Elevated Expression of the Stem Cell Marker CD133 Associated with Line-1 Demethylation in Hepatocellular Carcinoma

The relationship of Line-1 demethylation and the CD133 expression of cancer stem cells were discussed in hepatocellular carcinoma (HCC).

In 95 HCC and matched nontumor tissues, we analyzed the methylation level of Line-1 by quantitative real-time methylation-specific polymerase chain reaction, and the expression of CD133 by real-time reverse transcriptase–polymerase chain reaction and immunohistochemistry.

Unmethylation of Line-1 increased from nontumor tissues (1.23 × 10⁷ copies/μg DNA) toward HCC tissues (2.99 × 10⁷ copies/μg DNA), but methylation of Line-1 kept 2 × 10⁸ copies/μg DNA around in HCC and nontumor tissues. The methylation index (MI) of Line-1 decreased from 0.919 in nontumor samples to 0.755 in HCC. Results showed that cumulative survival was significantly shorter in HCC patients with MI < 0.76 than that in patients with MI ≥ 0.76. CD133 mRNA expression were higher in HCC tissues (mean −∆_Ct = −5.751) than that in nontumor tissues (mean −∆_Ct = −6.742). A total of 73 (76.8%) patients had demethylation of Line-1 (∆MI < 0), and 22 (23.2%) patients had hypermethylation of Line-1 (∆MI ≥ 0). HCC with demethylation of Line-1 had elevated CD133 expression in tumor rather than matched nontumor tissues (mean −∆_∆Ct = 1.101), but HCC with hypermethylation of Line-1 was considered to be lower with CD133 expression in tumor (mean −∆_∆Ct = −0.409).

Line-1 hypomethylation is the most common molecular abnormality during the carcinogenic process. Elevated expression of CD133 was associated with demethylation of Line-1 in HCC.