I. Kuzmin et al., Analysis of aberrant methylation of the VHL gene by transgenes, monochromosome transfer, and cell fusion, ONCOGENE, 18(41), 1999, pp. 5672-5679
Several tumor suppressor genes were shown to be inactivated by a process in
volving aberrant de novo methylation of their GC-rich promoters which is us
ually associated with transcriptional repression, The mechanisms underlying
this process are poorly understood. In particular this abnormal methylatio
n may be caused and/or maintained by either deficiency of some tl ails-acti
ng factor(s) or by various malfunctions acting in cis, Here we studied the
nature of aberrant methylation of the ron Hippel-Lindau (VHL) disease tumor
suppressor gene in a human clear cell renal carcinoma cell line, UOK 121,
that contains a silent hypermethylated endogenous VHL allele, First, we tra
nsfected unmethylated VHL transgenes, driven by the VHL promoter, into UOK
121 cells. Next, to exclude possible position effects that may influence me
thylation of the introduced VHL genes, we transferred a single chromosome 3
, carrying an apparently normal hypomethylated VHL allele into the UOK 121
cells. Finally, ne created somatic cell hybrids between UOK 121 and UMRC 6
cells containing a mutant VHL-expressing hypomethylated allele, In these th
ree experiments both the methylation of the VHL promoter and the transcript
ional status of the introduced and endogenous VHL alleles remained unchange
d. Our results demonstrate that the putative tr ans-acting factors present
in the UOK 121 and UMRC 6 cells are unable to induce changes in methylation
pattern of the VHL alleles in all cell lines and hybrids studied. Taken to
gether, the results indicate that ris-specific local features are pivotal i
n maintaining and perpetuating aberrant methylation of the VHL CpG island.
Contribution of some putative tr ans-acting factors cannot be excluded duri
ng a period when the aberrant VHL methylation pattern was first generated.