TRANSCRIPTIONAL AND POSTTRANSCRIPTIONAL CONTROL OF LYSYL OXIDASE EXPRESSION IN VASCULAR SMOOTH-MUSCLE CELLS - EFFECTS OF TGF-BETA-1 AND SERUM DEPRIVATION

Transforming growth factor-beta 1 (TGF-beta 1) markedly reduced cell p roliferation and elevated steady state lysyl oxidase (LO) mRNA 3-fold in neonatal rat aorta smooth muscle cells cultured in medium containin g 10% fetal bovine serum. The increase in LO mRNA was prevented by the presence of cycloheximide, indicative of controlling events at the le vel of protein synthesis. The basal level of mRNA in cells proliferati ng in 10% fetal bovine serum in the absence of TGF-beta 1 was enhanced 7-fold upon decreasing growth by shifting to medium containing 0.5% s erum. Changes in LO activity paralleled those in LO mRNA. Nuclear run- on assays revealed that the stimulation of expression in 0.5% serum in volved increased gene transcription whereas that caused by TGF-beta 1 was mostly post-transcriptional in origin. LO mRNA was quite labile (t (1/2) approximately 3 h) in 10% serum but was markedly stabilized (t(1 /2) > 12 h) by the presence of TGF-beta 1 in the 10% serum medium. LO mRNA was also considerably more stable under retarded growth condition s (0.5% serum) in the absence of TGF-beta 1. LO promoter activity in l uciferase reporter constructs transfected into these cells was low and not significantly affected by the addition of TGF-beta 1 to the 10% s erum medium but was markedly elevated by shifting from 10 to 0.5% seru m in the absence of TGF-beta 1. Thus, LO expression is inversely corre lated with cell proliferation, and is subject to control at transcript ional and post-transcriptional levels. TGF-beta 1 enhances LO expressi on in these cells by dramatically stabilizing LO mRNA. (C) 1997 Wiley- Liss, Inc.