Abstract
Cell death and cell survival are central components of normal development and pathologic states. Transforming growth factor beta1 (TGF-beta1) is a pleiotropic cytokine that regulates both cell growth and cell death. To better understand the molecular mechanisms that control cell death or survival, we investigated the role of TGF-beta1 in the apoptotic process by dominant-negative inhibition of both TGF-beta1 and mitogen-activated protein kinase (MAPK) signaling pathways. Murine macrophages (RAW 264.7) undergo apoptosis following serum deprivation, as determined by DNA laddering assay. However, apoptosis is prevented in serum-deprived macrophages by the presence of exogenous TGF-beta1. Using stably transfected RAW 264.7 cells with the kinase-deleted dominant-negative mutant of TbetaR-II (TbetaR-IIM) cDNA, we demonstrate that this protective effect by TGF-beta1 is completely abrogated. To determine the downstream signaling pathways, we examined TGF-beta1 effects on the MAPK pathway. We show that TGF-beta1 induces the extracellular signal-regulated kinase (ERK) activity in a time-dependent manner up to 4 h after stimulation. Furthermore, TGF-beta1 does not rescue serum deprivation-induced apoptosis in RAW 264.7 cells transfected with a dominant-negative mutant MAPK (ERK2) cDNA or in wild type RAW 264.7 cells in the presence of the MAPK kinase (MEK1) inhibitor. Taken together, our data demonstrate for the first time that TGF-beta1 is an inhibitor of apoptosis in cultured macrophages and may serve as a cell survival factor via TbetaR-II-mediated signaling and downstream intracellular MAPK signaling pathway.
Highlights
From the ‡Toxicological Sciences, Environmental Health Sciences, and ¶Division of Pulmonary and Critical Care Medicine, The Johns Hopkins Medical Institutions, Baltimore, Maryland 21205 and the ʈSection of Pulmonary and Critical Care Medicine and ‡‡Section of Nephrology, Department of Internal Medicine, Yale University School of Medicine and the Veterans Affairs Connecticut Healthcare Systems, New Haven, Connecticut 06520
Transforming growth factor 1 (TGF-1) Rescues Serum-deprived RAW 264.7 Cells from Apoptosis—Given that previous studies have implicated the role of TGF-1 as a modulator of apoptosis, we examined the effects of TGF-1 on serum deprivation-induced apoptosis in RAW 264.7 cells
Treatment with exogenous TGF-1 (10 ng/ml) resulted in increased cell survival of 93 Ϯ 2% compared with 78 Ϯ 3% after serum deprivation for 24 h (p Ͻ 0.01, Student’s t test, n ϭ 3) and 88 Ϯ 4% compared with 49 Ϯ 2% cell survival after serum deprivation for 48 h (p Ͻ 0.005, Student’s t test, n ϭ 3)
Summary
(Received for publication, October 5, 1998, and in revised form, January 8, 1999). Beek Yoke Chin‡§, Irina Petrache¶, Augustine M. To better understand the molecular mechanisms that control cell death or survival, we investigated the role of TGF-1 in the apoptotic process by dominant-negative inhibition of both TGF-1 and mitogen-activated protein kinase (MAPK) signaling pathways. TGF-1 Inhibits Apoptosis via ERK Pathway support the involvement of the mitogen-activated protein kinase (MAPK) pathways in TGF-1 signaling [11,12,13,14]. To better understand the molecular mechanism controlling cell death or survival, we investigated the role of TGF-1 in the apoptotic process by dominant-negative inhibition of both TGF-1 and MAPK signaling pathways. TGF-1 fails to rescue RAW 264.7 cells from serum deprivation-induced apoptosis upon stable transfection with a dominant-negative mutant MAPK (ERK2) cDNA or in the presence of the MEK1 inhibitor. Our data suggest that TGF-1 rescues macrophages from serum deprivation-induced apoptosis via TR-IImediated signaling and downstream intracellular MAPK signaling pathway
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