An Inducible Pathway for Degradation of FLIP Protein Sensitizes Tumor Cells to TRAIL-induced Apoptosis

Abstract

TRAIL (Apo2 ligand) is a member of the tumor necrosis factor (TNF) family of cytokines that induces apoptosis. Because TRAIL preferentially kills tumor cells, sparing normal tissues, interest has emerged in applying this biological factor for cancer therapy in humans. However, not all tumors respond to TRAIL, raising questions about resistance mechanisms. We demonstrate here that a variety of natural and synthetic ligands of peroxisome proliferator-activated receptor-γ (PPARγ) sensitize tumor but not normal cells to apoptosis induction by TRAIL. PPARγ ligands selectively reduce levels of FLIP, an apoptosis-suppressing protein that blocks early events in TRAIL/TNF family death receptor signaling. Both PPARγ agonists and antagonists displayed these effects, regardless of the levels of PPARγ expression and even in the presence of a PPARγ dominant-negative mutant, indicating a PPARγ-independent mechanism. Reductions in FLIP and sensitization to TRAIL-induced apoptosis were also not correlated with NF-κB, further suggesting a novel mechanism. PPARγ modulators induced ubiquitination and proteasome-dependent degradation of FLIP, without concomitant reductions in FLIP mRNA. The findings suggest the existence of a pharmacologically regulated novel target of this class of drugs that controls FLIP protein turnover, and raise the possibility of combining PPARγ modulators with TRAIL for more efficacious elimination of tumor cells through apoptosis. TRAIL (Apo2 ligand) is a member of the tumor necrosis factor (TNF) family of cytokines that induces apoptosis. Because TRAIL preferentially kills tumor cells, sparing normal tissues, interest has emerged in applying this biological factor for cancer therapy in humans. However, not all tumors respond to TRAIL, raising questions about resistance mechanisms. We demonstrate here that a variety of natural and synthetic ligands of peroxisome proliferator-activated receptor-γ (PPARγ) sensitize tumor but not normal cells to apoptosis induction by TRAIL. PPARγ ligands selectively reduce levels of FLIP, an apoptosis-suppressing protein that blocks early events in TRAIL/TNF family death receptor signaling. Both PPARγ agonists and antagonists displayed these effects, regardless of the levels of PPARγ expression and even in the presence of a PPARγ dominant-negative mutant, indicating a PPARγ-independent mechanism. Reductions in FLIP and sensitization to TRAIL-induced apoptosis were also not correlated with NF-κB, further suggesting a novel mechanism. PPARγ modulators induced ubiquitination and proteasome-dependent degradation of FLIP, without concomitant reductions in FLIP mRNA. The findings suggest the existence of a pharmacologically regulated novel target of this class of drugs that controls FLIP protein turnover, and raise the possibility of combining PPARγ modulators with TRAIL for more efficacious elimination of tumor cells through apoptosis. TNF-related apoptosis inducing ligand tumor necrosis factor 2-cyano-3,12-dioxooleane-1,9-dien-28-oic acid 15-deoxy-Δ12,14-prostaglandin J2 FLICE-inhibitory protein IκB kinase peroxisome proliferator-activated receptor 1-chloro-3-tosylamido-7-amino-2-heptanone 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide benzyloxycarbonyl fluoromethyl ketone glutathioneS-transferase 4,6-diamidino-2-phenylindole electrophoretic mobility shift assays green fluorescent protein poly(ADP-ribose) polymerase PPAR-response elements ubiquitin-protein isopeptide ligase Considerable interest has emerged in the possibility of exploiting the apoptotic effects of TRAIL1 for the treatment of cancer. TRAIL is a member of the tumor necrosis factor (TNF) family of cytokines that is capable of inducing apoptosis (1Griffith T.S. Lynch D.H. Curr. Opin. Immunol. 1998; 10: 559-563Crossref PubMed Scopus (441) Google Scholar). The apoptosis-inducing receptors for TRAIL include Trail-R1 (DR4) and Trail-R2 (DR5), which are transmembrane type I receptors expressed on the surface of many types of cell. However, TRAIL also binds to non-apoptosis-inducing decoy receptors, which compete with death receptors for ligand and suppress apoptosis, including DcR1, DcR2, and osteoprotegerin (reviewed in Refs. 2Ashkenazi A. Dixit V.M. Science. 1998; 281: 1305-1308Crossref PubMed Scopus (5169) Google Scholar and 3Golstein P. Curr. Biol. 1997; 7: R750-R753Crossref PubMed Google Scholar). Empiric analysis of the effects of TRAIL on normal and malignant cells has provided compelling evidence that recombinant TRAIL protein preferentially induces apoptosis of cancer cells without harming most types of untransformed cells (reviewed in Ref. 2Ashkenazi A. Dixit V.M. Science. 1998; 281: 1305-1308Crossref PubMed Scopus (5169) Google Scholar). When properly prepared and purified, recombinant trimeric TRAIL also lacks significant toxicity in primate species that possess receptors capable of binding human TRAIL (4Ashkenazi A. Pai R.C. Fong S. Leung S. Lawrence D.A. Marsters S.A. Blackie C. Chang L. McMurtrey A.E. Hebert A. DeForge L. Koumenis I.L. Lewis D. Harris L. Bussiere J. Koeppen H. Shahrokh Z. Schwall R.H. J. Clin. Invest. 1999; 104: 155-162Crossref PubMed Scopus (2008) Google Scholar,5Lawrence D. Shahrokh Z. Marsters S. Achilles K. Shih D. Mounho B. Hillan K. Totpal K. DeForge L. Schow P. Hooley J. Sherwood S. Pai R. Leung S. Khan L. Gliniak B. Bussiere J. Smith C.A. Strom S.S. Kelley S. Fox J.A. Thomas D. Ashkenazi A. Nat. Med. 2001; 7: 383-385Crossref PubMed Scopus (636) Google Scholar). Preclinical studies of recombinant TRAIL (extracellular domain) in mice have demonstrated impressive anti-tumor activity and synergy with cytotoxic anticancer drugs (6Bonavida B., Ng, C.P. Jazirehi A. Schiller G. Mizutani Y. Int. J. Oncol. 1999; 15: 793-802PubMed Google Scholar). However, not all tumors respond to TRAIL. This lack of response may be attributed either to unfavorable ratios of death and decoy receptors or because of intracellular resistance mechanisms (3Golstein P. Curr. Biol. 1997; 7: R750-R753Crossref PubMed Google Scholar, 7Pan G., Ni, J. Wei Y.F., Yu, G. Gentz R. Dixit V.M. Science. 1997; 277: 815-818Crossref PubMed Scopus (1383) Google Scholar, 8Sheridan J.P. Marsters S.A. Pitti R.M. Gurney A. Skubatch M. Baldwin D. Ramakrishnan L. Gray C.L. Baker K. Wood W.I. Goddard A.D. Godowski P. Ashkenazi A. Science. 1997; 277: 818-821Crossref PubMed Scopus (1533) Google Scholar, 9Irmler M. Thome M. Hahne M. Schneider P. Hofmann K. Steiner V. Bodmer J.-L. Schröter M. Burns K. Mattmann C. Rimoldi D. French L.E. Tschopp J. Nature. 1997; 388: 190-195Crossref PubMed Scopus (2231) Google Scholar, 10Thome M. Schneider P. Hofmann K. Fickenscher H. Meinl E. Neipel F. Mattmann C. Burns K. Bodmer J.-L. Schroter M. Scaffidi C. Krammer P.H. Peter M.E. Tschopp J. Nature. 1997; 386: 517-521Crossref PubMed Scopus (1146) Google Scholar). With respect to intracellular resistance mechanisms, the FLIP protein has been identified as a blocker of apoptosis induced by TNF family death receptors (reviewed in Ref. 11Krammer P.H. Nature. 2000; 407: 789-795Crossref PubMed Scopus (1407) Google Scholar). FLIP binds to and neutralizes adapter proteins and pro-caspases normally recruited to the cytosolic domains of apoptosis-inducing TRAIL receptors upon ligand stimulation, thus interrupting early steps in TRAIL signaling. Furthermore, overexpression of FLIP protein has been documented in cancers (12Griffith T. Chin W. Jackson G. Lynch D. Kubin M. J. Immunol. 1998; 161: 2833-2840PubMed Google Scholar). PPARγ is a member of the steroid/retinoid superfamily of ligand-activated transcription factors. Agonistic ligands of PPARγ include modified fatty acids, cyclopentenone-containing prostaglandins, triterpenoids, and the thiazolidinediones, a class of insulin-sensitizing drugs used in the treatment of type II diabetes (reviewed in Ref. 13Willson T.M. Brown P.J. Sternbach D.D. Henke B.R. J. Med. Chem. 2000; 43: 527-549Crossref PubMed Scopus (1706) Google Scholar). Anti-tumor properties of PPARγ agonists have been reported. For example, thiazolidinediones have been shown to suppress the growth of human colon and breast cancer cell linesin vitro and in vivo in the mouse (14Sarraf P. Mueller E. D. S.A. S. C. Nat. Med. 1998; PubMed Scopus Google Scholar, E. C. K. D. H. P. D. S. A. 1998; PubMed Scopus Google and a member of a class of PPARγ agonists in a Y. R. T. T.M. 1999; Google Scholar). However, of in a mouse in which of is E. P. R.M. Nat. Med. 1998; PubMed Scopus Google P. J. K. M. R. J. Nat. Med. 1998; PubMed Scopus Google suggesting effects on the of thiazolidinediones for apoptotic effects are E. C. K. D. H. P. D. S. A. 1998; PubMed Scopus Google Scholar). the effects of PPARγ ligands on TRAIL-induced apoptosis in cancers cell findings demonstrate a PPARγ-independent for these in in FLIP protein without concomitant reductions in and sensitization of tumor but not types of normal cells to TRAIL-induced apoptosis. The by these PPARγ ubiquitination and proteasome-dependent degradation of FLIP, thus the existence of an for FLIP expression that be for death apoptosis of and and cells were in with and modified the used for colon and cancer were The TRAIL receptors of this species have been to be in acid to human and these cells have been shown to apoptotic to recombinant of TRAIL as human D. Shahrokh Z. Marsters S. Achilles K. Shih D. Mounho B. Hillan K. Totpal K. DeForge L. Schow P. Hooley J. Sherwood S. Pai R. Leung S. Khan L. Gliniak B. Bussiere J. Smith C.A. Strom S.S. Kelley S. Fox J.A. Thomas D. Ashkenazi A. Nat. Med. 2001; 7: 383-385Crossref PubMed Scopus (636) Google Scholar). cells were and were and and in provided and were and in as Y. T. E. A.E. G. L. K. 1999; Google Scholar, T. L. Y. J. Med. Chem. 2000; 43: PubMed Scopus Google Scholar). recombinant TNF and TRAIL were and The and were and were and or cells were the For cells with were for in and with ligands for the reduce the with to ligand activity with the and with a The activity of by with for and For apoptosis cells in or were with of and of and dominant-negative PPARγ S. D.A. J. 1999; PubMed Scopus Google Scholar, M. M. M. C. J. Biol. Chem. 2000; PubMed Scopus Google Scholar). The of by of For FLIP or cells by a of as H. Google Scholar). were in which the and in the were with the of natural to activity H. J. Biol. Chem. 1999; PubMed Scopus Google Scholar). The to were for protein and with in for of a as R. J. 1997; PubMed Scopus Google Scholar). assays were a the cells were in and for to were with of PPARγ modulators with or without TRAIL for for and a by cells in and with 4,6-diamidino-2-phenylindole the of cells by were prepared cells, and were as Y. J. Biol. Chem. 1998; PubMed Scopus Google Scholar). a were with kinase with the with of for and by in in were to cell prepared with or cytosolic prepared as were to and to with the S. D.A. J. 1999; PubMed Scopus Google or C. J.P. Krammer P.H. Peter M.E. J. Biol. Chem. 1997; PubMed Scopus Google and in for by with for or with were used as were by an For cells were with either or TRAIL or for were with and in of and for of cell were in for for the were with of and of for The were with the and the and were to analysis for and were with PPARγ ligands for and with TNF for prepared as were with of for and of protein were and and more with the kinase assays were in of kinase of and of for The were to were and to cells were with FLIP and cells were with for in the or presence of and in of and by for with of proteins were in and of and by or cells were with the ligands for and and with to the The for by the human with and with of the were by were and to the effects of PPARγ modulators on tumor cell to TRAIL, the effects of of PPARγ ligands as a natural PPARγ and synthetic thiazolidinediones PPARγ and the and which as a and as an of Y. T. T.M. 2000; PubMed Google Scholar). When a variety of tumor cell and of most of these PPARγ modulators on cell as by assays and not For example, of cells were of of treatment with or cytotoxic activity which anti-tumor activity in tumor not The of these tumor cell to TRAIL also When with TRAIL, of the tumor cells of tumor with TRAIL, PPARγ modulators TRAIL by tumor However, treatment of cancer cell with TRAIL and PPARγ modulators in reductions in of for PPARγ modulators and tumor cell the of TRAIL and the of PPARγ modulators the of PPARγ modulators and TRAIL to tumor cell the of TRAIL and PPARγ modulators not cytotoxic to normal cells, including of cells, and and not these were attributed to induction of apoptosis, tumor cell were with TRAIL in with PPARγ and apoptosis by of cells with apoptotic as by and activity in cell on of the and of the poly(ADP-ribose) polymerase that tumor as cancer cancer and cancer are by the of PPARγ modulators and TRAIL to apoptosis and and the these cells with either TRAIL or PPARγ modulators The TRAIL-induced cell death further an apoptotic mechanism. The of TRAIL and PPARγ modulators not to a shift in the of apoptosis as demonstrated by analysis to effects on PPARγ PPARγ modulators have been to the IκB and induction A. P. G. T. Y. M. Nature. 2000; PubMed Scopus Google Scholar). Because in apoptosis induced by expression of apoptosis-suppressing L. S. A. 1997; PubMed Scopus Google Scholar, C. M. R. D. Baldwin A. Science. 1998; 281: PubMed Scopus Google of activity or of induction correlated with the of PPARγ modulators to sensitize tumor cells to TRAIL. For activity tumor cell as were for with PPARγ modulators which demonstrated sensitize tumor cells to TRAIL, including and Because TRAIL not significant TNF to for to were and by activity vitro kinase as an in vitro of of protein by a of with A. P. G. T. Y. M. Nature. 2000; PubMed Scopus Google G., M. M. G. S. A. 2000; PubMed Scopus Google and activity by about the PPARγ modulators and on activity of activity the of and to sensitize tumor cells to TRAIL. were by induction binding of to For example, TNF used as a for inducing binding and or induction and levels of binding activity by about with the kinase PPARγ modulators that sensitize tumor cells to TRAIL reduce activity and induction but not further the of to effects of PPARγ modulators on TRAIL levels of were also in cells with TRAIL of and correlated with induction of apoptosis, of as a for apoptosis to TNF reductions in levels in cells, and this correlated with sensitization to TRAIL-induced apoptosis, as by levels of in cells were not by and may have even been all of these PPARγ modulators cells to TRAIL-induced apoptosis. We also prostaglandins, of which and which effects on with TRAIL-induced the and of and and levels of to induction by either TRAIL or through of activity as A. P. G. T. Y. M. Nature. 2000; PubMed Scopus Google but to sensitize tumor cells to TRAIL-induced apoptosis reductions in not with sensitization of tumor cells to TRAIL. for a that PPARγ modulators and sensitize tumor cells to TRAIL, by the levels of proteins that are to be to mechanisms of TRAIL or TNF including the the TRAIL death receptors, and the TRAIL decoy receptors, and the adapter proteins and the the and FLIP, a protein that binds and and apoptosis induction by TNF family death receptors M. Thome M. Hahne M. Schneider P. Hofmann K. Steiner V. Bodmer J.-L. Schröter M. Burns K. Mattmann C. Rimoldi D. French L.E. Tschopp J. Nature. 1997; 388: 190-195Crossref PubMed Scopus (2231) Google Scholar). the levels of FLIP were by PPARγ modulators PPARγ modulators and that been demonstrated to sensitize tumor cells to TRAIL-induced apoptosis reductions in the levels of including and FLIP protein levels were not in cells with that to sensitize tumor cells to TRAIL, including and a also not reductions in FLIP and not sensitize tumor cells to TRAIL This of FLIP levels by PPARγ modulators in tumor TRAIL sensitization for and are in Furthermore, the of PPARγ modulators to FLIP levels with the to apoptosis and tumor cell expressed the of FLIP the protein in PPARγ modulators the levels of and The FLIP protein and of ligand-activated death receptor T. F. A. Hofmann K. Tschopp J. J. Biol. Chem. 2001; PubMed Scopus Google Scholar, A. S. Krammer P.H. S. J. Biol. Chem. 2001; PubMed Scopus Google Scholar). PPARγ modulators sensitize cells to TRAIL by FLIP to of to TRAIL receptors and this cells were with or without TRAIL and PPARγ and in and the TRAIL receptor and FLIP, and adapter were by of by the but not by When with TRAIL or with However, cells as studies of cells T. F. A. Hofmann K. Tschopp J. J. Biol. Chem. 2001; PubMed Scopus Google Scholar, A. S. Krammer P.H. S. J. Biol. Chem. 2001; PubMed Scopus Google that by recruited to the A. S. Krammer P.H. S. J. Biol. Chem. 2001; PubMed Scopus Google Scholar, C. Krammer P.H. Peter M.E. J. Biol. Chem. 1999; PubMed Scopus Google Scholar). The FLIP protein not in these because of with the for cells with the of and TRAIL in of FLIP and of with a of the receptor of the cells by demonstrated levels of and in cells with the of and TRAIL but not in cells with either of were in cell thus an for of to also by on these of the and of the of the reductions of FLIP protein in tumor cell with PPARγ overexpression of FLIP has on the of PPARγ modulators to sensitize cells to TRAIL. of cells with an expression FLIP the of and to sensitize tumor cells to TRAIL, as by reductions in apoptosis of the that FLIP protein levels were in the cells which the FLIP expression evidence that the sensitization of tumor cells to TRAIL by PPARγ modulators be to in FLIP of FLIP also apoptosis with S. E. 2000; Google Scholar, H. J. Biol. Chem. 2000; PubMed Scopus Google Scholar, T. R.C. Thome M. F. M. Burns K. Hahne M. M. Tschopp J. Curr. 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PubMed Scopus Google apoptosis induced by the of TRAIL and PPARγ modulators as overexpression of not suppress apoptosis with evidence that TRAIL and death receptors apoptosis through mechanisms in many types of FLIP were used to of FLIP protein levels is to sensitize tumor cells to TRAIL. of cells with FLIP in a in the levels of the and of FLIP with cells This in FLIP protein levels correlated with of cells to TRAIL-induced apoptosis that FLIP expression is to sensitize tumor cell to TRAIL-induced apoptosis. the used here are to a PPARγ-independent for to sensitize tumor cells to TRAIL, that PPARγ agonists and agonists and antagonists were We the effects of PPARγ on TRAIL-induced apoptosis, that PPARγ modulators were through a be more PPARγ levels are cells were for these studies because of levels of PPARγ protein G., M. M. G. S. A. 2000; PubMed Scopus Google Scholar). PPARγ on apoptosis induction by the of TRAIL and of of cells as by a green fluorescent protein that these in levels of PPARγ assays were in that of cells with in in ligand-activated expression of a PPAR-response elements We that and are capable of to sensitize tumor cells to TRAIL not with effects on an a of PPARγ that as a dominant-negative of the protein M. M. M. C. J. Biol. Chem. 2000; PubMed Scopus Google Scholar). of dominant-negative PPARγ to sensitization of cells to TRAIL to induction of PPARγ activity by assays a We that the effects of be effects on assays were to levels of in and cells with PPARγ a in FLIP protein levels were not in levels or in levels of that as controls and not PPARγ modulators to FLIP protein reductions through a further for a PPARγ-independent mechanism. of the of FLIP protein reductions in cells with and PPARγ modulators a with and of FLIP protein cells by cells that induced in the of FLIP protein degradation the of in the of FLIP protein induced by PPARγ tumor cells were with of the and and and and FLIP by suggesting a for the in this mechanism. of and Because the PPARγ modulators ubiquitination of the FLIP of with demonstrated the presence of of FLIP treatment with The of these of FLIP with the and levels to This to FLIP, on cells were and the were by cells with the as also induced a in FLIP, of a of FLIP but the of of FLIP to FLIP, the of ubiquitination and levels of and to be regulated by P. 2001; PubMed Scopus Google B. D. Nature. 2000; PubMed Scopus Google were not by treatment of cells further evidence of ubiquitination of FLIP, cells were with FLIP and cells for with or the of these were to to by FLIP in cells with either or but not in cells Furthermore, the of and to even in FLIP with the that induces in FLIP degradation of the FLIP these suggest that ubiquitination of FLIP, thus the degradation of FLIP protein by the this the existence of an that ubiquitination and degradation of the FLIP protein and is capable of types of the cells to death apoptosis in receptor of has also been to levels of FLIP protein without concomitant in levels A. T.S. Lynch D.H. J. Immunol. 1999; Google Scholar). reductions in FLIP protein levels induced by are by T. T. F. F. Y. T. Y. S. J.A. Tschopp J. 2001; PubMed Scopus Google Scholar). for of FLIP For many proteins levels are regulated by ubiquitination and proteasome-dependent ubiquitination is induced upon binding of to the target protein (reviewed in Ref. A. J. 1998; PubMed Scopus Google Scholar). this FLIP has been shown to with which a to possess ligase activity T. F. A. Hofmann K. Tschopp J. J. Biol. Chem. 2001; PubMed Scopus Google Scholar). is that PPARγ drugs the expression of or types of mechanisms also be R. A. B. Y. Immunol. 2000; PubMed Scopus Google demonstrated that sensitize human tumor cell to the not We this to tumor cell and to of PPARγ that for to and the of PPARγ have an PPARγ-independent to reduce FLIP protein levels and sensitize cancer cells to apoptosis induction by TRAIL. The evidence a for these the of PPARγ agonists and and antagonists Y. T. T.M. 2000; PubMed Google of PPARγ overexpression and dominant-negative PPARγ to effects of on TRAIL-induced and in FLIP protein levels without concomitant reductions in suggesting a of studies of effects of thiazolidinediones and cells PPARγ mice have demonstrated PPARγ-independent of by A. Y. L. D. P. R.M. Nat. Med. 2001; 7: PubMed Scopus Google suggesting an target of these has been that the effects of thiazolidinediones on cells in vitro vivo are of this on cells S.S. H. R.M. J.A. 2001; Google Scholar). this the IκB that activity have been identified as of and types of PPARγ However, and also are not the of the because overexpression of to TRAIL resistance and because not or reduce binding We that natural PPARγ agonists and and synthetic PPARγ including thiazolidinediones and and and with an in reductions in FLIP protein inducing FLIP protein degradation through a PPARγ modulators with a novel target be used for of these that the to reduce FLIP levels without PPARγ or of this type for the target that controls FLIP that as are more the thiazolidinediones here inducing FLIP degradation and tumor cells to TRAIL, this class of be in the to agonists of the FLIP degradation that lack effects on used has been to apoptosis of and cell through a of but not and through a mechanisms that is by but not by Y. P. A. T. S. D. 2000; Google Scholar, Y. P. R. S. D. 2001; PubMed Scopus Google Scholar). are with of the apoptosis which is by TNF family death receptors, as to the apoptosis a (reviewed in Ref. J. 2000; PubMed Google Scholar). and may possess the to the as without of TRAIL or death provided are to be these expression of TNF family death ligands or receptors, thus for these findings that and possess induction of FLIP which of the because FLIP has been to and kinase T. F. A. Hofmann K. Tschopp J. J. Biol. Chem. 2001; PubMed Scopus Google to is also that FLIP expression apoptosis in a cell has been that of recombinant TRAIL apoptosis of normal human thus raising about (reviewed in Ref. S. Nat. Med. 2000; PubMed Scopus Google Scholar). demonstrated that toxicity to is with TRAIL and is not with trimeric TRAIL D. Shahrokh Z. Marsters S. Achilles K. Shih D. Mounho B. Hillan K. Totpal K. DeForge L. Schow P. Hooley J. Sherwood S. Pai R. Leung S. Khan L. Gliniak B. Bussiere J. Smith C.A. Strom S.S. Kelley S. Fox J.A. Thomas D. Ashkenazi A. Nat. Med. 2001; 7: 383-385Crossref PubMed Scopus (636) Google Scholar). were to of human to the effects of treatment with TRAIL and PPARγ an but to induction of apoptosis. this the TRAIL receptors of are to human D. Shahrokh Z. Marsters S. Achilles K. Shih D. Mounho B. Hillan K. Totpal K. DeForge L. Schow P. Hooley J. Sherwood S. Pai R. Leung S. Khan L. Gliniak B. Bussiere J. Smith C.A. Strom S.S. Kelley S. Fox J.A. Thomas D. Ashkenazi A. Nat. Med. 2001; 7: 383-385Crossref PubMed Scopus (636) Google Scholar). has been demonstrated that these human TRAIL with D. Shahrokh Z. Marsters S. Achilles K. Shih D. Mounho B. Hillan K. Totpal K. DeForge L. Schow P. Hooley J. Sherwood S. Pai R. Leung S. Khan L. Gliniak B. Bussiere J. Smith C.A. Strom S.S. Kelley S. Fox J.A. Thomas D. Ashkenazi A. Nat. Med. 2001; 7: 383-385Crossref PubMed Scopus (636) Google Scholar). these and human are in apoptotic to and of TRAIL, trimeric TRAIL to apoptosis of human and cells, TRAIL kills species D. Shahrokh Z. Marsters S. Achilles K. Shih D. Mounho B. Hillan K. Totpal K. DeForge L. Schow P. Hooley J. Sherwood S. Pai R. Leung S. Khan L. Gliniak B. Bussiere J. Smith C.A. Strom S.S. Kelley S. Fox J.A. Thomas D. Ashkenazi A. Nat. Med. 2001; 7: 383-385Crossref PubMed Scopus (636) Google Scholar). are a for human TRAIL-induced apoptosis is The effects on normal malignant cells of treatment with TRAIL PPARγ modulators in vitro suggest that be to these for the treatment of because class PPARγ modulators are in as for treatment of type II in vivo are that these or PPARγ modulators be used for an as of cancer cells to TRAIL and of TNF family death We M. R. D. and R. R. for and S. and S. for F. and W. of for and R. for We also and for the TRAIL and TRAIL receptor of cancer cell