Regulation of IGF2 transcript and protein expression by altered methylation in breast cancer.
OBJECTIVE
Breast Cancer is one of the leading causes of cancer deaths among women worldwide. The role of epigenetics as a distinct mechanism to alter gene expression in a tissue-specific manner has emerged as an important mechanism in the pathophysiology of cancer. Present study was carried out to assess the role of methylation in regulating transcription and protein expression of Insulin-like growth factor 2 (IGF2), an oncogene with parental imprinting.


METHODS
Paraffin-embedded archival breast tumor and adjacent normal tissue samples were used for carrying out PCR-based methylation assay, genomic PCR, immunohistochemistry and Real-Time Reverse transcriptase PCR.


RESULTS
A significant loss of methylation in exon 9 CpG cluster of IGF2 in breast tumor tissues was observed when compared to normal tissue (P < 0.0001). Expression of IGF2 by immunohistochemistry exhibited a mean twofold increase correlating with the hypomethylation of this specific CpG. Real-Time RT PCR showed increased transcripts in the tumor tissue supporting the IHC and methylation results. A total of 33% of tumor samples heterozygous for the ApaI IGF2 polymorphism exhibited biallelic IGF2 expression due to loss of imprinting; this was not seen in any of the normal breast tissues.


CONCLUSIONS
Altered methylation of exonic CpG plays an important role in the enhanced transcription/expression of IGF2 in breast tumors. Methylation analysis of exon 9 CpG can be used as a biomarker for upregulation of IGF2 in breast tumor tissue and maybe developed as a diagnostic test in future.
Shetty
Preetha J
PJ
Department of Genetics, Vasavi Medical & Research Centre, Khairatabad, Hyderabad 500004, India.
Movva
Sireesha
S
Pasupuleti
Nagarjuna
N
Vedicherlla
Bhavani
B
Vattam
Kiran K
KK
Venkatasubramanian
Sambasivan
S
Ahuja
Yog R
YR
Hasan
Qurratulain
Q
D014408:Biomarkers, Tumor / Q000235:genetics; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D018899:CpG Islands; D019175:DNA Methylation; D005091:Exons; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D018392:Genomic Imprinting; D006801:Humans; D007335:Insulin-Like Growth Factor II / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic; D015854:Up-Regulation
D014408:Biomarkers, Tumor; D007335:Insulin-Like Growth Factor II