A novel gene (HIP) activated in human primary liver cancer

Differential screening of a human hepatocellular carcinoma complementary DNA library using subtracted probes allowed us to identify a novel gene named HIP whose expression at the transcriptional level was elevated in liver tumors. The protein potentially encoded by the complementary DNA showed 68.5% identity with the bovine pancreatic thread protein and 49% identity with the human reg protein, which has been proposed as a pancreatic islet cell regenerating factor and is identical to the pancreatic stone or pancreatic thread protein. Sequence analysis suggests that the bovine pancreatic thread protein encoding gene is, in fact, the bovine homologue of the HIP gene. Furthermore, data base searches revealed a significant similarity of the HIP and pancreatic stone protein/pancreatic thread protein/reg sequences with the C-type lectin superfamily. The HIP sequence, like pancreatic stone protein/pancreatic thread protein/reg protein, consists of a single carbohydrate recognition domain linked to a signal peptide which would be involved in secretion of the protein. HIP mRNA was expressed at a high level in the tumors of seven of 29 hepatocellular carcinomas. In contrast, HIP mRNA was not detected in nontumorous adjacent areas or in normal adult and fetal liver, suggesting that HIP could be involved in liver cell proliferation or differentiation. HIP mRNA expression is tissue specific, since it is present in the normal small intestine and pancreas, while it could not be evidenced in colon, brain, kidney, or lung. In summary, our results show the existence of a novel family within the superfamily of C-type lectin which may be involved in liver, pancreatic, and intestinal cell proliferation or differentiation.