Frequent silencing of the candidate tumor suppressor PCDH20 by epigenetic mechanism in non-small-cell lung cancers.
Protocadherins are a major subfamily of the cadherin superfamily, but little is known about their functions and intracellular signal transduction. We identified a homozygous loss of protocadherin 20 (PCDH20, 13q21.2) in the course of a program to screen a panel of non-small-cell lung cancer (NSCLC) cell lines (1 of 20 lines) for genomic copy number aberrations using an in-house array-based comparative genomic hybridization. PCDH20 mRNA was expressed in normal lung tissue but was not expressed in the majority of NSCLC cell lines without a homozygous deletion of this gene (10 of 19 lines, 52.6%). Expression of PCDH20 mRNA was restored in gene-silenced NSCLC cells after treatment with 5-aza 2'-deoxycytidine. The DNA methylation status of the PCDH20 CpG-rich region correlated inversely with the expression of the gene and a putative target region for methylation showed clear promoter activity in vitro. Methylation of this PCDH20 promoter was frequently observed in primary NSCLC tissues (32 of 59 tumors, 54.2%). Among our primary NSCLC cases, the methylated PCDH20 seemed to be associated with a shorter overall survival (P = 0.0140 and 0.0211 in all and stage I tumors, respectively; log-rank test), and a multivariate analysis showed that the PCDH20 methylation status was an independent prognosticator. Moreover, restoration of PCDH20 expression in NSCLC cells reduced cell numbers in colony formation and anchorage-independent assays. These results suggest that epigenetic silencing by hypermethylation of the CpG-rich promoter region of PCDH20 leads to loss of PCDH20 function, which may be a factor in the carcinogenesis of NSCLC.
Imoto
Issei
I
Department of Molecular Cytogenetics, Medical Research Institute and Graduate School of Biomedical Science, Tokyo Medical and Dental University, Tokyo, Japan.
Izumi
Hiroyuki
H
Yokoi
Sana
S
Hosoda
Hiroshi
H
Shibata
Tatsuhiro
T
Hosoda
Fumie
F
Ohki
Misao
M
Hirohashi
Setsuo
S
Inazawa
Johji
J
D000368:Aged; D015820:Cadherins / Q000235:genetics*; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics* / Q000473:pathology; D048708:Cell Growth Processes / Q000235:genetics; D045744:Cell Line, Tumor; D018899:CpG Islands; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D005260:Female; D017353:Gene Deletion; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D018390:Gene Targeting; D016147:Genes, Tumor Suppressor; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009693:Nucleic Acid Hybridization; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics
D015820:Cadherins; D012333:RNA, Messenger