Expression of insulin-like growth factor II (IGF-II) in human primary liver cancer: mRNA and protein analysis. 
Insulin-like growth factor II (IGF-II) is a polypeptide growth factor thought to be involved in fetal tissue development.  We previously showed an increased expression of IGF-II mRNA in human primary liver cancer.  The present investigation was undertaken to characterize the overexpressed IGF-II transcripts and to determine whether they are translated into protein.  Two cDNAs with distinct 5' untranslated regions, corresponding to IGF-II transcripts expressed in fetal liver, were isolated from a primary liver cancer.  Complete nucleotide sequence analysis showed an identical open reading frame of 540 bp, encoding a predicted polypeptide identical to the IGF-II isolated from serum.  An increased synthesis of IGF-II protein was demonstrated by a protein-binding assay in tumorous liver samples, the highest levels being found in primary liver cancers with the highest IGF-II steady state level.  By contrast, serum IGF-II content was low in most of primary liver cancer cases analyzed.  Altogether, the results indicate reexpression of IGF-II both at the mRNA and protein levels in primary liver cancer.  This finding is consistent with IGF-II being a marker of liver cell differentiation.  In addition, this growth factor might be involved in liver cancer progression by an autocrine and/or paracrine mechanism.