Growth-related expression of the ectonucleotide pyrophosphatase PC-1 in rat liver

Plasma cell differentiation antigen-1 (PC-1) is a 5'-ectonucleotide pyrophosphatase that has been implicated in various processes including insulin- and nucleotide-mediated signaling and cell growth. We show here that the expression of both PC-1 mRNA and protein in rat liver and in hepatoma cells is strictly growth-related. Thus, the level of PC-1 in FAO hepatoma cells increased with the cell density. PC-1 was not expressed in the neonatal rat liver, but gradually appeared in the first weeks of age, to reach adult levels around the weaning period. Furthermore, PC-1 protein and mRNA largely disappeared from the liver within 24 hours following a hepatectomy of 70%, but re-appeared in the later phases (3-15 days) of the ensuing regeneration period. An equally rapid loss of PC-1 protein and mRNA could also be provoked in normal livers by the administration of the translational inhibitor, cycloheximide, but the transcriptional inhibitors, actinomycin D and alpha-amanitin, did not show these effects. Nuclear run-on assays revealed that the loss of PC-1 mRNA after hepatectomy or after the administration of cycloheximide was not caused by a decreased transcription of the PC-1 gene, suggesting that the level of PC-1 is controlled by an mRNA-stabilizing protein that is lost after hepatectomy and has a high turnover.