Abstract
It is accepted that cancer progression is a multi-step process including multiple
genetic and epigenetic events. In this study, two sets of candidate genes in colon and
lung cancer tumourigenesis were studied. The first set comprised members of a
family of genes whose proteins are important in the recognition of the
methylation/epigenetic status of other genes. The second set were members of a
pathway that normally regulate tissue development but whose abnormal, epigenetic
loss of activity could lead to tissue dysregulation and tumourigenesis.
MBD3 and MBD2 are two members of the MBD family of proteins with a methyl-
CpG-binding domain (MBD) involved in transcriptional silencing of methylated
genes. Both genes are located in chromosomal regions that suffer loss of
heterozygosity in colon and lung cancers. By SSCP analysis and methylation
sensitive restriction followed by PCR, 2 mutations were found in 28 cell lines and in
no cases was there evidence of gene silencing by hypermethylation of putative
promoter regions. RT-PCR and northern hybridisation showed expression of MBD3
in all cancer cell lines examined. The results indicate that neither MBD2 nor MBD3
are major targets of genetic and epigenetic alteration in colon and lung cancers.
The Hedgehog (Hh) pathway is a highly conserved signaling cascade involved in
many developmental processes. Mutations in elements of the pathway are associated
with congenital diseases and a number of neoplasms. In this study, two genes of this
pathway, SMO and GLI3 were investigated for expression and epigenetic alterations
in colon and lung cancers. In three cell lines expression of SMO was absent, the
putative SMO promoter was fully methylated and GLI3 was not expressed. Two
other cell lines had a methylated wild-type SMO allele and expressed mutant SMO,and also did not express GLI3. The results indicate that SMO is silenced by CpG
island hypermethylation in colon and lung cancer cell lines, that GLI3 is also
silenced in colon and lung cancer cell lines by an as yet unrevealed mechanism and
that GLI3 is possibly regulated by SMO in a manner outside the normal sequence of
steps currently thought to comprise the Hh pathway.
