The tumor suppressor gene DLEC1 is frequently silenced by DNA methylation in hepatocellular carcinoma and induces G1 arrest in cell cycle.
OBJECTIVE
The chromosome locus 3p21.3 is a "hot-spot" for chromosomal aberrations and loss of heterozygosity in cancers. The 35 genes mapped to the AP20 subregion of this locus were screened for their expression to identify candidate tumor suppressor genes. DLEC1 was selected for further characterization in primary hepatocellular carcinomas and cell lines.


METHODS
RT-PCR and methylation-specific PCR were performed to examine the expression and methylation. Stable clones with DLEC1 overexpression were established to analyze cell proliferation and cell cycle.


RESULTS
DLEC1 was silenced and hypermethylated in 9 of 11 cell lines examined. Treatment with 5-aza-2'-deoxycytidine reversed the methylation and restored DLEC1 expression. The correlation between hypermethylation and expression was also demonstrated in 10 pairs of hepatocellular carcinoma and adjacent normal tissues (t-test, p<0.05). Hypermethylation of DLEC1 was detected in 70.6% of tumors, compared to 10.3% in normal tissues (n=68, p<0.001, chi(2)). Of interest, DLEC1 methylation was associated with the AJCC staging of the tumors (p=0.036, chi(2)). DLEC1 over-expression in cell lines decreased colony formation, cell growth and cell size, and induced a G1 arrest in cell cycle.


CONCLUSIONS
Our data indicate that DLEC1 is a candidate tumor suppressor gene that plays an important role in the development and progression of hepatocellular carcinoma.
Qiu
Guo-Hua
GH
Department of Physiology, Faculty of Medicine, National University of Singapore, Singapore.
Salto-Tellez
Manuel
M
Ross
James A
JA
Yeo
Winnie
W
Cui
Yan
Y
Wheelhouse
Nicholas
N
Chen
George G
GG
Harrison
David
D
Lai
Paul
P
Tao
Qian
Q
Hooi
Shing Chuan
SC
D006528:Carcinoma, Hepatocellular / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002453:Cell Cycle / Q000235:genetics / Q000502:physiology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D048429:Cell Size; D018899:CpG Islands / Q000235:genetics / Q000502:physiology; D019175:DNA Methylation; D004273:DNA, Neoplasm / Q000378:metabolism; D018450:Disease Progression; D005260:Female; D016193:G1 Phase / Q000235:genetics / Q000502:physiology*; D020868:Gene Silencing / Q000502:physiology*; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
C119064:DLEC1 protein, human; D004273:DNA, Neoplasm; D025521:Tumor Suppressor Proteins