Promoter methylation-associated loss of ID4 expression is a marker of tumour recurrence in human breast cancer

Abstract

<p>Abstract</p> <p>Background</p> <p>Inhibitor of DNA binding/Inhibitor of differentiation 4 (<it>ID4</it>) is a critical factor for cell proliferation and differentiation in normal vertebrate development. <it>ID4</it> has regulative functions for differentiation and growth of the developing brain. The role of <it>ID1</it>, <it>ID2</it> and <it>ID3</it> are expected to be oncogenic due to their overexpression in pancreatic cancer and colorectal adenocarcinomas, respectively. Aside from these findings, loss of <it>ID3</it> expression was demonstrated in ovarian cancer. The aim of the present study was to reveal the factual role of <it>ID4</it> in carcinogenesis in more detail, since its role for the pathogenesis of human breast cancer has been discussed controversially, assigning both oncogenic and tumour suppressive functions. </p> <p>Methods</p> <p><it>ID4</it> promoter methylation, <it>ID4</it> mRNA expression and <it>ID4</it> protein expression were analysed in primary human breast cancer specimens using methylation-specific PCR (MSP) (n=170), semiquantitative realtime RT-PCR (n=46) and immunhistochemistry (n=3), respectively. In order to demonstrate a functional association of <it>ID4</it> promoter methylation with its gene silencing, we performed DNA demethylation analysis with four human breast cell lines using MSP and semiquantitative realtime RT-PCR. In addition, we performed correlations of <it>ID4</it> promoter methylation with <it>ID4</it> mRNA and <it>ID4</it> protein expression in matched samples of breast tumour and corresponding normal tissue. We carried out statistical analyses in order to find correlations between <it>ID4</it> promoter methylation and clinicopathological parameters. </p> <p>Results</p> <p>Frequent <it>ID4</it> promoter methylation was observed in primary breast cancer samples (69%, 117/170). We found a tight correlation (P<0.0001) between <it>ID4</it> promoter methylation and loss of <it>ID4</it> expression in primary breast cancer 3 specimens. Demethylating treatment with breast cancer cell lines was associated with clear ID4 mRNA re-expression. Tumours with <it>ID4</it> promoter methylation showed distinct loss of <it>ID4</it> expression on both transcription and protein level. Interestingly, <it>ID4</it> promoter methylation was a factor for unfavourable recurrence-free survival (P=0.036) and increased risk for lymph node metastasis (P=0.030). </p> <p>Conclusion</p> <p>ID4 is indeed a novel tumour suppressor gene in normal human breast tissue and is epigenetically silenced during cancer development, indicating increased risk for tumour relapse. Thus, <it>ID4</it> methylation status could serve as a prognostic biomarker in human breast cancer.</p