Growth–Related Expression of the Ectonucleotide Pyrophosphatase Pc–1 in Rat Liver

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Abstract
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 α–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.

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