Distinct mechanisms regulate TIMP-1 expression at different stages of phorbol ester-mediated differentiation of U937 cells.
Upon exposure to 12-O-tetradecanoylphorbol 13-acetate (PMA), promonocyte-like U937 cells differentiate into macrophage-like cells and begin to express certain metalloproteinases and TIMP-1. We report here that distinct mechanisms regulate TIMP-1 production in PMA-treated U937 cells. TIMP-1 protein and steady-state mRNA levels increased about 10-fold in PMA-differentiated cells compared to undifferentiated cells. TIMP-1 transcription increased about 2.5-fold, but this stimulation was not detected until at least 48 h post-PMA. In contrast, the half-life for TIMP-1 mRNA increased about 3-fold and was detected at 8 h post-PMA. Using in vitro translation assays, we found that TIMP-1 mRNA from PMA-differentiated cells translated about 5-fold less efficiently than that from basal cells, suggesting structural differences in TIMP-1 mRNA in basal and differentiated U937 cells. Although primer extension and RNase protection analyses showed 5' heterogeneity of TIMP-1 transcripts, all forms were equally stimulated in response to PMA-mediated differentiation. The poly(A) tail length of TIMP-1 mRNA, however, was longer in PMA-treated cells. Our findings suggested that up-regulation of TIMP-1 expression in PMA treated U937 cells is mediated early by enhanced TIMP-1 mRNA stability, possibly related to increased poly(A) tail length, and later by an increase in transcription rate.
Doyle
G A
GA
Department of Medicine (Dermatology), Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Saarialho-Kere
U K
UK
Parks
W C
WC
D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D003907:Dexamethasone / Q000494:pharmacology; D006023:Glycoproteins / Q000096:biosynthesis* / Q000235:genetics; D006801:Humans; D061965:Matrix Metalloproteinase Inhibitors; D008666:Metalloendopeptidases / Q000037:antagonists & inhibitors*; D009000:Monocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D011061:Poly A / Q000378:metabolism; D011480:Protease Inhibitors / Q000378:metabolism*; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D019714:Tissue Inhibitor of Metalloproteinases; D014158:Transcription, Genetic / Q000187:drug effects
D006023:Glycoproteins; D061965:Matrix Metalloproteinase Inhibitors; D011480:Protease Inhibitors; D012333:RNA, Messenger; D019714:Tissue Inhibitor of Metalloproteinases; D011061:Poly A; D003907:Dexamethasone; D008666:Metalloendopeptidases; D013755:Tetradecanoylphorbol Acetate