Deregulation of both imprinted and expressed alleles of the insulin–like growth factor 2 gene during β–cell tumorigenesis

Abstract

In a mouse model of multistage carcinogenesis elicited by the SV40 large T-antigen (Tag) oncogene in pancreatic beta cells, the gene for insulin-like growth factor IGF2 is focally up-regulated and functionally implicated in tumour development. The IGF2 gene is differentially regulated in normal tissues: the paternal allele is transiently expressed during embryogenesis, whereas the maternal allele is genomically imprinted and inactive. Crossbred mice carrying the Tag oncogene and a disruption of either the paternal or maternal allele of IGF2 reveal that both alleles are co-activated early during tumour development, and that each contributes to malignant hyperproliferation and consequent tumour volume.

Reactivation of the maternally imprinted IGF2 allele in TGFα induced hepatocellular carcinomas in mice

“…Therefore, reexpression of all three imprinted IGF2 promoters occurs predominantly but is not universal. All three of the alternatively spliced mRNA's contained the entire IGF2 ORF and should be functional for translation RT ± PCR was performed using the coding sequence primers reported by Christofori et al (1995). This assay also detected speci®c IGF2 mRNA transcripts in tumors with one (Group 4) or two (Group 3) functional IGF2 alleles (Figure 3a).…”

“…All tumors under 0.1 g were ®xed in formalin for histological analysis, the remaining tumors were split and either frozen for RNA/protein analysis or ®xed in formalin for histological analysis. Figure 3 (a) Detection of IGF2 mRNA using the semiquantitations RT ± PCR method of (Christofori et al, 1995). (b) Western blot detection of IGF2, from tumors bearing either two WT IGF2 alleles (TGFa tumor tissue) or one maternal WT IGF2 allele plus one paternal knockout allele (TGFa IGF2 knockout tumor tissue) BMI is a control mRNA from the B 2 Microglobulin gene IFG2 RNA isolation and transcript analysis RNA was extracted from the frozen tissue by a modi®cation of the protocol of Chomczynski and Sacchi (1987).…”

“…The products were run on an Ethidium bromide stained agarose gel, and photographed. Semi-quantitative reverse transcription PCR was performed by the method described by Christofori et al (1995) except that instead of utilizing a-32 P-labeled dATP in the PCR reaction, the PCR reaction was carried out using end labeled 5' oligos. The primers used were b 2 -microglobulin: 5'-GCTATCCAGAAGAAACCCCTCAAATTC; 3'-CA-TGTCTCGATCCCAGTAGACGGTC and IGF2: 5'-CT-TCTACTTCAGCAGGCCTTC; 3'-GTATCTGGGGAAGT-CGTCCGG.…”

“…It has been proposed that IGF2 could be a critical growth factor, a ecting the total number of tumors formed and their rate of growth (Fu et al, 1988;Yang et al, 1996;Schirmacher et al, 1992;Christofori et al, 1994). Christofori et al (1995) observed that endogenous IGF2 gene expression was activated in precancerous lesions and islet cell carcinomas of the pancreas in transgenic mice which express SV40 large T-antigen under regulation of the rat insulin promoter. To test the hypothesis that IGF2 had a functional role in the development of pancreatic tumors, SV40 T-antigen transgenic mice were crossed with transgenic mice containing an IGF2 gene knockout (De Chiara et al, 1990;Christofori et al, 1995).…”

“…Christofori et al (1995) observed that endogenous IGF2 gene expression was activated in precancerous lesions and islet cell carcinomas of the pancreas in transgenic mice which express SV40 large T-antigen under regulation of the rat insulin promoter. To test the hypothesis that IGF2 had a functional role in the development of pancreatic tumors, SV40 T-antigen transgenic mice were crossed with transgenic mice containing an IGF2 gene knockout (De Chiara et al, 1990;Christofori et al, 1995). When tumors formed in the animals, a direct correlation was observed between the number of functional IGF2 genes (1 or 2) and the volume of tumors formed in the pancreas.…”