Increased expression of insulin-like growth factor 2 in hepatocellular carcinoma is primarily regulated at the transcriptional level.

To investigate the control mechanisms of insulin-like growth factor 2 (IGF2) gene expression, we studied 25 hepatocellular carcinomas (HCC) to compare the levels of total IGF2 mRNA and the IGF2 peptide by using in situ hybridization and immunohistochemistry, respectively. Increased expression of IGF2 mRNA and the IGF2 peptide was observed in 13 HCC. The spatial distribution and intensity of IGF2 mRNA in these 13 HCC was almost identical to that of the IGF2 peptide, which suggests that high IGF2 expression was primarily regulated at the transcriptional level. The levels of IGF2 gene expression in the 13 HCC seemed to be inversely correlated with the degree of tumor cell differentiation. Furthermore, in situ hybridization using probes specific to transcripts expressed from the IGF2 promoters P1 and P3 revealed that transcription was predominantly from P3 rather than from P1.