Transforming Growth Factor β1 Rescues Serum Deprivation-induced Apoptosis via the Mitogen-activated Protein Kinase (MAPK) Pathway in Macrophages

Cell death and cell survival are central components of normal development and pathologic states. Transforming growth factor β1 (TGF-β1) 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-β1 in the apoptotic process by dominant-negative inhibition of both TGF-β1 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-β1. Using stably transfected RAW 264.7 cells with the kinase-deleted dominant-negative mutant of TβR-II (TβR-IIM) cDNA, we demonstrate that this protective effect by TGF-β1 is completely abrogated. To determine the downstream signaling pathways, we examined TGF-β1 effects on the MAPK pathway. We show that TGF-β1 induces the extracellular signal-regulated kinase (ERK) activity in a time-dependent manner up to 4 h after stimulation. Furthermore, TGF-β1 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-β1 is an inhibitor of apoptosis in cultured macrophages and may serve as a cell survival factor via TβR-II-mediated signaling and downstream intracellular MAPK signaling pathway. Cell death and cell survival are central components of normal development and pathologic states. Transforming growth factor β1 (TGF-β1) 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-β1 in the apoptotic process by dominant-negative inhibition of both TGF-β1 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-β1. Using stably transfected RAW 264.7 cells with the kinase-deleted dominant-negative mutant of TβR-II (TβR-IIM) cDNA, we demonstrate that this protective effect by TGF-β1 is completely abrogated. To determine the downstream signaling pathways, we examined TGF-β1 effects on the MAPK pathway. We show that TGF-β1 induces the extracellular signal-regulated kinase (ERK) activity in a time-dependent manner up to 4 h after stimulation. Furthermore, TGF-β1 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-β1 is an inhibitor of apoptosis in cultured macrophages and may serve as a cell survival factor via TβR-II-mediated signaling and downstream intracellular MAPK signaling pathway. Apoptosis, the process of programmed cell death, is an integral part of normal embryonic development, inflammatory response, and tumorigenesis (1Ashkenazi A. Dixit V.M. Science. 1998; 281: 1305-1308Crossref PubMed Scopus (5154) Google Scholar). It is a highly regulated series of well coordinated events characterized by distinctive morphologic and biochemical changes involving nuclear and chromatin condensation, cell membrane blebbing, and loss of cellular integrity forming distinct apoptotic bodies, as well as endonuclease activity resulting in DNA fragmentation and ultimately cell death (2Steller H. Science. 1995; 267: 1445-1449Crossref PubMed Scopus (2431) Google Scholar). Regulatory mechanisms controlling cell death is as fundamental as those regulating cell growth in achieving the homeostatic balance between cell survival and cell death and involve a complex interplay of specific regulatory genes in signaling cells to either live or die. Transforming growth factor β1(TGF-β1) 1The abbreviations used are: TGF-β1, transforming growth factor β1; TβR, TGF-β receptor; MAPK, mitogen-activated protein kinase; ERK, extracellular signal-regulated kinase; PCR, polymerase chain reaction; DMEM, Dulbecco's modified Eagle's medium; FBS, fetal bovine serum; JNK/SAPK, c-Jun N-terminal kinase/stress-activated protein kinase. is a 25-kDa polypeptide, belonging to a superfamily of multifunctional cytokines, that regulates cellular growth and differentiation and extracellular matrix production (3Attisano L. Wrana J.L. Cytokine Growth Factor Rev. 1996; 7: 327-339Crossref PubMed Scopus (144) Google Scholar). Moreover, TGF-β1 has been shown to be a potent modulator of apoptosis in a variety of cell types, including epithelial cells, hepatocytes, hematopoietic cells, and lymphocytes, which undergo programmed cell death in response to TGF-β1 (4Rotello R.J. Lieberman R.C. Purchio A.F. Gerschenson L.E. Proc. Natl. Acad. Sci. U. S. A. 1991; 88: 3412-3415Crossref PubMed Scopus (282) Google Scholar, 5Oberhammer F.A. Pavelka M. Sharma S. Riefenbacher R. Purchio A.F. Bursch W. Schulte-Hermann R. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 5408-5412Crossref PubMed Scopus (680) Google Scholar, 6Lotem J. Sachs L. Blood. 1992; 80: 1750-1757Crossref PubMed Google Scholar, 7Andjelic S. Khanna A. Suthanthiran M. Nikolic-Zugic J. J. Immunol. 1997; 158: 2527-2534PubMed Google Scholar). We have previously reported the induction of apoptosis by TGF-β1 in endothelial cells (8Choi M.E. Ballermann B.J. J. Biol. Chem. 1995; 270: 21144-21150Crossref PubMed Scopus (132) Google Scholar). However, more recent studies suggest that TGF-β1 also possesses the ability to inhibit apoptosis, further affirming the multifunctional nature of this cytokine (9Sachsenmeier K.F. Sheibani N. Schlosser S.J. Allen-Hoffmann B.L. J. Biol. Chem. 1996; 271: 5-8Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar). TGF-β1 elicits multiple biological responses by interaction with two transmembrane receptor serine/threonine kinases known as TGF-β type I receptor (TβR-I) and TGF-β type II receptor (TβR-II) (3Attisano L. Wrana J.L. Cytokine Growth Factor Rev. 1996; 7: 327-339Crossref PubMed Scopus (144) Google Scholar). TβR-II is a constitutively active kinase, which binds TGF-β1 directly and recruits TβR-I to form a “heteromeric” complex, and the signaling cascade is initiated upon transphosphorylation of the GS domain of TβR-I by TβR-II (10Wrana J.L. Attisano L. Wieser R. Ventura F. Massagué J. Nature. 1994; 370: 341-347Crossref PubMed Scopus (2114) Google Scholar). TβR-I alone does not exhibit significant binding of TGF-β1 ligand when assessed by cross-linking analysis, and TβR-II is unable to signal without TβR-I (10Wrana J.L. Attisano L. Wieser R. Ventura F. Massagué J. Nature. 1994; 370: 341-347Crossref PubMed Scopus (2114) Google Scholar). Thus, TβR-II is required for initial ligand binding and phosphorylation of TβR-I to initiate the signaling cascade. We have previously reported the critical role of TβR-II in the TGF-β1 signaling pathway to induce apoptosis in endothelial cells (8Choi M.E. Ballermann B.J. J. Biol. Chem. 1995; 270: 21144-21150Crossref PubMed Scopus (132) Google Scholar). Interference with TβR-II-mediated signal transduction by a dominant-negative mutant of TβR-II blocked TGF-β1-induced endothelial cell apoptosis and associated capillary morphogenesis in vitro(8Choi M.E. Ballermann B.J. J. Biol. Chem. 1995; 270: 21144-21150Crossref PubMed Scopus (132) Google Scholar). Although molecular cloning of the TGF-β receptors have furthered our understanding of the mechanism of TGF-β1 signaling, the downstream signaling pathways activated after the initial receptor interaction with ligand to mediate multiple TGF-β1responses remain poorly understood. Recent studies support the involvement of the mitogen-activated protein kinase (MAPK) pathways in TGF-β1 signaling (11Yamaguchi K. Shirakabe K. Shibya H. Irie K. Oishi I. Ueno N. Taniguchi T. Nishida E. Matsumoto K. Science. 1995; 270: 2008-2011Crossref PubMed Scopus (1175) Google Scholar, 12Hartsough M.T. Frey R.S. Zipfel P.A. Buard A. Cook S.J. McCormick F. Mulder K.M. J. Biol. Chem. 1996; 271: 22368-22375Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar, 13Atfi A. Djelloul S. Chastre E. Davis R. Gespach C. J. Biol. Chem. 1997; 272: 1429-1432Abstract Full Text Full Text PDF PubMed Scopus (273) Google Scholar, 14Frey R.S. Mulder K.M. Cancer Res. 1997; 57: 628-633PubMed Google Scholar). Moreover, activation of the MAPK-dependent pathways has been implicated in the process of apoptosis (15Adams J.M. Cory S. Science. 1998; 281: 1322-1326Crossref PubMed Scopus (4811) Google Scholar, 16Ip Y.T. Davis R.J. Curr. Opin. Cell Biol. 1998; 10: 205-219Crossref PubMed Scopus (1382) Google Scholar). Members of the MAPK family, like the TGF-β receptors, are structurally related serine/threonine kinases that are actively involved in cellular events such as growth, differentiation, and cellular responses to environmental stress (17Davis R.J. J. Biol. Chem. 1993; 268: 14553-14556Abstract Full Text PDF PubMed Google Scholar, 18Davis R.J. Trends Biochem. Sci. 1994; 19: 470-473Abstract Full Text PDF PubMed Scopus (917) Google Scholar). There are three groups of the MAPK family members identified to date: the extracellular signal-regulated kinases 1 and 2 (ERK1 and ERK2), also known as p44 and p42 MAPKs, respectively; the c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK); and the p38 (18Davis R.J. Trends Biochem. Sci. 1994; 19: 470-473Abstract Full Text PDF PubMed Scopus (917) Google Scholar,19Nishida E. Gotoh Y. Trends Biochem. Sci. 1993; 18: 128-131Abstract Full Text PDF PubMed Scopus (961) Google Scholar). The signal transduction cascades involved in the activation of MAPKs require a well coordinated series of three protein kinase reactions, propagating the phosphorylation and the activation of the next kinase in their respective pathways. The MAPKs require dual phosphorylation at the threonine and tyrosine sites by MAPK kinases, the MEKs and MKKs that are specific for ERK, JNK, and p38, which are in turn activated by MAPK kinase kinases (MKKKs) via serine/threonine phosphorylation (19Nishida E. Gotoh Y. Trends Biochem. Sci. 1993; 18: 128-131Abstract Full Text PDF PubMed Scopus (961) Google Scholar, 20Whitmarsh A.J. Cavanagh J. Tournier C. Yasuda J. Davis R.J. Science. 1998; 281: 1671-1674Crossref PubMed Scopus (589) Google Scholar). The MAPK cascades display evolutionary conservation and are implicated to play essential roles in the regulation of cell growth, differentiation, and apoptosis. To better understand the molecular mechanism controlling cell death or survival, we investigated the role of TGF-β1 in the apoptotic process by dominant-negative inhibition of both TGF-β1 and MAPK signaling pathways. In this study, we utilized serum withdrawal or deprivation to induce apoptosis by decreased availability of cell survival factors. We show that serum deprivation induces apoptosis in murine macrophages (RAW 264.7) and that TGF-β1 is able to prevent serum-deprived macrophages from undergoing apoptosis. This “rescue” is inhibited in cells transfected with a dominant-negative mutant of TβR-II (TβR-IIM), suggesting the critical role of TβR-II in TGF-β1 signaling to prevent serum deprivation-induced apoptosis. Furthermore, we demonstrate that TGF-β1 rapidly induces ERK1/ERK2 MAPK activity. TGF-β1 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. Taken together, our data suggest that TGF-β1 rescues macrophages from serum deprivation-induced apoptosis via TβR-II-mediated signaling and downstream intracellular MAPK signaling pathway. Recombinant human TGF-β1 and TGF-α were obtained from Life Technologies, Inc. The MAPK, MAPK and and and p38 were from Inc. The MEK1 also obtained from Inc. TβR-II (TβR-IIM), the serine/threonine kinase the transmembrane and extracellular by polymerase chain a TβR-II cDNA as the as previously (8Choi M.E. Ballermann B.J. J. Biol. Chem. 1995; 270: 21144-21150Crossref PubMed Scopus (132) Google Scholar). were as the for the for and a in the The the a a and of the in were by with and and by the chain The type and the mutant of used in this were by M. E. C. R. Science. 1995; PubMed Scopus Google Scholar). The murine cell RAW obtained from The cells were in Dulbecco's modified Eagle's Technologies, with and in a of and at To that stably RAW 264.7 cells were transfected Technologies, as to on were with of DNA (TβR-IIM) and of in at in a in to a of and further for the to in and for To for cells were up to Technologies, in FBS, and the at after transfection and were and in FBS, and stably transfected the and were of obtained by chain that that the transfected and not the To that stably the or the the were with a a as The stable were also in and and in of obtained by To induce apoptosis, cells on to were in for In involving with cytokines, the cells were in the or presence of exogenous TGF-β1 or TGF-α at for In with MEK1 cells were in the or presence of for The of as is the without cellular in involving of RAW 264.7 cells to the cells were in a with and at cells were in and at DNA the to the cells were directly on the after with by a with A. The cell were for and at for to the to the an the DNA and and on The stable were in the presence or of 1 for h to serum deprivation and with exogenous TGF-β1. The and stable were also to serum withdrawal and TGF-β1 as of the at three of cell by assay. on to were to undergo apoptosis as and at the time cells in of the were and in of of were with Technologies, for by cell by live and cells were from the The were as of cells that not up the in the cell The were in and two cellular were obtained for the by of cells in 1 1 and of the cell were determined by of and and the were for were on The were with MAPK, MAPK, or p38 for by with for development and to were as by R. J. R. 1993; Full Text PDF PubMed Scopus Google with cells were in 1 1 1 1 1 and 1 and were determined as for protein were with MAPK on a at 4 a of active MAPK (ERK2) with control cell were to the activated MAPK The were with 1 of protein in the presence of and a kinase 2 and The with and The were on and as for activity by of a with the at 4 the membrane for 1 h with a at with The were and to of the were three of the data for the cell survival by determined by of or the for as were are as of We first determined RAW 264.7 cells apoptosis following withdrawal of DNA from RAW 264.7 cells were assessed for the presence of DNA fragmentation by a on of a of apoptosis. The induction of DNA fragmentation in RAW 264.7 cells after h of serum deprivation that studies have implicated the role of TGF-β1 as a modulator of apoptosis, we examined the effects of TGF-β1 on serum deprivation-induced apoptosis in RAW 264.7 shown in DNA fragmentation not in RAW 264.7 cells upon serum deprivation in the presence of exogenous TGF-β1 and This inhibition of DNA fragmentation by TGF-β1 associated with cell survival, as shown in with exogenous TGF-β1 in cell survival of with after serum deprivation for h and with cell survival after serum deprivation for h The cell survival with TGF-β1 significant up to h following serum an of growth distinct from TGF-β1 and a tyrosine kinase receptor to prevent DNA fragmentation in serum-deprived RAW 264.7 cells not Furthermore, TGF-β1 not rescue the apoptotic process by such as stress 2 of rescue from serum deprivation-induced apoptosis in RAW 264.7 of TGF-β1 effect on cell survival in serum-deprived RAW 264.7 in the presence of or in with and without exogenous TGF-β1 for the time as were assessed for cell by as The were as of cells that not up the in the cell data is the of a significant in survival of cells with TGF-β1 with the respective control in without TGF-β1 for time cell survival decreased upon serum deprivation in the of exogenous TGF-β1 of To determine the ability of TGF-β1 to rescue RAW 264.7 cells from serum deprivation-induced apoptosis by we first stably transfected cells a dominant-negative mutant of TβR-II that TGF-β1 signal transduction of TβR-II and TβR-I and transphosphorylation of TβR-I by the receptor which is the serine/threonine kinase for binding to in a dominant-negative to inhibit TGF-β1 signaling (8Choi M.E. Ballermann B.J. J. Biol. Chem. 1995; 270: 21144-21150Crossref PubMed Scopus (132) Google R. Attisano L. Wrana J.L. Massagué J. Biol. 1993; PubMed Google Scholar). inhibition of TGF-β1 rescue from serum deprivation-induced apoptosis in cells from two and the receptors, This both with and without Although the a of activity and has been previously by and (8Choi M.E. Ballermann B.J. J. Biol. Chem. 1995; 270: 21144-21150Crossref PubMed Scopus (132) Google Scholar, S. Proc. Natl. Acad. Sci. U. S. A. 1993; PubMed Scopus Google Scholar). studies have that biological effects via the MAPK signaling pathway in cell (11Yamaguchi K. Shirakabe K. Shibya H. Irie K. Oishi I. Ueno N. Taniguchi T. Nishida E. Matsumoto K. Science. 1995; 270: 2008-2011Crossref PubMed Scopus (1175) Google Scholar, 12Hartsough M.T. Frey R.S. Zipfel P.A. Buard A. Cook S.J. McCormick F. Mulder K.M. J. Biol. Chem. 1996; 271: 22368-22375Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar, 13Atfi A. Djelloul S. Chastre E. Davis R. Gespach C. J. Biol. Chem. 1997; 272: 1429-1432Abstract Full Text Full Text PDF PubMed Scopus (273) Google Scholar, 14Frey R.S. Mulder K.M. Cancer Res. 1997; 57: 628-633PubMed Google Scholar). We first determined the of and protein in RAW 264.7 cells with exogenous TGF-β1 by MAPK and MAPK The MAPK the of the MAPK ERK1/ERK2 shown in in phosphorylation of and were in cells, as as after with exogenous TGF-β1. There were in the activation of or p38 the time of TGF-β1 We next examined this induction of and by TGF-β1 associated with an in MAPK activity an kinase assay. from RAW 264.7 cells in the presence or or exogenous were to MAPK The resulting active ERK1/ERK2 to and activity by the of by TGF-β1 the of the form of Although activity in the control cells, TGF-β1 activity of TGF-β1 with activity up to 4 h of TGF-β1 that TGF-β1 the MAPK (ERK) pathway in RAW 264.7 cells, we next examined the MAPK signaling pathway the TGF-β1 rescue of RAW 264.7 cells from serum deprivation-induced apoptosis. first to inhibit the MAPK pathway by a dominant-negative mutant of MAPK that TGF-β1 rescues serum deprivation-induced apoptosis in cells transfected with as previously in RAW 264.7 However, in RAW 264.7 cells that have been transfected with a dominant-negative mutant DNA fragmentation both in the presence of serum and upon serum deprivation, and with exogenous TGF-β1 to prevent apoptosis This that the rescue effect of TGF-β1 is in part by the MAPK signaling pathway. To further the role of the MAPK pathway in TGF-β1 rescue of serum deprivation-induced apoptosis, we next utilized a inhibitor of MEK1 of In RAW 264.7 cells with of the MEK1 inhibitor for DNA fragmentation both in the presence of serum and and upon serum deprivation and and with exogenous TGF-β1 to prevent apoptosis. Taken together, suggest that MEK1 the signaling process of exogenous TGF-β1 by the activation of the MAPK pathway of serum deprivation, the of apoptotic It is well that the process of programmed cell death, or apoptosis, as a critical in the development and of and is regulated by that the of a cell between and death. may to either or inhibit apoptosis, and the signal may have effects on cell such signaling that may both and is the multifunctional cytokine TGF-β1, both a potent and an inhibitor of cell In the study, we examined the role of TGF-β1 in apoptosis in cultured macrophages (RAW 264.7 In to induce apoptosis, serum deprivation has been shown to apoptosis in a variety of cells including and endothelial cells, as a of decreased availability of cell survival (8Choi M.E. Ballermann B.J. J. Biol. Chem. 1995; 270: 21144-21150Crossref PubMed Scopus (132) Google Scholar, A. E. J. Biochem. 1997; PubMed Scopus Google Scholar). We that macrophages also undergo apoptosis upon serum withdrawal or deprivation, as determined by of the DNA laddering the presence of exogenous TGF-β1 prevented the macrophages from undergoing apoptosis upon serum withdrawal 2 This inhibition of DNA laddering by TGF-β1 also associated with cell survival The activity of TGF-β1 further by to rescue cells from serum deprivation-induced apoptosis when signaling receptors are blocked by a kinase-deleted dominant-negative mutant of TβR-II signal transduction of TβR-II and the mutant receptor for binding to in a dominant-negative (3Attisano L. Wrana J.L. Cytokine Growth Factor Rev. 1996; 7: 327-339Crossref PubMed Scopus (144) Google Scholar, M.E. Ballermann B.J. J. Biol. Chem. 1995; 270: 21144-21150Crossref PubMed Scopus (132) Google Scholar, J.L. Attisano L. Wieser R. Ventura F. Massagué J. Nature. 1994; 370: 341-347Crossref PubMed Scopus (2114) Google Scholar). In stably transfected RAW 264.7 cells the apoptosis with serum deprivation, both in the presence or of exogenous TGF-β1 that the effect by TGF-β1 is by TβR-II kinase. Although TGF-β1 has been shown in a of to be a potent of apoptosis, of TGF-β1 are well reported effects of TGF-β1 by apoptosis in human following loss of (9Sachsenmeier K.F. Sheibani N. Schlosser S.J. Allen-Hoffmann B.L. J. Biol. Chem. 1996; 271: 5-8Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar). of with TGF-β1 DNA Moreover, inhibition of TGF-β1 by to TGF-β1 DNA fragmentation following Thus, TGF-β1 possesses the ability to both and effects in cell and the cellular responses are for of the that TGF-β1 cell survival in cell types, we were in the downstream intracellular pathways for protective effects of TGF-β1 in that TGF-β1 is of MAPK-dependent pathways in cells have been activation of by TGF-β1 has been in epithelial cells and is associated with growth effects of TGF-β1 M.T. Frey R.S. Zipfel P.A. Buard A. Cook S.J. McCormick F. Mulder K.M. J. Biol. Chem. 1996; 271: 22368-22375Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar). In cell types, including and cell TGF-β1 has been shown to JNK/SAPK, and dominant-negative of components of the pathway TGF-β signaling A. Djelloul S. Chastre E. Davis R. Gespach C. J. Biol. Chem. 1997; 272: 1429-1432Abstract Full Text Full Text PDF PubMed Scopus (273) Google Scholar). We examined TGF-β1 is of MAPK in macrophages and TGF-β1 rescue from serum deprivation-induced apoptosis via the MAPK-dependent pathway. activity by two phosphorylation of ERK1/ERK2 determined by MAPK that the tyrosine of activity determined by in kinase assay. with MAPK to for the activated MAPK, of in of a known determined that the show that ERK1/ERK2 activated of with exogenous TGF-β1 in cultured RAW 264.7 cells, and this activation up to 4 h the in phosphorylation of is with of ERK1/ERK2 In we that TGF-β1 to or p38 this time that TGF-β1 is of rapidly the not the or p38 pathways, in RAW 264.7 macrophages The pathway is the MAPK pathway by growth factor and implicated in the regulation of cellular and differentiation (18Davis R.J. Trends Biochem. Sci. 1994; 19: 470-473Abstract Full Text PDF PubMed Scopus (917) Google Scholar, J.M. E. T. J. Nature. 1994; PubMed Scopus Google Scholar). for in the of apoptosis has been by studies in 1 a of the family of cytokines, is a potent survival factor of apoptosis in via the activation of an signaling pathway that MEKs K. J. M. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). We determined the pathway involved in the apoptotic rescue of macrophages by TGF-β1, two to the signaling pathway. transfection studies with the dominant-negative mutant MAPK (ERK2) in RAW 264.7 cells in the of TGF-β1 effects To further support we utilized an which MEK1 activation by downstream activation of does not inhibit or p38 protein kinase In the has been shown to have effect on kinases, including kinase, protein kinase and and threonine kinases L. A.J. Proc. Natl. Acad. Sci. U. S. A. 1995; PubMed Scopus Google Scholar, L. T. S.J. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar, A. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar). In our prevented the effects of TGF-β1 in serum-deprived macrophages and further for the of the pathway in the survival of TGF-β1 studies our that MAPK-dependent pathways are for the survival effects of TGF-β1 have been for in cells and growth factor the survival of cells via activation of the pathway to mediate and initiate rescue from apoptosis by serum deprivation, and activation with inhibition of MAPK (ERK) are required for and apoptosis M. J. Davis R.J. M.E. Science. 1995; 270: PubMed Scopus Google Scholar). The MAPK pathways have also been to be for effects on survival of serum-deprived and MAPK activation by transfection of a dominant-negative mutant or by with inhibited the survival effect of K. J. M. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). Furthermore, in the we in the presence of induction of apoptosis in RAW 264.7 cells upon of the MAPK signaling pathways either by a dominant-negative mutant of MAPK (ERK) or by MEK1 Thus, on our studies and those is that the MAPKs (ERK) a pathway by to cell It be of to determine MAPK-dependent signaling pathways to cell survival, and the may have is by cells and a critical process in regulation of response, or of inflammatory A. J. 1998; PubMed Scopus Google Scholar). The of TGF-β1 in the regulation of is well by the that TGF-β have and inflammatory I. S. R.J. M. R. C. N. T. Nature. 1992; PubMed Scopus Google Scholar, A. M. J.M. S. Proc. Natl. Acad. Sci. U. S. A. 1993; PubMed Scopus Google Scholar). We have identified TGF-β1 as an inhibitor of apoptosis in cultured macrophages and may serve as a cell survival factor via the MAPK-dependent pathway. This macrophages with a cellular mechanism to be from and cell death, a process that be critical in the of of macrophages is required to their of and of or cells, including lymphocytes, that have apoptosis, and that survival to inflammatory