Human Molecular Genetics!!!

Somatically Acquired Hypomethylation of IGF2 in Breast and Colorectal Cancer

Yoko Ito, Thibaud Koessler, Ashraf E.K. Ibrahim, Sushma Rai, Sarah L. Vowler, Sayeda Abu-Amero, Ana-Luisa Silva, Ana-Teresa Maia, Joanna E. Huddleston, Santiago Uribe-Lewis, Kathryn Woodfine, Maja Jagodic, Raffaella Nativio, Alison Dunning, Gudrun Moore, Elena Klenova, Sheila Bingham, Paul D.P. Pharoah, James D. Brenton, Stephan Beck, Manjinder S. Sandhu and Adele Murrell,

Received April 9, 2008; Revised May 21, 2008; Accepted May 23, 2008

The imprinted Insulin-like growth factor 2 gene (IGF2) is expressed predominantly from the paternal allele. Loss of imprinting (LOI) associated with hypomethylation at the promoter proximal sequence (DMR0) of the IGF2 gene was proposed as a predisposing constitutive risk biomarker for colorectal cancer. We used pyrosequencing to assess whether IGF2 DMR0 methylation is either present constitutively prior to cancer or whether it is acquired tissue-specifically after the onset of cancer. DNA samples from tumour tissues and matched non-tumour tissues from 22 breast and 42 colorectal cancer patients as well as peripheral blood samples obtained from Colorectal cancer patients (SEARCH (n= case 192, controls 96)), breast cancer patients (ABC (n= case 364, controls 96)) and the European Prospective Investigation of Cancer (EPIC-Norfolk (n=breast 228, colorectal 225, controls 895)), were analysed. The EPIC samples were collected two to five years prior to diagnosis of breast or colorectal cancer. IGF2 DMR0 methylation levels in tumours were lower than matched non-tumour tissue. Hypomethylation of DMR0 was detected in breast (33%) and colorectal (80%) tumour tissues with a higher frequency than LOI indicating that methylation levels are a better indicator of cancer than LOI. In the EPIC population the prevalence of IGF2 DMR0 hypomethylation was 9.5% and this correlated with increased age not cancer risk. Thus IGF2 DMR0 hypomethylation occurs as an acquired tissue-specific somatic event rather than a constitutive innate epimutation. These results indicate that IGF2 DMR0 hypomethylation has diagnostic potential for colon cancer rather than value as a surrogate biomarker for constitutive LOI.