Association of low p16INK4a and p15INK4b mRNAs expression with their CpG islands methylation with human hepatocellular carcinogenesis.
OBJECTIVE
To study the significance of p16 and p15 transcription suppression with hypermethylation of their genes' 5'CpG islands during human hepatocellular carcinogenesis.


METHODS
The mRNA expression levels of p16 and p15 genes were evaluated in cancerous, para-cancerous and non-cancerous tissues of 20 HCC, 3 normal liver tissues from 3 accidentally died healthy adults using semi-quantitatively Northern blot. The methylation status was also assessed with methylation specific PCR.


RESULTS
p16 mRNA expression level was decreased in the cancerous tissues in 60% (12/20) of HCC patients, of which 2 cases had no p16 mRNA detected, 5 cases (25%) displayed variation in the order of cancerous<para-cancerous<non-cancerous liver tissues. p15 mRNA expression level was decreased in the cancerous tissues in 50% (10/20) HCC patients, of which one case had no p15 mRNA detected, 4 cases (20%) displayed variation in the order of cancerous<para-cancerous<non-cancerous liver tissues. In cancerous, para-cancerous and non-cancerous tissues, p16 promoter CpG islands hypermethylation occurred 65%, 60% and 35%, while p15 promoter CpG islands hypermethylation occurred 50%, 40% and 25%. Of 12 HCCs with lower p16 mRNA expression level, 11 cases showed p16 promoter CpG islands methylation (91.6%). Hundred percent (10/10) HCCs with lower p15 mRNA expression level showed p15 promoter CpG islands methylation. Significant correlation between 5'CpG islands methylation and p16/p15 mRNA expression suppression was found. The decreased expression of p16/p15 mRNA or methylation of p16/p15 promoters 5'CpG island was significantly correlate with poor differentiation of HCC (P=0.0083, 0.0102, 0.00271, 0.0218, respectively, P<0.05).


CONCLUSIONS
p16 and p15 genes transcriptional inactivation might play an important role in hepatocarcinogenesis. 5'CpG islands methylation might be the major mechanism of p16 and p15 genes inactivation in primary HCC in the studied population. 5'CpG islands methylation of p16 and p15 genes might be an early event in hepatocarcinogenesis.
Qin
Yang
Y
Department of Biochemistry and Molecular Biology, School of Preclinical and Forensic Medicine, West China Medical Center, Sichuan University, Chengdu, 610041, Sichuan Province, China. qin_1@sina.com
Liu
Jian-Yu
JY
Li
Bo
B
Sun
Zhi-Lin
ZL
Sun
Ze-Fang
ZF
D000328:Adult; D006528:Carcinoma, Hepatocellular / Q000235:genetics* / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics* / Q000378:metabolism; D018899:CpG Islands; D050762:Cyclin-Dependent Kinase Inhibitor p15; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics* / Q000378:metabolism; D019175:DNA Methylation; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism
C493966:CDKN2B protein, human; D018797:Cell Cycle Proteins; D050762:Cyclin-Dependent Kinase Inhibitor p15; D019941:Cyclin-Dependent Kinase Inhibitor p16; D012333:RNA, Messenger; D025521:Tumor Suppressor Proteins