Aberrant methylation and reduced expression of RASSF1A in Ewing sarcoma.
BACKGROUND
Ewing sarcoma (ES) is the second most common solid bone and soft tissue malignancy in children and young adults with low cure rates indicating the need to identify further prognostic markers. The importance of methylation in the inactivation of key tumor suppressor genes including RASSF1A has begun to be appreciated in context of cancer development, prognosis and therapy. However there is lack of similar broad based studies in ES. The objective of this study was to analyze RASSF1A methylation and assess its clinical significance in ES.


METHODS
The methylation of RASSF1A was determined 31 ES tumor samples and 4 ES cell lines. ES cell lines were also treated with demethylating agent 5-aza-2'-deoxycytidine to ascertain its effect on methylation. RASSF1A expression was studied in 12 ES tumors. The association between RASSF1A methylation, clinical parameters and outcome was also analyzed.


RESULTS
Methylation of RASSF1A was observed in 21/31 (68%) tumors and in 3/4 ES cell lines. A significant correlation of methylation to reduced expression of RASSF1A was observed in 12 ES tumors analyzed (P = 0.0013) and in all cell lines. ES patients with methylated RASSF1A had worse prognosis compared to the unmethylated group (P = 0.049). Treatment with 5-aza-2'-deoxycytidine resulted in the re-expression of the unmethylated form of RASSF1A in two ES cell lines.


CONCLUSIONS
RASSF1A is frequently methylated in ES.
Avigad
Smadar
S
Molecular Oncology, Felsenstein Medical Research Center, Petah Tikva, Israel. savigad@post.tau.ac.il
Shukla
Shruti
S
Naumov
Inna
I
Cohen
Ian J
IJ
Ash
Shifra
S
Meller
Isaac
I
Kollender
Yehuda
Y
Issakov
Josephine
J
Yaniv
Isaac
I
D045744:Cell Line, Tumor; D002648:Child; D019175:DNA Methylation; D020868:Gene Silencing; D006801:Humans; D012512:Sarcoma, Ewing / Q000235:genetics*; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism
C411762:RASSF1 protein, human; D025521:Tumor Suppressor Proteins