CELL CAM-105 ISOFORM RNA EXPRESSION IS DIFFERENTIALLY REGULATED DURING RAT-LIVER REGENERATION AND CARCINOGENESIS

Cell CAM 105 (C-CAM) is a member of the carcinoembryonic antigen famil y and has been characterized as a rat hepatocyte cell-cell adhesion mo lecule via antibody activity. Two isoforms have been cloned and differ primarily in the length of the cytoplasmic domain. Despite extensive structural studies, little is known about their function and regulatio n in vivo. We have examined C-CAM expression during rat liver regenera tion and hepatocarcinogenesis. Steady-state C-CAM RNA varied less than 3-fold during regeneration with subtle changes in the isoform ratio b oth before and after hepatocyte division. In liver tumors and transfor med cells derived from tumors, however, large-scale decreases were obs erved in C-CAM RNA with wide variations in isoform ratios. In general, RNA decreases were reflected at the protein level. Our data suggest w hereas down-regulation and alterations in C-CAM isoform ratio are tran sient during regulated liver growth, they are permanent in malignancy and may modulate hepatocyte adhesion.