Molecular cloning and functional expression analysis of a cDNA for human hepassocin, a liver-specific protein with hepatocyte mitogenic activity

• Published in: Biochimica et biophysica acta Vol. 1520; no. 1; pp. 45 - 53
• Main Authors: Hara, Hiroshi, Yoshimura, Hiromitsu, Uchida, Saeko, Toyoda, Yumiko, Aoki, Mari, Sakai, Yoshiko, Morimoto, Shigeo, Shiokawa, Koichiro
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 30.07.2001
• Subjects: Amino Acid Sequence; Animals; Base Sequence; Blotting, Western; cDNA cloning; Cells, Cultured; CHO Cells; Cloning, Molecular; Cricetinae; Dihydrofolate reductase–methotrexate gene amplification; DNA, Complementary - biosynthesis; DNA, Complementary - chemistry; Dogs; Hepassocin; Humans; Liver - metabolism; Liver regeneration; Mice; Mitogenic activity; Mitogens - genetics; Molecular Sequence Data; Neoplasm Proteins; Open Reading Frames; Protein Structure, Secondary; Proteins - chemistry; Proteins - genetics; Proteins - metabolism; Rabbits; Rats; RNA, Messenger - analysis; RNA, Messenger - biosynthesis; Transfection; cDNA cloning; Hepassocin; Dihydrofolate reductase–methotrexate gene amplification; Mitogenic activity; Liver regeneration
• ISSN: 0167-4781; 0006-3002; 1879-2634
• DOI: 10.1016/S0167-4781(01)00249-4

By means of differential cDNA expression cloning, we earlier isolated a novel rat cDNA and its protein, named hepassocin, which is upregulated during liver regeneration. Using the rat cDNA as a probe, we have now isolated human hepassocin cDNA encoding a protein of 312 amino acids, which has 81.4% and 83.8% identity, respectively, to rat hepassocin before and after elimination of its signal peptide. Dot blot analysis revealed that hepassocin mRNA was strongly expressed in adult liver, fairly strongly in fetal liver, and weakly in pancreas, but not in other tissues. Recombinant human hepassocin produced in Chinese hamster ovary (CHO) cells by the dihydrofolate reductase–methotrexate (DHFR–MTX) gene amplification method is a homodimer (68 kDa) and has mitogenic activities in hepatocytes of various animal species including rat, mouse, rabbit and dog, and the activity was lost with 2-mercaptoethanol treatment. These results suggest that hepassocin is a potent regulator in liver cell growth not only in rats but also in humans. Computer searches revealed that human hepassocin as well as rat hepassocin has a characteristic disulfide structure close to that of fibrinogen-γ. We assume that this newly identified growth factor exerts functions in association with an extracellular matrix such as fibrinogen.