TISSUE DISTRIBUTION OF LIVER REGULATING PROTEIN - EVIDENCE FOR A CELLRECOGNITION SIGNAL COMMON TO LIVER, PANCREAS, GONADS, AND HEMATOPOIETIC TISSUES

Liver regulating protein (LRP) is an integral plasma membrane protein that plays a critical role in maintaining the differentiated phenotype of adult rat hepatocytes by mediating cell-cell interactions with rat liver epithelial cells. Using a specific monoclonal antibody (MAb L8) capable of inhibiting the interactions between these two cell types, the cellular distribution of LRP was analyzed in the liver. Various ce ll types, including hepatocytes and several sinusoidal cells, were fou nd to be positive, whereas vascular endothelial cells and bile duct ce lls were consistently negative. This observation led us to question wh ether cells of nonhepatic origin would also express LRP. We show that MAb L8 immunoreactive material was detected in only three groups of ti ssues and corresponded to molecules weights. LRP-like molecules were d emonstrated on acinar cells of the exocrine pancreas and on all hemopo ietic cells regardless of their localization in the organism. LRP-like molecules were also expressed by germ cells and surrounding feeder ce lls in the testis and ovary in a stage-dependent manner. These results demonstrate the existence of a family of LRP proteins and strongly su ggest a critical role for these molecules in regulating cell-cell comm unication in specific tissues.