Identification of bile canalicular cell surface antigen HAM.4 as dipeptidyl peptidase IV (DPPIV) and characterization of its role in hepatic regeneration after partial hepatectomy in rats.

Dipeptidyl peptidase IV (DPPIV) has been implicated in the control of cell growth and differentiation. A rat hepatocyte membrane antigen recognized by a monoclonal antibody (HAM.4) has now been shown to be identical to DPPIV by immunoblot analysis and amino acid sequencing. The amounts of DPPIV immunoreactive protein and enzymatic activity in serum increased in a manner independent of de novo protein synthesis, and without any biochemical or immunohistochemical changes in hepatic DPPIV, during liver regeneration after partial hepatectomy in rats. DPPIV purified from serum by HAM.4 antibody-based affinity chromatography lacked the NH2-terminal 36 amino acids of the membrane-bound enzyme, suggesting that proteolytic cleavage may mediate the release of DPPIV into serum. No significant differences in the restoration of liver mass or in hepatic DNA synthesis were apparent between DPPIV-deficient and normal rats after partial hepatectomy, suggesting that DPPIV may not be essential for hepatic regeneration.