Cloning and characterization of newly described proteins from a fat-storing cell library : their significance in the activation of the cells.

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Fat-storing cells (FSC) transform into myofibroblasts and play an important role in liver fibrogenesis. We isolated two cDNAs, C72 and C81, from a rat fat-storing cell library.C72 cDNA contained an open reading frame coding for a protein of 468 amino acid residues. C72 cDNA had a nucleotide sequence homologous to that of the gene for the type I procollagen C-proteinase enhancer protein (PCPE). C72 cDNA recognized by Northern blot a 1.7 kb mRNA in total RNA extracted from freshly isolated and early passaged FSC and fibroblasts. The expression of C72 mRNA was increased 3-fold in early passaged FSC as compared to freshly isolated FSC.C72 mRNA was not detected in total rat liver, freshly isolated hepatocytes, endothelial or Kupffer cells. However, the expression of C72 mRNA was induced in CC1_4-cirrhotic livers. On the other hand, we revealed that the derived C-terminus of the cDNA contains motifs specific to RNA-binding consensus sequence, suggesting that PCPE has a function other than the enhancer activity. The down-regulation of PCPE with an antisense oligonucleotide inhibited non-collagenous protein production as well as collagen production in FSC.C81 cDNA contained an open reading frame which codes 563 amino acid residues. Its deduced amino acid sequence showed no significant homology to previously reported proteins. C81 cDNA hybridized with a 2.1 kb mRNA presented in freshly isolated FSC.The hybridization band disappeared in early passaged FSC,and no signals were detected in fibroblasts.From these results, these cDNAs can be useful tools to follow the transformation of HSC to myofibroblasts during development of hepatic fibrosis.