EXPRESSION OF ALPHA(2)-MACROGLOBULIN BY THE INTERACTION BETWEEN HEPATOCYTES AND ENDOTHELIAL-CELLS IN COCULTURE

The interaction between distinct cell types within the liver seems to be important in regulating hepatic function. However, these interactio ns have not been well characterized because of difficulty in reproduci ng the hepatic environment in an ex vivo model. In the present study a coculture system of hepatocytes and endothelial cells was established to investigate the communication between parenchymal and nonparenchym al cells. Freshly isolated rat hepatocytes were placed onto a monolaye r of primary aortic rat endothelial cells. Analysis of the proteins se creted into the extracellular medium after pulse labeling with radioac tive amino acids revealed the presence of a 180,000-apparent molecular weight glycoprotein, BBB-180, which was not detected in the extracell ular medium of hepatocytes or endothelial cells when they were culture d separately. This glycoprotein was identified as alpha(2)-macroglobul in after sequencing of the proteolytic peptides derived from the purif ied protein. This finding was confirmed by Northern and Western blotti ng, immunoprecipitation, and RT-PCR. The expression of alpha(2)-macrog lobulin required direct contact between hepatocytes and viable endothe lial cells. These findings suggest that endothelial cells modulate hep atocyte gene expression by direct cellular interactions.