Promoter-independent loss of mRNA and protein of the Rb gene in a human hepatocellular carcinoma.
BACKGROUND
Inactivation of the retinoblastoma (Rb) gene is considered to play a fundamental role in the genesis and progression of several human cancers. In retinoblastoma, the inactivation of Rb promoter by mutations or hypermethylation has been reported. Although genetic changes of Rb gene have been described in hepatocellular carcinoma (HCC), an epigenetic change such as hypermethylation of the Rb promoter as reported in retinoblastoma has not been described.


METHODS
We examined the hypermethylation in the promoter region of Rb gene by restriction fragment length polymorphism in 19 HCCs, as well as the expression of Rb mRNA and protein by RT-PCR and by immunoblotting, respectively.


RESULTS
We found no evidence of hypermethylation in the promoter region of the Rb gene in all HCCs analyzed. However, the expression of Rb mRNA and protein was lost in one HCC, and no mutation was detected in the Rb promoter region of this patient. The inactivation of Rb promoter by hypermethylation or by inhibition of binding of transcription factors due to point mutations did not contribute to the loss of mRNA and protein in the patient.


CONCLUSIONS
Hypermethylation in the Rb promoter region appeared to have little causal effect on HCC.
Hada
H
H
First Department of Internal Medicine, Okayama University Medical School.
Koide
N
N
Morita
T
T
Shiraha
H
H
Shinji
T
T
Nakamura
M
M
Ujike
K
K
Takayama
N
N
Oka
T
T
Hanafusa
T
T
Yumoto
Y
Y
Hamazaki
K
K
Tsuji
T
T
D000368:Aged; D006528:Carcinoma, Hepatocellular / Q000235:genetics* / Q000473:pathology; D005260:Female; D015870:Gene Expression; D016161:Genes, Retinoblastoma / Q000235:genetics*; D006801:Humans; D015151:Immunoblotting; D008113:Liver Neoplasms / Q000235:genetics* / Q000473:pathology; D008297:Male; D008745:Methylation; D008875:Middle Aged; D010766:Phosphorylation; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D012333:RNA, Messenger / Q000235:genetics*; D012194:RNA-Directed DNA Polymerase
D012333:RNA, Messenger; D012194:RNA-Directed DNA Polymerase