Plasma cell differentiation antigen-1 (PC-I) is a 5'-ectonucleotide pyropho
sphatase that has been implicated in various processes including insulin- a
nd nucleotide-mediated signaling and cell growth, We show here that the exp
ression 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 inc
reased with the cell density. PC-1 was not expressed in the neonatal rat li
ver, but gradually appeared in the first weeks of age, to reach adult level
s around the weaning period, Furthermore, PC-1 protein and mRNA largely dis
appeared 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 pe
riod. An equally rapid loss of PC-l protein and mRNA could also be provoked
in normal livers by the administration of the translational inhibitor, cyc
loheximide, but the transcriptional inhibitors, actinomycin D and ol-amanit
in, did not show these effects. Nuclear run-on assays revealed that the los
s of PC-1 mRNA after hepatectomy or after the administration of cycloheximi
de 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 i
s lost after hepatectomy and has a high turnover.