Novel splicing of an IGF2 polymorphic region in human adrenocortical carcinomas

The human IGF2 gene lies on chromosome 11p15.5 and encodes for a mitogenic peptide. IGF2 is often overexpressed in many tumours including adrenal carcinomas. In this study while screening 12 adrenocortical carcinomas for heterozygosity at the Apa I and (CA)n repeat polymorphisms we observed a novel splicing event in two samples which showed both an allelic expression imbalance and preferential splicing for one of the alleles. Further examination revealed that the splicing was not confined to one particular site. Three of such splice products were isolated and cloned. Using RNase protection analysis the presence of this splicing event was demonstrated for both adrenocortical carcinoma samples and also in a Hep3B cell line. This suggested that the event may be occurring in all the samples. The presence of this splicing was then confirmed in all 12 adrenocortical carcinoma samples by PCR. These data suggest that the splicing event may be a general feature for IGF2 transcripts.