The novel RASSF6 and RASSF10 candidate tumour suppressor genes are frequently epigenetically inactivated in childhood leukaemias.
BACKGROUND
The Ras-association family (RASSF) of tumour suppressor genes (TSGs) contains 10 members that encode proteins containing Ras-association (RA) domains. Several members of the RASSF family are frequently epigenetically inactivated in cancer, however, their role in leukaemia has remained largely uninvestigated. Also, RASSF10 is a predicted gene yet to be experimentally verified. Here we cloned, characterised and demonstrated expression of RASSF10 in normal human bone marrow. We also determined the methylation status of CpG islands associated with RASSF1-10 in a series of childhood acute lymphocytic leukaemias (ALL) and normal blood and bone marrow samples.


RESULTS
COBRA and bisulphite sequencing revealed RASSF6 and RASSF10 were the only RASSF members with a high frequency of leukaemia-specific methylation. RASSF6 was methylated in 94% (48/51) B-ALL and 41% (12/29) T-ALL, whilst RASSF10 was methylated in 16% (8/51) B-ALL and 88% (23/26) T-ALL. RASSF6 and RASSF10 expression inversely correlated with methylation which was restored by treatment with 5-aza-2'deoxycytidine (5azaDC).


CONCLUSIONS
This study shows the hypermethylation profile of RASSF genes in leukaemias is distinct from that of solid tumours and represents the first report of inactivation of RASSF6 or RASSF10 in cancer. These data show epigenetic inactivation of the candidate TSGs RASSF6 and RASSF10 is an extremely frequent event in the pathogenesis of childhood leukaemia. This study also warrants further investigation of the newly identified RASSF member RASSF10 and its potential role in leukaemia.
Hesson
Luke B
LB
Department of Medical and Molecular Genetics, Institute of Biomedical Research, Medical School, University of Birmingham, Edgbaston, B15 2TT, UK. l.hesson@unsw.edu.au
Dunwell
Thomas L
TL
Cooper
Wendy N
WN
Catchpoole
Daniel
D
Brini
Anna T
AT
Chiaramonte
Raffaella
R
Griffiths
Mike
M
Chalmers
Andrew D
AD
Maher
Eamonn R
ER
Latif
Farida
F
D000595:Amino Acid Sequence; D051017:Apoptosis Regulatory Proteins; D045744:Cell Line, Tumor; D018899:CpG Islands; D019175:DNA Methylation; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D016147:Genes, Tumor Suppressor; D006801:Humans; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics*; D016133:Polymerase Chain Reaction; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000235:genetics*; D016415:Sequence Alignment
D051017:Apoptosis Regulatory Proteins; C519911:RASSF6 protein, human; D020559:Monomeric GTP-Binding Proteins