Induction of Early Growth Response-1 Gene Expression by Calmodulin Antagonist Trifluoperazine through the Activation of Elk-1 in Human Fibrosarcoma HT1080 Cells

Abstract

The early growth response gene-1 (Egr-1) is a transcription factor that plays an important role in cell growth and differentiation. It has been known that Egr-1 expression is down-regulated in many types of tumor tissues, including human fibrosarcoma HT1080 cells, and introduction of the Egr-1gene into HT1080 cells inhibits cell growth and tumorigenic potential. Trifluoperazine (TFP), a phenothiazine class calmodulin antagonist, is known to inhibit DNA synthesis and cell proliferation and potentially important in antitumor activities. To understand the regulatory mechanism of Egr-1, we investigated the effect of TFP on expression of Egr-1 in HT1080 cells. Herein, we report thatEgr-1 expression was increased by TFP in synergy with serum at the transcriptional level. Both the Ca2+/calmodulin-dependent protein kinase II inhibitor KN62 and the calcineurin inhibitor cyclosporin A enhanced TFP-dependent increase of Egr-1, suggesting that the Ca2+/calmodulindependent pathway plays a role in regulation of Egr-1 expression in HT1080 cells. The TFP-stimulated increase of the Egr-1 protein was preferentially inhibited by the MEK-specific inhibitor PD98059. In addition, activation of human Egr-1 promoter and the transcriptional activation of the ternary complex factor Elk-1 induced by TFP were inhibited both by pretreatment of PD98059 and by expression of the dominant-negative RasN17. These results indicate that the Ras/MEK/Erk/Elk-1 pathway is necessary for TFP-inducedEgr-1 expression. We propose that the calmodulin antagonist TFP stimulates Egr-1 gene expression by modulating Ras/MEK/Erk and activation of the Elk-1 pathway in human fibrosarcoma HT1080 cells. The early growth response gene-1 (Egr-1) is a transcription factor that plays an important role in cell growth and differentiation. It has been known that Egr-1 expression is down-regulated in many types of tumor tissues, including human fibrosarcoma HT1080 cells, and introduction of the Egr-1gene into HT1080 cells inhibits cell growth and tumorigenic potential. Trifluoperazine (TFP), a phenothiazine class calmodulin antagonist, is known to inhibit DNA synthesis and cell proliferation and potentially important in antitumor activities. To understand the regulatory mechanism of Egr-1, we investigated the effect of TFP on expression of Egr-1 in HT1080 cells. Herein, we report thatEgr-1 expression was increased by TFP in synergy with serum at the transcriptional level. Both the Ca2+/calmodulin-dependent protein kinase II inhibitor KN62 and the calcineurin inhibitor cyclosporin A enhanced TFP-dependent increase of Egr-1, suggesting that the Ca2+/calmodulindependent pathway plays a role in regulation of Egr-1 expression in HT1080 cells. The TFP-stimulated increase of the Egr-1 protein was preferentially inhibited by the MEK-specific inhibitor PD98059. In addition, activation of human Egr-1 promoter and the transcriptional activation of the ternary complex factor Elk-1 induced by TFP were inhibited both by pretreatment of PD98059 and by expression of the dominant-negative RasN17. These results indicate that the Ras/MEK/Erk/Elk-1 pathway is necessary for TFP-inducedEgr-1 expression. We propose that the calmodulin antagonist TFP stimulates Egr-1 gene expression by modulating Ras/MEK/Erk and activation of the Elk-1 pathway in human fibrosarcoma HT1080 cells. calmodulin-dependent protein kinase trifluoperazine ternary complex factor Dulbecco's modified Eagle's medium 4-morpholinepropanesulfonic acid kilobase(s) glyceraldehyde-3-phosphate dehydrogenase polymerase chain reaction cytomegalovirus phorbol 12-myristate 13-acetate chlorpromazine serum response element protein kinase C mitogen-activated protein kinase extracellular signal-regulated kinase MAPK/ERK kinase c-Jun N-terminal kinase kinase suppressor of Ras Ca2+ is an important intracellular messenger in many biological processes. Calmodulin is a ubiquitous Ca2+-binding protein that acts as a Ca2+mediator (1Cheung W.Y. Science. 1980; 207: 19-27Crossref PubMed Scopus (1841) Google Scholar). Ca2+-bound calmodulin regulates the activities of a large number of enzymes, including calmodulin-dependent protein kinases (CaMK)1 such as CaMK-II and CaMK-IV. Calmodulin is involved in the Ca2+-mediated regulation of gene expression and in the regulation of cellular proliferation process, including DNA synthesis and cell cycle progression (2Means A.R. Dedman J.R. Nature. 1980; 285: 73-77Crossref PubMed Scopus (711) Google Scholar, 3Hickie R.A. Wei J.-W. Blyth L.M. Wong D.Y.W. Klaassen D. Can. J. Biochem. Cell Biol. 1983; 61: 934-941Crossref PubMed Scopus (73) Google Scholar, 4Lu K.P. Means A.R. Endocrin. Rev. 1993; 14: 40-58Crossref PubMed Scopus (268) Google Scholar, 5Schulman H. Curr. Opin. Cell Biol. 1993; 5: 247-253Crossref PubMed Scopus (173) Google Scholar, 6Lev S. Moreno H. Martinez R. Canoll P. Peles E. Musacchio J.M. Plowman G.D. Rudy B. Schlessinger J. Nature. 1995; 376: 737-745Crossref PubMed Scopus (1242) Google Scholar). It has been reported that the calmodulin level is elevated in several tumor cell lines (3Hickie R.A. Wei J.-W. Blyth L.M. Wong D.Y.W. Klaassen D. Can. J. Biochem. Cell Biol. 1983; 61: 934-941Crossref PubMed Scopus (73) Google Scholar, 7Wei J.-W. Hickie R.A. Biochem. Biophys. Res. Commun. 1981; 100: 1562-1568Crossref PubMed Scopus (48) Google Scholar). Moreover, in vivo treatment with calmodulin antagonists has been shown to reduce tumor size (8MacNeil S. Griffin M. Cooke A.M. Pettett N.J. Dawson R.A. Owen R. Blackburn G.M. Biochem. Pharmacol. 1988; 37: 1717-1723Crossref PubMed Scopus (44) Google Scholar), indicating that calmodulin plays an important role in control of cell growth. It is now known that calmodulin antagonists are cytotoxic against tumor cells and can restore sensitivity to drug-resistant cells, thus addressing the possibility that calmodulin antagonists may be valuable chemotherapeutic agents in the treatment of certain cancers (9Durham A.C. Walton J.M. Biosci. Rep. 1982; 2: 15-30Crossref PubMed Scopus (103) Google Scholar, 10Hait W.N. Lazo J.S. J. Clin. Oncol. 1986; 4: 994-1012Crossref PubMed Scopus (127) Google Scholar). However, little information is available regarding the mechanisms responsible for regulation of cell growth by calmodulin antagonists. Trifluoperazine (TFP) is a phenothiazine derivative antipsychotic drug. TFP is a well known calmodulin antagonist that has been used for studying the function of calmodulin (11Weiss B. Levin R.M. Adv. Cyclic. Nucleotide Res. 1978; 9: 285-303PubMed Google Scholar, 12Osborn M. Weber K. Exp. Cell. Res. 1980; 130: 484-488Crossref PubMed Scopus (85) Google Scholar). Previous reports have demonstrated that TFP inhibits DNA synthesis and cell proliferation and, thereby, is potentially an important antitumor agent, as well as having antipsychotic properties (13Naftalovich S. Yefenof E. Eilam Y. Cancer Chemother. Pharmacol. 1991; 28: 384-390Crossref PubMed Scopus (18) Google Scholar). The product of the early growth response gene Egr-1 (14Sukhatme V.P. Cao X. Chang L.C. Tsai-Morris C.-H. Stamenkovich D. Ferreira P.C.P. Cohen D.R. Edward S.A. Shows T.B. Curran T. LeBeau M.M. Adamson E.D. Cell. 1988; 53: 37-43Abstract Full Text PDF PubMed Scopus (1015) Google Scholar), which is also known as NGFI-A (15Milbrandt J. Science. 1987; 238: 797-799Crossref PubMed Scopus (929) Google Scholar), zif268 (16Christy B.A. Lau L.F. Nathans D. Proc. Natl. Acad. Sci. U. S. A. 1988; 85: 7857-7861Crossref PubMed Scopus (569) Google Scholar), krox24 (17Lemaire P. Revelant O. Bravo R. Charnev P. Proc. Natl. Acad. Sci. U. S. A. 1988; 85: 4691-4695Crossref PubMed Scopus (448) Google Scholar), or Tis8 (18Lim R.W. Varnum B.C. Herschman H.R. Oncogene. 1987; 1: 263-270PubMed Google Scholar), is a transcription factor that has three Cys2-His2-type zinc finger-containing DNA binding domains in the C-terminal portion of the molecule. Egr-1 preferentially binds to GC-rich regulatory elements with the consensus sequence of GCGGGGGCG or TCCTCCTCCTCC (16Christy B.A. Lau L.F. Nathans D. Proc. Natl. Acad. Sci. U. S. A. 1988; 85: 7857-7861Crossref PubMed Scopus (569) Google Scholar, 19Sukhatme V.P. J. Am. Soc. Nephrol. 1990; 1: 859-866Crossref PubMed Google Scholar), leading to induction or repression of its target genes. It has been demonstrated thatEgr-1 is important in regulating cell growth, differentiation, and development (20Liu C. Adamson E. Mercola D. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 11831-11836Crossref PubMed Scopus (147) Google Scholar). Expression of Egr-1is significantly reduced in a number of tumor cells (21Levin W.J. Press M.F. Gaynor R.B. Sukhatme V.P. Boone T.C. Reissmann P.T. Figlin R.A. Holmes E.C. Souza L.M. Slamon D.J. Oncogene. 1995; 11: 1261-1269PubMed Google Scholar, 22Huang R.-P. Fan Y. de Belle I. Niemeyer C. Gottardis M.M. Mercola D. Adamson E. Int. J. Cancer. 1997; 72: 102-109Crossref PubMed Scopus (215) Google Scholar), and loss of expression is closely associated with tumor formation in mammalian cells and tissues (22Huang R.-P. Fan Y. de Belle I. Niemeyer C. Gottardis M.M. Mercola D. Adamson E. Int. J. Cancer. 1997; 72: 102-109Crossref PubMed Scopus (215) Google Scholar). On the other hand, stable expression ofEgr-1 inhibited cell proliferation and soft agar growth in NIH3T3 cells transformed with v-sis, indicating thatEgr-1 functions as a tumor suppressor (23Huang R.-P. Liu C. Fan Y. Mercola D. Adamson E. Cancer Res. 1995; 55: 5054-5062PubMed Google Scholar). We examined the effect of TFP on expression of the tumor suppressorEgr-1 in human fibrosarcoma HT1080 cells. Our results revealed that treatment of cells with serum and TFP increased levels of both mRNA and the protein of Egr-1. The increment was associated with the increase of Egr-1 promoter activity through activation of the ternary complex factor (TCF) Elk-1. Dulbecco's modified Eagle's medium (DMEM), fetal calf serum, and LipofectAMINE 2000 were purchased from Life Technologies, Inc. (Gaithersburg, MD). Cyclosporin A, KN62, and ionomycin were obtained from Calbiochem (San Diego, CA). Trifluoperazine, chlorpromazine, and GF109203X were products of RBI (Natick, MA). Antibodies against Egr-1 and ERK were purchased from Santa Cruz Biotechnology (Santa Cruz, CA).Trans-activator plasmid pFA2-Elk1 (amino acids 307–427), which contains the GAL4 DNA binding domain (amino acids 1–147), and the reporter plasmid pFR-Luc, which contains five repeats of GAL4 binding elements and the luciferase gene, were obtained from Stratagene (La Jolla, CA). The pCMV/β-gal plasmid and assay kits for luciferase and β-galactosidase activity were purchased from Promega (Madison, WI). The cDNA probe for Egr-1 was provided by Dr. I. K. Lim of the Ajou University School of Medicine, South Korea. Cells were lysed in 20 mmHEPES, pH 7.2, 1% Triton X-100, 10% glycerol, 150 mmNaCl, 10 μg/ml leupeptin, and 1 mm phenylmethylsulfonyl fluoride (24Lee Y.H. Kim H.S. Pai J.-K. Ryu S.H. Suh P.-G. J. Biol. Chem. 1994; 269: 26842-26847Abstract Full Text PDF PubMed Google Scholar). Protein of were by and to The were with and with the enhanced The was and with for as an In the was to The of Egr-1 and in were by and was to the by and P. Biochem. 1987; Google Scholar). 10 of was on in pH and 1 mm to a by the was by The was at in The used from the and from the The were with for 20 at at for and for at the were from the by in C. Oncogene. 1991; Google from to and to were by in a reaction of human Egr-1 from as a with the and A is by A a which is by was used in The were with the and The were from the and into and of the reporter WI). was by of with the and by into the by The were by DNA HT1080 cells were in with 10% fetal calf Egr-1 promoter cells were in with 10% fetal calf cells into the cells were with of of the Egr-1 promoter and of pCMV/β-gal plasmid LipofectAMINE 2000 to the mammalian expression of and dominant-negative were of Elk-1 pFA2-Elk1 and were into cells. pCMV/β-gal was to the The of DNA was at with an cells were with Cells were of TFP and protein were by three of and of protein was for luciferase and β-galactosidase activities. was a were by a of luciferase activity to β-galactosidase activity obtained from the It has been reported that stable expression of Egr-1 to DNA synthesis and in fibrosarcoma HT1080 cells (23Huang R.-P. Liu C. Fan Y. Mercola D. Adamson E. Cancer Res. 1995; 55: 5054-5062PubMed Google Scholar). We investigated of DNA synthesis by calmodulin antagonists is to a in Egr-1 expression. 12-myristate 13-acetate was used as a cells in the were with TFP for a increase in the of the Egr-1 protein was cells a increase in the Egr-1 protein level the cells were with However, an increase was in cells with with serum and TFP in a increase in the level of Egr-1 expression. calmodulin antagonist chlorpromazine also increased the level of the Egr-1 protein 1 the with revealed that of were in These results indicate that with serum and calmodulin antagonist has a effect on expression of Egr-1 in HT1080 cells. To the effect of TFP on the increase in the Egr-1 expression HT1080 cells were for with serum in the of of The Egr-1 protein was in cells with serum and 10 The protein level was increased at a of TFP the effect of of TFP on cell was examined by the cell was of control that an increase in the Egr-1 protein level to TFP was at with a increase through of TFP the with revealed that of were in was to the increase in the expression level of the Egr-1 protein to TFP at the mRNA level. The mRNA level was used as an Expression of Egr-1 mRNA was increased by treatment with TFP was with results of that the Egr-1 mRNA level was increased at of serum and TFP with a increase at 1 by a To TFP an increase in Egr-1 mRNA at the transcription we a of luciferase reporter of and the of the human Egr-1 promoter C. Oncogene. 1991; Google Scholar). was with pCMV/β-gal for into cells. cells were or with were as in luciferase activity for β-galactosidase The and and increased luciferase to TFP A to which the increased promoter suggesting that is important for the promoter activity These results indicate that TFP gene expression at the transcription level. Calmodulin the of including CaMK-II and we investigated the pathway is involved in TFP-dependent Egr-1 HT1080 cells were in both the and of TFP with the Ca2+ ionomycin and KN62, a inhibitor of to the of Egr-1 and in were by shown in A, ionomycin effect on Egr-1 and TFP-dependent Egr-1 expression was significantly by the of In addition, KN62 and cyclosporin A, a calcineurin enhanced TFP-dependent Egr-1 expression and These results that the pathway regulates Egr-1 expression. It has been reported that calmodulin antagonists protein kinase C activity R. O. B. P. Res. 1997; PubMed Scopus Google and that the stimulates Egr-1 gene induction We investigated the effect of on TFP-dependent Egr-1 expression. HT1080 cells were with of and of serum and that have effect on TFP-dependent Egr-1 expression To the role of the effect of of by treatment with of was examined of was by treatment with 1 was Egr-1 was induced by with of activity is Egr-1 by with serum and TFP with control These results that are involved in TFP-dependent Egr-1 expression. To the pathway involved in the TFP several kinase were kinase inhibitor inhibitor and inhibitor effect on Egr-1 expression to serum and In a inhibited TFP-stimulated Egr-1 expression. the effect of PD98059 was examined of of PD98059 the level of Egr-1 expression to serum and indicating that the is for TFP-dependent Egr-1 expression. To that the pathway to TFP-stimulated activation of cells were with a and a dominant-negative or a of the expression shown in promoter activity was inhibited by dominant-negative or by pretreatment with PD98059. However, the expression of These indicate that the pathway plays a role in TFP-dependent Egr-1 gene expression. To TFP stimulates a target of we examined the of ERK activation in response to serum in HT1080 cells for of and In a control for and with serum were HT1080 cells were for with serum for of ERK was by shown in A, increased of was of serum in In a level of was in HT1080 cells and a increase of was serum that are of serum in HT1080 cells. These results are with reports that HT1080 cells are as tumor cells with to the activation of and R. Y. T. T. H. O. Y. S. H. J. M. Oncogene. PubMed Scopus Google Scholar). that serum and TFP effect on the increase of which was inhibited by pretreatment with PD98059. on we that of is involved in activation of promoter in response to Previous have demonstrated that Ca2+/calmodulin-dependent calcineurin regulates the transcription activation of Elk-1 T. S. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, J. M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). Egr-1 transcription is through a serum response element which binds a complex of the serum response factor and a of the ternary complex factor The Elk-1 K. M. A. Science. PubMed Scopus Google Scholar), S. R. Cell. Full Text PDF PubMed Scopus Google Scholar), and A. A. P. B. 1994; PubMed Scopus Google Scholar, M. P. Y. U. Cell. Biol. 1994; 14: PubMed Scopus Google Scholar, R. J. 1995; 14: PubMed Scopus Google Scholar). The is responsible for the of and Elk-1 by ERK with increased transcription activation P. Science. 1995; 269: PubMed Scopus Google Scholar). To Elk-1 is involved in a that the protein of the DNA binding domain and the activation domain of Elk-1 (amino acids was into cells. pFR-Luc, which contains five repeats of the binding element of the luciferase reporter gene, was also assay of transcription activation in response to cells were with serum and activation of Elk-1 was which was inhibited in a by pretreatment with PD98059 In addition, TFP-stimulated Elk-1 activation was inhibited by expression of dominant-negative Elk-1 which was inhibited by that is necessary for TFP-stimulated Elk-1 results a in which the calmodulin-dependent pathway expression by modulating It is well known that Egr-1 is an response transcription factor that is induced in many cell types by a of growth and A. Sukhatme V.P. Res. Biol. 1995; PubMed Scopus Google Scholar). Egr-1 is to is that thatEgr-1 regulates cell growth. Egr-1 is little or in a number of tumor cells, including and fibrosarcoma HT1080 cells (23Huang R.-P. Liu C. Fan Y. Mercola D. Adamson E. Cancer Res. 1995; 55: 5054-5062PubMed Google Scholar). Expression of mRNA in NIH3T3 cells to an enhanced transformed R.-P. T. D. Mercola D. Adamson E. Oncogene. 1994; 9: Google Scholar), indicating that loss of Egr-1 gene expression is important for tumorigenic potential. On the introduction of Egr-1 into HT1080 fibrosarcoma cells inhibits cell growth and (21Levin W.J. Press M.F. Gaynor R.B. Sukhatme V.P. Boone T.C. Reissmann P.T. Figlin R.A. Holmes E.C. Souza L.M. Slamon D.J. Oncogene. 1995; 11: 1261-1269PubMed Google Scholar, 22Huang R.-P. Fan Y. de Belle I. Niemeyer C. Gottardis M.M. Mercola D. Adamson E. Int. J. Cancer. 1997; 72: 102-109Crossref PubMed Scopus (215) Google Scholar, R.-P. Liu C. Fan Y. Mercola D. Adamson E. Cancer Res. 1995; 55: 5054-5062PubMed Google by induction of growth and the (20Liu C. Adamson E. Mercola D. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 11831-11836Crossref PubMed Scopus (147) Google Scholar, C. J. de Belle I. R.-P. Adamson E. Mercola D. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar), the that Egr-1 a growth suppressor TFP is a calmodulin antagonist that binds to calmodulin and inhibits activities. Calmodulin is a Ca2+-binding protein in cells that plays a role as a Ca2+ (1Cheung W.Y. Science. 1980; 207: 19-27Crossref PubMed Scopus (1841) Google Scholar). that calmodulin is involved in regulation of cellular and calmodulin antagonists the for in the treatment of certain However, the mechanisms responsible for the antitumor activities of calmodulin antagonists to be We that the calmodulin antagonists TFP and gene expression in human fibrosarcoma HT1080 cells. of Egr-1 expression by TFP was in HT1080 cells in cells We also that with serum and TFP Egr-1 expression by transcriptional and We that transcription in HT1080 cells is by and repression can be by treatment with calmodulin antagonists. To the calmodulin-dependent pathway is involved in of Egr-1, we used the KN62 of and cyclosporin A of In the of serum, Egr-1 expression was by treatment with and expression was enhanced by KN62 and cyclosporin A These indicate that Ca2+/calmodulin-dependent protein kinase II and calcineurin Egr-1 expression in HT1080 cells. These are with which have shown that of and are enhanced by of calcineurin with cyclosporin A in the and cells types H. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar, A. M. A. H. Biochem. J. PubMed Scopus Google Scholar). is a protein the control of H. X. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). is the of the pathway in regulating the of transcription factor by Rev. Biochem. 1994; PubMed Scopus Google Scholar). in cells, calcineurin may an important role in the regulation of gene expression in other cell It has been reported that activation of calcineurin inhibits growth of the of transcription factor Elk-1 and plays a role in induction of transcription J. M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). However, to be inhibits Elk-1 activity in HT1080 cells. It has been reported that expression of the Egr-1 gene in response to several and the is through the serum response elements in the of the gene S.A. 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We that and Egr-1 expression was inhibited by a by the inhibitor the inhibitor or the kinase inhibitor A We also that TFP-dependent activation of the Egr-1 promoter was by expression of the dominant-negative of and by pretreatment with PD98059 These indicate that the are necessary to Egr-1 expression to serum and Elk-1 was by treatment with and TFP-stimulated Elk-1 was inhibited by both PD98059 and the dominant-negative TFP TFP acts of at at the level of Elk-1. is that Ca2+/calmodulin-dependent calcineurin is a of Elk-1. T. S. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google and the and J. M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google reported that expression of calcineurin or activation of calcineurin by Ca2+ growth of Elk-1 and that treatment with cyclosporin A the effect of calcineurin on Elk-1 and These results are with the that TFP acts of calcineurin to in of Elk-1. other and are also reported to Elk-1 C. Oncogene. 1991; Google R. J. 1996; PubMed Scopus Google Scholar). the the of and in Elk-1 the of Elk-1 activation by the dominant-negative and PD98059 that calcineurin is the target of is known that the inhibitor PD98059 inhibit or We that the calmodulin antagonist TFP stimulates Egr-1gene induction of the the of the Ca2+/calmodulin-dependent pathway and the of Egr-1 gene expression in HT1080 cells. It has been reported that of the is in a of human and is now that expression plays a role in lines of a role for the activation of the pathway in a R. Y. T. T. H. O. Y. S. H. J. M. Oncogene. PubMed Scopus Google Scholar, H. B. R. A. M. J. P. C. Cell. 1987; Full Text PDF PubMed Scopus Google Scholar). In human fibrosarcoma HT1080 cells, a at of that to has been which may be to cells to R. A. J. PubMed Scopus (85) Google Scholar). loss of Egr-1 expression plays a role in the transformed of HT1080 cells (23Huang R.-P. Liu C. Fan Y. Mercola D. Adamson E. Cancer Res. 1995; 55: 5054-5062PubMed Google and the R. A. J. PubMed Scopus (85) Google Scholar). loss of plays a role in the transformed of HT1080 cells (23Huang R.-P. Liu C. Fan Y. Mercola D. Adamson E. Cancer Res. 1995; 55: 5054-5062PubMed Google and the pathway the transcription activation of Egr-1 is down-regulated in HT1080 cells is possibility is regulation of Egr-1 expression by In several have demonstrated that Ras is involved in mechanisms as of the regulation of J. Biol. Chem. 1991; Full Text PDF PubMed Google Scholar, C. Cell. Biol. 1995; PubMed Google Scholar, M. Oncogene. 1995; Scholar). Cell. Biol. 1996; PubMed Scopus Google reported that expression of Ras regulates gene induction in also that the effect of Ras on Egr-1 and induction by is by pretreatment with cyclosporin A, indicating of calcineurin in T. S. M. J. PubMed Scopus Google reported that a kinase suppressor of Ras growth factor and transcription activation of of the including and the Moreover, that the effect of on the of Elk-1 transcription activation is by of Elk-1 the of on can that plays a role in expression of tumor suppressor Egr-1, in HT1080 cells. In be of to the of in the progression of We the possibility that Egr-1 transcription can be by other that are to Ras expression. Our that TFP as a calmodulin antagonist stimulates induction of tumor suppressorEgr-1 gene expression in the of serum in HT1080 human fibrosarcoma cells. TFP plays a role in modulating through of the Ca2+/calmodulin-dependent It be of to Elk-1 activation of transcription through is the pathway by which TFP expression of genes. The of calmodulin antagonists may a to of growth.