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 immu noreactive protein and enzymatic activity in serum increased in a manner in dependent of de novo protein synthesis, and without any biochemical or immu nohistochemical changes in hepatic DPPIV, during liver regeneration after p artial hepatectomy in rats. DPPIV purified from serum by HAM.4 antibody-bas ed affinity chromatography lacked the NH2-terminal 36 amino acids of the me mbrane-bound enzyme, suggesting that proteolytic cleavage may mediate the r elease of DPPIV into serum. No significant differences in the restoration o f liver mass or in hepatic DNA synthesis were apparent between DPPIV-defici ent and normal rats after partial hepatectomy, suggesting that DPPIV may no t be essential for hepatic regeneration.