Loss of imprinting of the insulin-like growth factor II gene in mouse hepatocellular carcinoma cell lines

We investigated expression of insulin-like growth factor II (Igf2) in primary cultured hepatocytes, liver epithelial (LE) cell lines derived from normal hepatocytes, and hepatocellular carcinoma (HCC) cell lines from crosses between C3H/HeJ (C3H) and Mus musculus molossinus mice (MSM). Igf2 mRNA was detected by reverse transcriptase-polymerase chain reaction in primary cultured hepatocytes from 5 d after the start of cultivation and in all 12 LE and 16 HCC cell lines. Analysis of the untranslated region of Igf2 exon 6, which contains polymorphic CA repeats, revealed that 13 of the 16 HCC cell lines had biallelic expression, whereas monoallelic expression was retained in the primary cultured hepatocytes and all 12 LE cell lines. The Igf2 transcripts contained exons 1-3 in all the HCC cell lines but only exons 2 and 3 in cultures of hepatocytes and LE cell lines, indicating difference in promoter use. However, the biallelic HCC cell lines did not have larger amounts of Igf2 mRNA and protein than did the monoallelic lines, suggesting that loss of imprinting may not be directly related to the level of Igf2 expression. (C) 1998 Wiley-Liss, Inc.