Concordant loss of imprinting of the human insulin-like growth factor II gene promoters in cancer

The human insulin-like growth factor II (IGFII) gene has been shown to be imprinted for the promoters P2, P3, and P4 but not for the promoter P1 in liver and chondrocytes. Loss of imprinting of the IGFII gene has been found in a variety of human tumors including rhabdomyosarcoma and lung cancer. In this report, we determined whether loss of imprinting in tumors displays a promoter-specific pattern. We examined allelic expression of all four IGFII promoters in rhabdomyosarcoma, lung cancer, and normal skeletal muscle. We demonstrate that the imprinting of all IGFII promoters is relaxed in rhabdomyosarcoma and lung cancer. These data suggest that loss of imprinting of IGFII gene promoters may be regulated coordinately by a common mechanism in these tumors. Unexpectedly, we also found that P1, in addition to P2, P3, and P4 is monoallelically expressed in three informative adult skeletal muscle tissues. This indicates that imprinting of the IGFII promoter P1 occurs in a tissue-specific manner.