Loss of expression of the growth inhibitory gene GADD45gamma, in human pituitary adenomas, is associated with CpG island methylation.
Inappropriate expression of cell-cycle regulatory genes and/or their protein products are a frequent finding in pituitary tumours; however, genetic changes associated with or responsible for their dysregulation are in general uncommon. In a search for novel genes, and employing cDNA-representational difference analysis, the gene encoding GADD45gamma was recently isolated and identified as being under-represented in pituitary adenomas. GADD45gamma is a member of a family of genes that are induced by DNA damage and function in the negative regulation of cell growth. In this study, we further confirm this initial report that the majority of pituitary adenomas (22 of 33; 67%) do not express GADD45gamma as determined by RT-PCR analysis. Loss of expression was not associated with either loss of heterozygosity or mutations within the coding region of this gene. In marked contrast, epigenetic change, namely methylation of the GADD45gamma genes CpG island, was a frequent finding (19 of 33 adenoma; 58%) and was significantly associated with tumours in which GADD45gamma transcript was not expressed (18 of 22; 82%; P=0.002). In common with the primary tumours, methylation-associated gene silencing of the GADD45gamma gene was also found in the pituitary tumour cell line AtT20. The treatment of AtT20 cells with the demethylating agent, 5-Aza-2'-deoxycytidine, induced the re-expression of this gene. These findings show that silencing of the GADD45gamma gene in pituitary tumours is primarily associated with methylation of the genes CpG island. Methylation has functional importance since reversal of this epigenetic change in a pituitary-derived cell line is associated with re-expression. Silencing of GADD45gamma, a negative regulator of cell growth, is most likely responsible for conferring a selective growth advantage during tumour evolution and outgrowth.
Bahar
Adil
A
School of Medicine, Keele University, North Staffordshire Hospital, Stoke-on-Trent, Staffordshire ST4 7QB, UK.
Bicknell
John E
JE
Simpson
David J
DJ
Clayton
Richard N
RN
Farrell
William E
WE
D000236:Adenoma / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D018899:CpG Islands; D019175:DNA Methylation; D017931:DNA Primers; D004273:DNA, Neoplasm; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D019656:Loss of Heterozygosity; D008969:Molecular Sequence Data; D010911:Pituitary Neoplasms / Q000235:genetics* / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011506:Proteins / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000097642:GADD45 Proteins
D017931:DNA Primers; D004273:DNA, Neoplasm; D047908:Intracellular Signaling Peptides and Proteins; D011506:Proteins; D000097642:GADD45 Proteins