Hypermethylation of a small CpGuanine-rich region correlates with loss of activator protein-2alpha expression during progression of breast cancer.
The transcription factor activator protein-2alpha (AP-2alpha) has recently been implicated as a tumor suppressor protein that can be lost during tumor progression and that exhibits growth-inhibitory properties when overexpressed in cancer cell lines. We now demonstrate that hypermethylation of a discrete 5' region within a promoter CpG island of the gene is associated in breast cancer with the loss of AP-2alpha expression. Multiple CpG sites within the island become hypermethylated during breast cancer evolution. However, only hypermethylation of the most CpG-rich region, a small, approximately 300-bp area at the 3' end of exon 1, fully distinguishes neoplastic from normal breast tissue and correlates with transcriptional silencing. In cell culture, silenced AP-2alpha, associated with exon 1 hypermethylation, is re-expressed by 5-aza-2'deoxycytidine resulting in the restoration of a functional DNA sequence-specific binding protein. In vivo, as detected by a very sensitive nested PCR approach, methylation of the discrete AP-2alpha exon 1 region does not occur in normal breast epithelium and occurs in only 3 (16%) of 19 ductal carcinoma in situ (DCIS) lesions, but is present in 12 (75%) of 16 invasive breast tumors (P < 0.001; DCIS versus invasive cancers). Tumors unmethylated for this region expressed AP-2alpha protein throughout, whereas tumors with hypermethylation showed large areas of loss. Our studies then determine that hypermethylation of a small region of a CpG island correlates with silencing of AP-2alpha in breast cancer and suggest that inactivation of this gene could be a factor in, and a useful marker for, the progression of DCIS lesions.
The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Baltimore, MD 21231, USA.
Donna B
DB
Douglas
Yoshimitsu
Y
Akiyama
Hetty
H
Carraway
Steven A
SA
Belinsky
Manel
M
Esteller
Edward
E
Gabrielson
Sigmund
S
Weitzman
Trevor
T
Williams
James G
JG
Herman
Stephen B
SB
Baylin
D001943:Breast Neoplasms / Q000235:genetics*; D002278:Carcinoma in Situ / Q000235:genetics; D018270:Carcinoma, Ductal, Breast / Q000235:genetics; D045744:Cell Line, Tumor; D018899:CpG Islands; D019175:DNA Methylation; D004268:DNA-Binding Proteins / Q000032:analysis / Q000235:genetics* / Q000502:physiology; D018450:Disease Progression; D005091:Exons; D005260:Female; D006801:Humans; D011401:Promoter Regions, Genetic; D050656:Transcription Factor AP-2; D014157:Transcription Factors / Q000032:analysis / Q000235:genetics* / Q000502:physiology
D004268:DNA-Binding Proteins; C493673:TFAP2A protein, human; D050656:Transcription Factor AP-2; D014157:Transcription Factors