The anti-aging gene KLOTHO is a novel target for epigenetic silencing in human cervical carcinoma.
BACKGROUND
Klotho was originally characterized as an anti-aging gene that predisposed Klotho-deficient mice to a premature aging-like syndrome. Recently, KLOTHO was reported to function as a secreted Wnt antagonist and as a tumor suppressor. Epigenetic gene silencing of secreted Wnt antagonists is considered a common event in a wide range of human malignancies. Abnormal activation of the canonical Wnt pathway due to epigenetic deregulation of Wnt antagonists is thought to play a crucial role in cervical tumorigenesis. In this study, we examined epigenetic silencing of KLOTHO in human cervical carcinoma.


RESULTS
Loss of KLOTHO mRNA was observed in several cervical cancer cell lines and in invasive carcinoma samples, but not during the early, preinvasive phase of primary cervical tumorigenesis. KLOTHO mRNA was restored after treatment with either the DNA demethylating agent 2'-deoxy-5-azacytidine or histone deacetylase inhibitor trichostatin A. Methylation-specific PCR and bisulfite genomic sequencing analysis of the promoter region of KLOTHO revealed CpG hypermethylation in non-KLOTHO-expressing cervical cancer cell lines and in 41% (9/22) of invasive carcinoma cases. Histone deacetylation was also found to be the major epigenetic silencing mechanism for KLOTHO in the SiHa cell line. Ectopic expression of the secreted form of KLOTHO restored anti-Wnt signaling and anti-clonogenic activity in the CaSki cell line including decreased active beta-catenin levels, suppression of T-cell factor/beta-catenin target genes, such as c-MYC and CCND1, and inhibition of colony growth.


CONCLUSIONS
Epigenetic silencing of KLOTHO may occur during the late phase of cervical tumorigenesis, and consequent functional loss of KLOTHO as the secreted Wnt antagonist may contribute to aberrant activation of the canonical Wnt pathway in cervical carcinoma.
Lee
Jaehyouk
J
Research Center for Women's Diseases and Division of Biological Science, Sookmyung Women's University, Seoul 140-742, Republic of Korea.
Jeong
Dong-Jun
DJ
Kim
Jinsun
J
Lee
Soonduck
S
Park
Jin-Hwa
JH
Chang
Boogi
B
Jung
Sam-Il
SI
Yi
Lisha
L
Han
Youngsoo
Y
Yang
Young
Y
Kim
Keun Il
KI
Lim
Jong-Seok
JS
Yang
Inchul
I
Jeon
Seob
S
Bae
Dong Han
DH
Kim
Chang-Jin
CJ
Lee
Myeong-Sok
MS
D047369:Chromatin Immunoprecipitation; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation; D005260:Female; D015870:Gene Expression; D020869:Gene Expression Profiling; D020868:Gene Silencing; D005966:Glucuronidase / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D000090265:Klotho Proteins; D011401:Promoter Regions, Genetic / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D002583:Uterine Cervical Neoplasms / Q000235:genetics* / Q000378:metabolism; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism
D051153:Wnt Proteins; D005966:Glucuronidase; D000090265:Klotho Proteins