Gene induction and apoptosis in human hepatocellular carci-noma cells SMMC-7721 exposed to 5-aza-2'-deoxycytidine.
BACKGROUND
Aberrant DNA methylation plays a key role in human carcinogenesis. 5-aza-2'-deoxycytidine inhibits DNA methylation and induces the expression of genes putatively silenced by promoter methylation in vitro. There are few studies of the biological and clinical significance of 5-aza-2'-deoxycytidine in human hepatocellular carcinoma. This study explored the mechanism of 5-aza-2'-deoxycytidine targeting transcriptional repressor complexes affecting global gene expression in hepatocellular carcinoma cell line.


METHODS
High density oligonucleotide gene expression microarrays were used to examine the effects of 5-aza-2'-deoxycytidine treatments on human hepatocellular carcinoma cell line SMMC-7721. The 5' ends of the genes upregulated or downregulated in this manner were compared with BLAST database to determine whether they might have promoter CpG islands. Flow cytometry was used to detect stages of the cell cycle and apoptosis of SMMC-7721 after being treated with 5-aza-2'-deoxycytidine.


RESULTS
Data obtained 3 days after 4 days of treatment with 5-aza-2'-deoxycytidine showed that more genes were induced in tumorigenic cells including genes that function in cell proliferation, differentiation, regulation of transcription, and cytokine signalling. Approximately 30% of induced genes did not have CpG islands within their 5' regions, suggesting that some genes activated by 5-aza-2'-deoxycytidine may not result from the direct inhibition of promoter methylation. This phenomenon may contribute to a number of upregulated genes involving regulation of transcription in the treated cell. Results showed that 100 micromol/L 5-aza-2'-deoxycytidine blocked cell cycle at S/G2-M phase increasing rate of apoptosis. Notably, we found differential expression of molecular action in the methylation although DNA methyltransferases did not show significant difference in the treated cell line.


CONCLUSIONS
5-aza-2'-deoxycytidine could restore some silenced genes expression independently of DNA methylation inhibition and expression of DNA methyltransferases.
Fan
Hong
H
Key Laboratory of Developmental Genes and Human Disease, Ministry of Education, Southeast University, Nanjing, China. fanh@seu.edu.cn
Zhao
Zhu-Jiang
ZJ
Cheng
Yu-Chao
YC
Shan
Yun-Feng
YF
Lu
Zhu-Hong
ZH
Zhang
Jian-Qiong
JQ
Xie
Wei
W
D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001374:Azacitidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D018899:CpG Islands; D015254:DNA Modification Methylases / Q000235:genetics; D000077209:Decitabine; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D008113:Liver Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D015533:Transcriptional Activation
D000964:Antimetabolites, Antineoplastic; D000077209:Decitabine; D015254:DNA Modification Methylases; D001374:Azacitidine