临床指标的相关性。多因素Logistic回归分析DKD发生的影响因素。受试者工作特征(ROC)曲线分析24 h UAER、IL-6、DNMT1及联合检测对DKD的诊断价值。结果 与对照组比较,DKD组的空腹血糖、IL-6、DNMT1、血肌酐、24 h UAER、LDL-C、糖化血红蛋白水平升高,而eGFR、HDL-C水平降低(均P<0.05)。DKD组的IL-6与DNMT1呈正相关(r=0.560,P<0.05);且IL-6、DNMT1与24 h UAER呈正相关(r分别为0.551和0.570,P<0.05)。24 h UAER、IL-6及DNMT1升高是影响DKD发生的独立危险因素(P<0.05)。24 h UAER、IL-6、DNMT1联合检测诊断DKD的曲线下面积优于单一指标检测。结论 DKD患者DNMT1、IL-6水平升高,24 h UAER、DNMT1、IL-6联合检测可作为临床诊断DKD的良好指标。
文摘The limited regenerative capacity of neuronal cells requires tight orchestration of cell death and survival regulation in the context of longevity, age-associated diseases as well as during the development of the nervous system. Subordinate to genetic networks epigenetic mechanisms like DNA methylation and histone modifications are involved in the regulation of neuronal development, function and aging. DNA methylation by DNA methyltransferases （DNMTs）, mostly correlated with gene silencing, is a dynamic and reversible process. In addition to their canonical actions performing cytosine methylation, DNMTs influence gene expression by interactions with histone modifying enzymes or complexes increasing the complexity of epigenetic transcriptional networks. DNMTs are expressed in neuronal progenitors, post-mi- totic as well as adult neurons. In this review, we discuss the role and mode of actions of DNMTs including downstream networks in the regulation of neuronal survival in the developing and aging nervous system and its relevance for associated disorders.
