Decreased expression of insulin-like growth factor binding protein 7 in human colorectal carcinoma is related to DNA methylation.
OBJECTIVE
Insulin-like growth factor binding protein 7 (IGFBP-7) is considered a tumor suppressor in various cancers, but its role in colorectal cancer (CRC) is still uncertain. The aims of this study were to analyze the IGFBP-7 expression, and explore the mechanism responsible for the inactivation of IGFBP-7 in CRC.


METHODS
mRNA expression was studied by RT-PCR and Northern blot analysis of cultured cells. Methylation status was analyzed by treatment with 5-aza-2'-deoxycytidine followed by sequencing of PCR products of sodium bisulfite-treated genomic DNA. IGFBP-7 protein expression was evaluated by immunohistochemistry (IHC) on tissue microarrays.


RESULTS
mRNA expression was lost in six out of eight CRC cell lines as compared to normal colon cells. DNA methylation was found in the region of exon 1 and intron 1 of IGFBP-7. In tumor tissue, 107 out of 279 samples showed a negative expression of IGFBP-7 by IHC, which was significantly associated with poor prognosis. The analysis of 37 paired cancerous and normal mucosa samples confirmed the downregulation in the tumors, but revealed variable basal expression levels of IGFBP-7 in normal mucosal samples.


CONCLUSIONS
DNA methylation is a mechanism responsible for IGFBP-7 gene silencing providing a target for therapeutic intervention of this tumor suppressor gene.
Ye
Fei
F
Institute of Pathology, Charité University Medicine Berlin-Campus Mitte, 10098 Berlin, Germany.
Chen
Yuan
Y
Knösel
Thomas
T
Schlüns
Karsten
K
Pacyna-Gengelbach
Manuela
M
Deutschmann
Nicole
N
Lai
Maode
M
Petersen
Iver
I
D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000378:metabolism; D019175:DNA Methylation; D015870:Gene Expression; D015972:Gene Expression Regulation, Neoplastic; D016147:Genes, Tumor Suppressor; D006801:Humans; D007150:Immunohistochemistry; D018969:Insulin-Like Growth Factor Binding Proteins / Q000235:genetics* / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017384:Sequence Deletion
D018969:Insulin-Like Growth Factor Binding Proteins; D012333:RNA, Messenger; C102529:insulin-like growth factor binding protein-related protein 1