MEKK-1, a Component of the Stress (Stress-activated Protein Kinase/c-Jun N-terminal Kinase) Pathway, Can Selectively Activate Smad2-mediated Transcriptional Activation in Endothelial Cells

Smad proteins are essential components of the intracellular signaling pathways utilized by members of the transforming growth factor-β (TGF-β) superfamily of growth factors. Certain Smad proteins (e.g. Smad1, -2, and -3) can act as regulated transcriptional activators, a process that involves phosphorylation of these proteins by activated TGF-β superfamily receptors. We demonstrate that the intracellular kinase mitogen-activated protein kinase kinase kinase-1 (MEKK-1), an upstream activator of the stress-activated protein kinase/c-Jun N-terminal kinase pathway, can participate in Smad2-dependent transcriptional events in cultured endothelial cells. A constitutively active form of MEKK-1 but not mitogen-activated protein kinase kinase-1 (MEK-1) or TGF-β-activated kinase-1, two distinct intracellular kinases, can specifically activate a Gal4-Smad2 fusion protein, and this effect correlates with an increase in the phosphorylation state of the Smad2 protein. These effects do not require the presence of the C-terminal SSXS motif of Smad2 that is the site of TGF-β type 1 receptor-mediated phosphorylation. Activation of Smad2 by active MEKK-1 results in enhanced Smad2-Smad4 interactions, nuclear localization of Smad2 and Smad4, and the stimulation of Smad protein-transcriptional coactivator interactions in endothelial cells. Overexpression of Smad7 can inhibit the MEKK-1-mediated stimulation of Smad2 transcriptional activity. A physiological level of fluid shear stress, a known activator of endogenous MEKK-1 activity in endothelial cells, can stimulate Smad2-mediated transcriptional activity. These data demonstrate a novel mechanism for activation of Smad protein-mediated signaling in endothelial cells and suggest that Smad2 may act as an integrator of diverse stimuli in these cells. Smad proteins are essential components of the intracellular signaling pathways utilized by members of the transforming growth factor-β (TGF-β) superfamily of growth factors. Certain Smad proteins (e.g. Smad1, -2, and -3) can act as regulated transcriptional activators, a process that involves phosphorylation of these proteins by activated TGF-β superfamily receptors. We demonstrate that the intracellular kinase mitogen-activated protein kinase kinase kinase-1 (MEKK-1), an upstream activator of the stress-activated protein kinase/c-Jun N-terminal kinase pathway, can participate in Smad2-dependent transcriptional events in cultured endothelial cells. A constitutively active form of MEKK-1 but not mitogen-activated protein kinase kinase-1 (MEK-1) or TGF-β-activated kinase-1, two distinct intracellular kinases, can specifically activate a Gal4-Smad2 fusion protein, and this effect correlates with an increase in the phosphorylation state of the Smad2 protein. These effects do not require the presence of the C-terminal SSXS motif of Smad2 that is the site of TGF-β type 1 receptor-mediated phosphorylation. Activation of Smad2 by active MEKK-1 results in enhanced Smad2-Smad4 interactions, nuclear localization of Smad2 and Smad4, and the stimulation of Smad protein-transcriptional coactivator interactions in endothelial cells. Overexpression of Smad7 can inhibit the MEKK-1-mediated stimulation of Smad2 transcriptional activity. A physiological level of fluid shear stress, a known activator of endogenous MEKK-1 activity in endothelial cells, can stimulate Smad2-mediated transcriptional activity. These data demonstrate a novel mechanism for activation of Smad protein-mediated signaling in endothelial cells and suggest that Smad2 may act as an integrator of diverse stimuli in these cells. The transforming growth factor-β (TGF-β) 1The abbreviations used are:TGF-β, transforming growth factor-β; MAPK, mitogen-activated protein kinase; ERK, extracellular signal-related kinase; SAPK, stress-activated protein kinase; JNK c-Jun N-terminal kinase, AP-1, activating protein-1; TAK-1, TGF-β-activated kinase-1; BAEC, bovine aortic endothelial cells; NF-kB, nuclear factor-kappa B; MEK-1, MAPK kinase-1; MEKK-1, MEK kinase-1; CBP, CREB-binding protein; CRE, cyclic AMP response element; LSS, laminar shear stress; TβRI, TGF-β type I receptor. superfamily of growth factors and cytokines is involved in a wide variety of physiological and pathophysiological processes in the cardiovascular system, and the signaling mechanisms utilized by this class of effectors are rapidly being elucidated. The discovery of Smad proteins and the demonstration that they can mediate many of the transcriptional effects of these growth factors has been an important advance (1Baker J.C. Harland R.M. Curr. Opin. Genet. & Dev. 1997; 7: 467-473Crossref PubMed Scopus (96) Google Scholar, 2Massague J. Cell. 1996; 85: 947-950Abstract Full Text Full Text PDF PubMed Scopus (829) Google Scholar, 3Wrana J.L. Miner. Electrolyte Metab. 1998; 24: 120-130Crossref PubMed Scopus (82) Google Scholar). The central roles of these proteins in mediating TGF-β responses in cells is highlighted by the demonstration that mutations in Smads 2, 3, and 4 have been causally linked to specific malignancies, and disruption of the Smad2 and Smad4 genes in mice results in early embryonic lethality (4Waldrip W.R. Bikoff E.K. Hoodless P.A. Wrana J.L. Robertson E.J. Cell. 1998; 92: 797-808Abstract Full Text Full Text PDF PubMed Scopus (397) Google Scholar, 5Zhou S. Buckhaults P. Zawel L. Bunz F. Riggins G. Le Dai J. Kern S.E. Kinzler K.W. Vogelstein B. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 2412-2416Crossref PubMed Scopus (140) Google Scholar). As the detailed molecular mechanisms of Smad protein signaling have emerged a number of functional interactions between these proteins and other signaling pathways have been reported. For instance, recent work has demonstrated that the classic mitogen-activated protein kinase pathway (MAPK/ERK) can negatively regulate bone morphogenic protein/Smad1-dependent transcriptional responses. This appears to occur as a result of the phosphorylation of Smad1 by a member of the Erk kinases and subsequent translocation of Smad1 out of the nucleus (6Kretzschmar M. Doody J. Massague J. Nature. 1997; 389: 618-622Crossref PubMed Scopus (775) Google Scholar). In contrast to this inhibitory effect, the stress-activated protein kinase pathway (i.e. the SAPK/JNK pathway) has been implicated as a positive regulator of certain Smad-dependent effects. Previous data from several groups have documented the importance of AP-1 and related transcriptional effectors in some TGF-β-mediated transcriptional responses, and a recent report demonstrated a direct functional interaction between Smad3 and c-Fos/c-Jun in mediating TGF-β-dependent transcription (7Chung K.Y. Agarwal A. Uitto J. Mauviel A. J. Biol. Chem. 1996; 271: 3272-3278Abstract Full Text Full Text PDF PubMed Scopus (316) Google Scholar, 8Zhang Y. Feng X.H. Derynck R. Nature. 1998; 394: 909-913Crossref PubMed Scopus (688) Google Scholar). Recently, signals derived from growth factor receptors containing tyrosine kinase activities were shown to be capable of modulating Smad-dependent effects. This was suggested to occur as a result of activation of a kinase downstream of MEK-1, an upstream activator of the classic MAPK/ERK kinase pathway, resulting in the phosphorylation of Smad2 (9de Caestecker M.P. Parks W.T. Frank C.J. Castagnino P. Bottaro D.P. Roberts A.B. Lechleider R.J. Genes Dev. 1998; 12: 1587-1592Crossref PubMed Scopus (254) Google Scholar). In addition, a variety of other kinases have been implicated in TGF-β signaling, such as TAK-1 and TAB, although their precise roles have not been elucidated (10Shibuya H. Yamaguchi K. Shirakabe K. Tonegawa A. Gotoh Y. Ueno N. K. K. 1996; PubMed Scopus Google Scholar, K. Yamaguchi K. H. K. S. Gotoh Y. K. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, K. Shirakabe K. H. K. Ueno N. K. PubMed Scopus Google Scholar). these data that may Smad signaling in cells and to mechanisms by signals derived from members may TGF-β superfamily responses. these data suggest that Smad proteins may be involved in the of diverse signals in cells. In this report demonstrate that MEKK-1, a MAPK kinase kinase that is an upstream activator of the SAPK/JNK pathway, is capable of activating Smad2-dependent transcriptional activity of TGF-β in cultured endothelial cells. These data demonstrate a functional interaction between the SAPK/JNK and Smad signaling pathways and suggest that Smad protein signaling may be by MEKK-1 or related kinases in endothelial cells. bovine aortic endothelial cells were as and cultured in with bovine and J. Y. R. C.J. Proc. Natl. Acad. Sci. U. S. A. 1997; PubMed Scopus Google Scholar). These were utilized cells were in the The Smad protein fusion and fusion have been Proc. Natl. Acad. Sci. U. S. A. 1998; 95: PubMed Scopus Google Scholar). The activator was by MEKK-1 by and activated TAK-1 by The active MEKK-1, MEK-1, and protein kinase A were from The activated MEKK-1 of of The activated of the that has The c-Jun and fusion proteins of of c-Jun and of to the The CRE, AP-1, and of AP-1 or upstream of a and The Smad2 and have been Proc. Natl. Acad. Sci. U. S. A. 1998; 95: PubMed Scopus Google Scholar). For the a the and these were the For cells were and for The cells were to in containing of and activity were results are as activity to activity from kinase and are of A utilized of and of active kinase (e.g. MEKK-1 and and of were by the of the used in the and were from The MEKK-1, and were from were in with and were 4 were to by and with as in the proteins were with a to and with cells were as to and in containing for For the TGF-β active TGF-β & was for the The cells were and with as were a and to and was with were to for protein were as The were and in for and with for 1 with the were for 1 The were and with to The were with a and with a were to a laminar shear a that has been in and is a for cultured cells to fluid stimuli J. Proc. Natl. Acad. Sci. U. S. A. 1996; PubMed Scopus Google Scholar, J. G. 1998; PubMed Scopus Google Scholar). For these the were as and to that were to the for was by a a of as utilized the as the the of kinases in the of Smad signaling in endothelial cells, the of constitutively activated of MEK-1, MEKK-1, and TAK-1 to regulate two TGF-β the activator and is an activator of the classic MAPK/ERK pathway, and MEKK-1 is an activator of the or SAPK/JNK pathway R.J. Dev. PubMed Scopus Google Scholar, B. R.M. Y. K. K. Dev. PubMed Scopus Google Scholar). TAK-1 is a kinase that has been implicated in TGF-β signaling and is capable of activating components of the SAPK/JNK pathway, but precise is K. Shirakabe K. H. K. Ueno N. K. PubMed Scopus Google Scholar). In in cultured bovine aortic endothelial cells a of active kinase to of 1 to was to be to activate and these MEKK-1 was capable of activating the and of active or active or type were to activate these although active TAK-1 stimulate the not 1 the response of the and to of active MEKK-1, active MEK-1, or a constitutively active TGF-β are by the active and active MEKK-1 but not by active these kinases are in with the activated TGF-β MEKK-1 appears to stimulate the activity of in a to the TGF-β has the mechanisms of these effects in the was with active or active MEKK-1, and the effects of of a form of MEKK-1 or an inhibitory Smad protein, was As shown in 1 the of by the active TGF-β was by the MEKK-1 and was by of the of by active MEKK-1 was by of MEKK-1 and 1 is a of the of the activated kinases utilized in these the level of used a level of activated MEKK-1 or protein that of the endogenous protein, and the of the two active kinases and these results suggest that transcriptional of the and by the active the of MEKK-1 as as Smad In addition, the that Smad7 can active MEKK-1-mediated stimulation of these that Smad proteins are a in the MEKK-1-mediated transcriptional this utilized a transcriptional We have shown that this Smad-dependent activation of transcription in cultured endothelial cells Proc. Natl. Acad. Sci. U. S. A. 1998; 95: PubMed Scopus Google Scholar). aortic endothelial cells were with fusion proteins between the and or C-terminal of and with a and constitutively activated of MEKK-1 or As shown in MEKK-1 Smad2-dependent transcription in this The level of activity in the of MEKK-1 a of endogenous TGF-β activation in the endothelial Smad4 a level of transcriptional activity in this system, and this is not enhanced in the presence of containing the C-terminal with the of these proteins and demonstrated of transcriptional activity and were by This is with data that the transcriptional activation is the C-terminal of the Smad protein and that MEKK-1 can stimulate and transcription in the of the inhibitory In contrast to Smad2 and Smad4, Smad7 demonstrated or transcriptional activity in endothelial cells. of a constitutively activated form of not stimulate the transcriptional activity of Smad in this that the MEKK-1-mediated stimulation of transcription is by of the MEKK-1 or these results that MEKK-1 appears capable of Smad2-dependent transcriptional activity in and that Smad7 can with this MEKK-1 has been to the activity of a number of pathways in to the SAPK/JNK pathway such as and events M. M. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: PubMed Scopus Google Scholar, Proc. Natl. Acad. Sci. U. S. A. 1998; 95: PubMed Scopus Google Scholar, Proc. Natl. Acad. Sci. U. S. A. 1998; 95: PubMed Scopus Google Scholar). the of endothelial system, a number of to the of the MEKK-1-mediated from endothelial cells active MEKK-1 to stimulate or and of a to TGF-β in the of the to inhibit the activity of active not inhibit MEKK-1-mediated stimulation of Smad-dependent transcription not These results that MEKK-1 is not the of TGF-β can act in a that MEKK-1 activation of Smad2 and Smad4 was not the result of signaling or stimulation of the transcriptional in this system, the response of a of and transcriptional As shown in constitutively activated kinases and demonstrated a of activation these in MEKK-1 a an was but to MEKK-1 was to stimulate a as with a constitutively activated form of protein kinase a known activator of transcription of active MEKK-1 appears to be the of in this endothelial the of transcription factor activation in system, the of active MEKK-1 and to stimulate the activity of fusion between the and the activation of the transcription factors and and MEKK-1 the transcriptional activity of was a activator of in active activated but not with the of as an activator of the classic MAPK of these kinases a effect the transcriptional activity of the fusion protein. these data demonstrate that in cultured endothelial cells, constitutively activated of MEKK-1 and demonstrate a of and transcription factor activation that is and these MEKK-1 appears capable of Smad2-dependent a of Smad signaling that involves phosphorylation of certain Smad proteins (e.g. a of C-terminal the SSXS by the kinase in TGF-β type 1 receptors S. M. H. L. Wrana J.L. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, S. K. U. P. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, L. Massague J. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, R. Genes Dev. 1998; 12: PubMed Scopus Google Scholar). the of this C-terminal SSXS motif of Smad2 in the transcriptional response to active MEKK-1 two Gal4-Smad2 fusion and that these We have shown that the Smad2 is to TGF-β in BAEC, the Smad2 transcriptional activation Proc. Natl. Acad. Sci. U. S. A. 1998; 95: PubMed Scopus Google Scholar). these were with a constitutively activated form of MEKK-1, the Smad2 was not In a level of transcriptional activity that was enhanced by MEKK-1 in stimulation of Smad2 MEKK-1 stimulation of Smad2 transcriptional activity with a in phosphorylation a of in were with Smad2 with constitutively activated of the TGF-β type I MEKK-1, or and in the presence of As shown in Smad2 demonstrated a level of phosphorylation In the presence of TGF-β or active TβRI, the phosphorylation state of Smad2 although the TGF-β results in a level of Smad2 phosphorylation in this This is in with data the of the TGF-β type I kinase in the phosphorylation of Smad2 S. M. H. L. Wrana J.L. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). In the presence of MEKK-1, the phosphorylation state of Smad2 as with or the active Smad2 phosphorylation. the MEKK-1-mediated increase in the phosphorylation state of Smad2 the SSXS motif known to be the for the TGF-β type I the phosphorylation of the Smad2 in the SSXS motif has been As with type was is a but level of phosphorylation. In contrast to type the phosphorylation state of was not by TGF-β or of the active but is enhanced by of active These results suggest that MEKK-1 activity can result in the phosphorylation of Smad2 by MEKK-1 or a to be and that this phosphorylation can occur a site or distinct from the C-terminal SSXS motif that is the site of type 1 phosphorylation. the of active MEKK-1 to stimulate the transcriptional activity of and A and 4 the of phosphorylation in the or the C-terminal of the SSXS motif appears to be for the MEKK-1-mediated stimulation of Smad2 demonstrated these data do not some for this site in the type Smad2 protein with active and interactions between Smad2 and Smad4 are to be for nuclear localization and subsequent stimulation of transcriptional events in response to TGF-β (1Baker J.C. Harland R.M. Curr. Opin. Genet. & Dev. 1997; 7: 467-473Crossref PubMed Scopus (96) Google Scholar, 2Massague J. Cell. 1996; 85: 947-950Abstract Full Text Full Text PDF PubMed Scopus (829) Google Scholar, 3Wrana J.L. Miner. Electrolyte Metab. 1998; 24: 120-130Crossref PubMed Scopus (82) Google Scholar). MEKK-1 can regulate interactions, and In the system, interactions are by protein to the a protein to the transcriptional activation of the protein, and these with the interaction between these two proteins results in activation of a by the activation and fusion of Smad2 and Smad4, the of MEKK-1 to regulate interactions in endothelial cells. As shown in this some level of interaction between Smad2 and as as with Smad4, in the of stimulation in with or with This result an between the Smad proteins to and the presence of of TGF-β in the the constitutively activated form of MEKK-1 and Smad2-Smad4 active MEKK-1 not stimulate interactions in this not of active MEK-1, not stimulate the transcriptional activity of Smad2 or Smad4, effect interactions in this endothelial demonstrate interactions in a of Smad2 and Smad4 were with active MEK-1, TAK-1, or MEKK-1 in endothelial cells, and the interactions between Smad2 and Smad4 were by Smad2 and the for As can been in is interaction between these two proteins in this in the of stimulation but in the presence of a constitutively activated form of the TGF-β type I of Smad4 with This is with data TGF-β interaction between these two Smad proteins S. M. H. L. Wrana J.L. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). As shown in active MEKK-1 this interaction between Smad2 and Smad4, active or not stimulate Smad2-Smad4 these These data are with the data and demonstrate that MEKK-1 can and specifically stimulate and Smad2-Smad4 interactions in MEKK-1 of Smad2 and Smad4 interactions to in the localization of these utilized Smad2 or Smad4 was and by As can be in Smad2 and demonstrate in cells, a with a localization of these a constitutively activated form of MEKK-1 is with Smad2 or Smad4, proteins nuclear of active not the of Smad in these cells. that these effects were not the result of of Smad a distinct Smad that is to MEKK-1 transcriptional stimulation As shown in Smad7 is in the presence of active We and have shown that Smad2 and Smad4 are the number of regulated transcriptional that with the transcriptional CREB-binding protein MEKK-1 stimulate Smad2 and Smad4 interactions with CBP, the As shown in MEKK-1 an interaction between Smad2 and the C-terminal of This interaction was specific for Smad2 as MEKK-1 not stimulate interaction between Smad4 and of in this not these results with an derived from endothelial cells Smad and active MEKK-1, or As shown in in the presence of active or active MEKK-1, Smad2 and Smad4 can be demonstrated to with endogenous MEKK-1 in endothelial cells is involved in the of Smad2 the of laminar shear stress, a fluid and a known of endogenous MEKK-1 in endothelial cells S. J. B. M. S. Biol. 1996; PubMed Scopus Google Scholar, H. K. R. J. J. Biol. Chem. 1997; PubMed Scopus Google to stimulate transcriptional activity. As shown in of laminar shear a of the transcriptional activity of the Gal4-Smad2 and this effect be by of the the transcriptional activity of a with work the of this transcription factor by shear in endothelial cells. These data that the of endogenous MEKK-1 is an important in the activation of Smad2 by this in endothelial cells and suggest that Smad proteins may be capable of diverse stimuli in these cells. The discovery of Smad proteins has been a advance in of TGF-β superfamily data suggest that these proteins may with a variety of other signaling pathways in cells and may be involved in the or of other stimuli as (6Kretzschmar M. Doody J. Massague J. Nature. 1997; 389: 618-622Crossref PubMed Scopus (775) Google Scholar, 8Zhang Y. Feng X.H. Derynck R. Nature. 1998; 394: 909-913Crossref PubMed Scopus (688) Google Scholar, Caestecker M.P. Parks W.T. Frank C.J. Castagnino P. Bottaro D.P. Roberts A.B. Lechleider R.J. Genes Dev. 1998; 12: 1587-1592Crossref PubMed Scopus (254) Google Scholar, Lechleider R.J. H. Caestecker M.P. Roberts A.B. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: PubMed Scopus Google Scholar). We have demonstrated that a constitutively active form of MEKK-1 can activate Smad-dependent transcription in cultured endothelial cells in the of TGF-β MEKK-1 activation of Smad2-mediated transcription with an increase in phosphorylation of Smad2 in the of the C-terminal SSXS motif of Smad2 that is the site of TGF-β the that MEKK-1 activation of Smad2 can occur of Activation of Smad2 by MEKK-1 in an enhanced interaction with Smad4, nuclear localization of Smad2 and Smad4, and a stimulation of coactivator These data a novel mechanism for the of Smad protein signaling in endothelial cells. The functional interactions between the classic and kinase pathways and Smad proteins are to be Previous work has demonstrated that pathways can be implicated in TGF-β transcriptional responses A. M. A. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, A. S. R. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, 1997; Google Scholar). and A. M. A. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, A. S. R. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google that a form of MEKK-1 inhibit TGF-β-mediated of the in cells, and this that MEKK-1 inhibit and Y. Feng X.H. Derynck R. Nature. 1998; 394: 909-913Crossref PubMed Scopus (688) Google demonstrated a direct interaction between and c-Jun and two transcription factors that are the of the These data suggest that are important interactions between Smad proteins and the SAPK/JNK pathway in the of TGF-β results that MEKK-1, a in this pathway, can specifically stimulate Smad2-mediated transcription suggest an interaction between these growth factor and growth factor that tyrosine kinases have been to activate Smad2-mediated signaling of This effect was demonstrated to be to a phosphorylation Smad2 but not to require the presence of Smad4 (9de Caestecker M.P. Parks W.T. Frank C.J. Castagnino P. Bottaro D.P. Roberts A.B. Lechleider R.J. Genes Dev. 1998; 12: 1587-1592Crossref PubMed Scopus (254) Google Scholar). are with a Smad2 is the of MEKK-1 or a downstream kinase, and this Smad2 to with Smad4, to the with the transcriptional and activate In this the events downstream of Smad2 activation by active MEKK-1 to by TGF-β MEKK-1-mediated stimulation of Smad2 may be an or mechanism of activation of transcriptional events in endothelial cells. The MEKK-1 stimulation of Smad2-dependent transcription is to the direct of this or downstream kinase Smad2 that to transcriptional between AP-1 and Smad2 have demonstrated a in the phosphorylation state of Smad2 in active MEKK-1 cells. this correlates with the of MEKK-1 to stimulate the transcriptional activity of a form of Smad2 that is not a for TGF-β type 1 receptor-mediated phosphorylation In addition, of active TAK-1 this kinase activate transcription of fusion proteins or an AP-1 not activate Smad2-mediated transcription not activation of Smad2-mediated transcription and transcription can be in this endothelial active MEKK-1 Smad2 interactions with and with Smad4 and CBP, but not stimulate Smad4 interactions or interactions in the endothelial and and data not these data suggest that Smad2 is a of this novel intracellular A of these is the of constitutively activated of signaling kinases that can be with or effects. the MEKK-1-mediated activation is active MEK-1, a distinct upstream kinase in the MAPK pathway, or active TAK-1, a kinase implicated in TGF-β signaling, to demonstrate the to activate Smad2 as activated TAK-1 was as a TGF-β-activated kinase and has been to activate the TGF-β activator in cells K. Shirakabe K. H. K. Ueno N. K. PubMed Scopus Google Scholar). In endothelial cells in this activation of active TAK-1 and these activation of a variety of other such as the and active TAK-1 was to activate an in endothelial cells not with data the of this kinase to stimulate JNK activity K. Yamaguchi K. H. K. S. Gotoh Y. K. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). these not Smad protein active activate transcription but not Smad-dependent transcription in although these results do not roles for TAK-1 or in signaling, were to demonstrate stimulation of signaling by these kinases in endothelial cells. the of endogenous MEKK-1 is involved in Smad protein-mediated signaling, utilized a form of the protein to inhibit the of the endogenous As shown in the MEKK-1 can inhibit TGF-β-mediated transcriptional that endogenous MEKK-1 is involved in this These data are with data the of this kinase in TGF-β signaling A. S. R. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). the of other of endogenous MEKK-1 to Smad signaling in endothelial cells, the cells with a fluid laminar shear stress, This has been demonstrated to activation of MEKK-1 in endothelial cells in S. J. B. M. S. Biol. 1996; PubMed Scopus Google Scholar, H. K. R. J. J. Biol. Chem. 1997; PubMed Scopus Google Scholar). these a stimulation of Smad2-mediated transcriptional activity that was by of the In the response to a distinct activator of MEKK-1, to stimulation of Smad2-mediated transcription not these data suggest that endogenous MEKK-1 is a in Smad2-mediated transcriptional activation in endothelial cells and that the in MEKK-1 is activated is to be an important of to Smad protein The of Smad7 to inhibit MEKK-1-mediated stimulation of Smad2-dependent transcriptional activation to a novel for this inhibitory We have demonstrated that Smad7 is by such as laminar shear in endothelial cells and can to the activated type 1 TGF-β and inhibit to Smad2 J. Y. R. C.J. Proc. Natl. Acad. Sci. U. S. A. 1997; PubMed Scopus Google H. S. Y. J. Wrana J.L. Cell. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). In the of active MEKK-1 endothelial cells, Smad7 may be an mechanism to with intracellular kinases and their to Smad7 may be an important of between stimuli such as fluid shear and factor stimuli such as TGF-β and related in endothelial cells J. 1997; PubMed Scopus Google Scholar). In have demonstrated that Smad2-mediated transcriptional activation can be by of an active form of These data with data from other groups suggest that mechanisms may to Smad protein signaling in cells and that this important of intracellular signaling may be involved in TGF-β superfamily the many stimuli that have been demonstrated to activate the SAPK/JNK pathway and MEKK-1 R.J. Dev. PubMed Scopus Google Scholar, S. J. B. M. S. Biol. 1996; PubMed Scopus Google Scholar, S. Y. H. Y. K. K. R. Y. J. PubMed Scopus Google Smad proteins may be involved in modulating the response to diverse signals from effectors such as growth to stimuli such as As this class of signaling proteins may participate in the of processes such as and We and for and and for