Key points are not available for this paper at this time.
The dioxin (aryl hydrocarbon) receptor is a ligand-dependent transcription factor that induces expression of a number of genes encoding drug metabolizing enzymes. In the absence of ligand the dioxin receptor is present in the cytoplasmic compartment of the cell associated with the molecular chaperone hsp90, which has been implicated in regulating the correct folding of the ligand binding domain of the receptor. In this study we have examined a potential role of the hsp90-associated p23 protein in the activation process of the dioxin receptor to a DNA binding form. In an in vitro model we show that addition of ligand alone to the dioxin receptor fails to induce release of hsp90 from the dioxin receptor. In the presence of ligand, this release was, however, induced upon addition of purified preparations of Arnt. Interestingly, p23 was also found to be associated with the nonactivated form of the dioxin receptor. Following fractionation on sucrose gradients p23 was dissociated from the receptor-hsp90 complex generating a receptor form, which showed ligand-independent release of hsp90 by Arnt and, consequently, ligand-independent activation of the DNA binding activity of the dioxin receptor. Ligand dependence was reconstituted in the presence of molybdate, a transition metal ion known to stabilize the interaction between the molecular chaperone hsp90 and p23. Taken together these experiments suggest a role of p23 in modulating ligand responsiveness in the activation process of the dioxin receptor. The dioxin (aryl hydrocarbon) receptor is a ligand-dependent transcription factor that induces expression of a number of genes encoding drug metabolizing enzymes. In the absence of ligand the dioxin receptor is present in the cytoplasmic compartment of the cell associated with the molecular chaperone hsp90, which has been implicated in regulating the correct folding of the ligand binding domain of the receptor. In this study we have examined a potential role of the hsp90-associated p23 protein in the activation process of the dioxin receptor to a DNA binding form. In an in vitro model we show that addition of ligand alone to the dioxin receptor fails to induce release of hsp90 from the dioxin receptor. In the presence of ligand, this release was, however, induced upon addition of purified preparations of Arnt. Interestingly, p23 was also found to be associated with the nonactivated form of the dioxin receptor. Following fractionation on sucrose gradients p23 was dissociated from the receptor-hsp90 complex generating a receptor form, which showed ligand-independent release of hsp90 by Arnt and, consequently, ligand-independent activation of the DNA binding activity of the dioxin receptor. Ligand dependence was reconstituted in the presence of molybdate, a transition metal ion known to stabilize the interaction between the molecular chaperone hsp90 and p23. Taken together these experiments suggest a role of p23 in modulating ligand responsiveness in the activation process of the dioxin receptor. The bHLH-PAS dioxin (aryl hydrocarbon) 1The abbreviation used is: dioxin, TCDD, 2,3,7,8-tetrachlorodibenzo-p-dioxin; hsp, heat shock protein; XRE, xenobiotic response element; EMSA, electrophoretic mobility shift assay.1The abbreviation used is: dioxin, TCDD, 2,3,7,8-tetrachlorodibenzo-p-dioxin; hsp, heat shock protein; XRE, xenobiotic response element; EMSA, electrophoretic mobility shift assay. receptor (1Ema M. Sogawa K. Watanabe N. Chujoh Y. Matsushita N. Gotoh O. Funae Y. Fujii-Kuriyama K.Y. Biochem. Biophys. Res. Commun. 1992; 184: 246-253Crossref PubMed Scopus (351) Google Scholar, 2Burbach K.M. Poland A. Bradfield C.A. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 8185-8189Crossref PubMed Scopus (715) Google Scholar) is a member of a growing family of transcription factors that includes, among others, a number of circadian rhythmicity regulatory proteins (3Dunlap J.C. Cell. 1999; 96: 271-290Abstract Full Text Full Text PDF PubMed Scopus (2341) Google Scholar,4Sassone-Corsi P. Nature. 1998; 392: 871-874Crossref PubMed Scopus (81) Google Scholar) and proteins such as the hypoxia-inducible factor HIF-1α (5Wang G.L. Jiang B.H. Rue E.A. Semenza G.L. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 5510-5514Crossref PubMed Scopus (4995) Google Scholar), its endothelial cell-specific homologue E-PAS/HLF (6Tian H. McKnight S.L. Russell D.W. Genes Dev. 1997; 11: 72-82Crossref PubMed Scopus (1060) Google Scholar, 7Ema M. Taya S. Yokotani N. Sogawa K. Matsuda Y. Fujii-Kuriyama Y. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 4273-4278Crossref PubMed Scopus (837) Google Scholar), and Arnt (8Hoffman E.C. Reyes H. Chu F.F. Sander F. Conley L.H. Brooks B.A. Hankinson O. Science. 1991; 252: 954-958Crossref PubMed Scopus (836) Google Scholar), which is a partner factor both of the dioxin receptor and of hypoxia-inducible factors. These factors, with the possible exception of Arnt, appear to be conditionally regulated and respond to different stimuli. The dioxin receptor is activated by dioxin (9Poellinger L. Whitelaw M. Pongratz I. Wilhelmsson A. Gradin K. Berghard A. Bernard B.A. Shroot B. From Molecular Biology to Therapeutics. 5. Karger, Basel, Switzerland1993Google Scholar) and related environmental pollutants, whereas HIF 1α is activated under conditions of oxygen deprivation to induce the expression of genes encoding, e.g. erythropoietin and vascular endothelial growth factor (10Wang G.L. Semenza G.L. Curr. Opin. Hematol. 1996; 3: 156-162Crossref PubMed Scopus (105) Google Scholar). In the absence of ligand the dioxin receptor is present in a latent conformation in the cytoplasmic compartment of the cell (11Ikuta T. Eguchi H. Tachibana T. Yoneda Y. Kawajiri K. J. Biol. Chem. 1998; 273: 2895-2904Abstract Full Text Full Text PDF PubMed Scopus (209) Google Scholar) associated with the molecular chaperone hsp90 (12Wilhelmsson A. Cuthill S. Denis M. Wikstrom A.C. Gustafsson J.A. Poellinger L. EMBO J. 1990; 9: 69-76Crossref PubMed Scopus (172) Google Scholar). Hsp90 is required both for maintaining the dioxin receptor in a latent non-DNA binding state and a ligand binding conformation (13Pongratz I. Mason G.F. Poellinger L. J. Biol. Chem. 1992; 267: 13728-13734Abstract Full Text PDF PubMed Google Scholar). Expression of the dioxin receptor in mutant yeast cells containing reduced levels of hsp90 abolishes ligand responsiveness demonstrating the critical importance of hsp90 for dioxin receptor function (14Carver L.A. Jackiw V. Bradfield C.A. J. Biol. Chem. 1994; 269: 30109-30112Abstract Full Text PDF PubMed Google Scholar, 15Whitelaw M.L. McGuire J. Picard D. Gustafsson J.A. Poellinger L. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 4437-4441Crossref PubMed Scopus (111) Google Scholar). The nuclear form of the dioxin receptor interacts with Arnt (16Reyes H. Reisz-Porszasz S. Hankinson O. Science. 1992; 256: 1193-1195Crossref PubMed Scopus (684) Google Scholar, 17Whitelaw M. Pongratz I. Wilhelmsson A. Gustafsson J.Å. Poellinger L. Mol. Cell. Biol. 1993; 13: 2504-2514Crossref PubMed Scopus (183) Google Scholar, 18Probst M.R. Reisz-Porszasz S. Agbunag R.V. Ong M.S. Hankinson O. Mol. Pharmacol. 1993; 44: 511-518PubMed Google Scholar) and does no longer posses the ability to bind ligand and does not interact with the molecular chaperone hsp90 (12Wilhelmsson A. Cuthill S. Denis M. Wikstrom A.C. Gustafsson J.A. Poellinger L. EMBO J. 1990; 9: 69-76Crossref PubMed Scopus (172) Google Scholar, 13Pongratz I. Mason G.F. Poellinger L. J. Biol. Chem. 1992; 267: 13728-13734Abstract Full Text PDF PubMed Google Scholar). This form of the receptor specifically binds to enhancer elements known as XREs (xenobiotic response elements) of a number of genes encoding drug-metabolizing enzymes (17Whitelaw M. Pongratz I. Wilhelmsson A. Gustafsson J.Å. Poellinger L. Mol. Cell. Biol. 1993; 13: 2504-2514Crossref PubMed Scopus (183) Google Scholar, 18Probst M.R. Reisz-Porszasz S. Agbunag R.V. Ong M.S. Hankinson O. Mol. Pharmacol. 1993; 44: 511-518PubMed Google Scholar). Release of hsp90 from the latent form of the dioxin receptor is therefore a critical step in the activation process of the dioxin receptor. Recently the hepatitis virus X protein-associated protein (XAP-2) also known as ARA 9 or AIP of 38 kDa has been shown to interact with the latent form of the dioxin receptor (19Meyer B.K. Pray-Grant M.G. Van den Heuvel J.P. Perdew G.H. Mol. Cell. Biol. 1998; 18: 978-988Crossref PubMed Scopus (305) Google Scholar, 20Carver L.A. Bradfield C.A. J. Biol. Chem. 1997; 272: 11452-11456Abstract Full Text Full Text PDF PubMed Scopus (346) Google Scholar, 21Ma Q. Whitlock Jr., J.P. J. Biol. Chem. 1997; 272: 8878-8884Abstract Full Text Full Text PDF PubMed Scopus (361) Google Scholar). This protein has been reported to increase the transcriptional activity of the dioxin receptor, although the mechanism of action has not been elucidated (22Carver L.A. LaPres J.J. Jain S. Dunham E.E. Bradfield C.A. J. Biol. Chem. 1998; 273: 33580-33587Abstract Full Text Full Text PDF PubMed Scopus (174) Google Scholar). The co-chaperone protein p23 (23Johnson J.L. Beito T.G. Krco C.J. Toft D.O. Mol. Cell. Biol. 1994; 14: 1956-1963Crossref PubMed Scopus (179) Google Scholar) has been shown to be associated with the N-terminal ATP binding domain of hsp90 (24Grenert J.P. Sullivan W.P. Fadden P. Haystead T.A.J. Clark J. Mimnaugh E. Krutzsch H. Ochel H.-J. Schulte T.W. Sausville E. Neckers L.M. Toft D.O. J. Biol. Chem. 1997; 272: 23843-23850Abstract Full Text Full Text PDF PubMed Scopus (507) Google Scholar). p23 has also been found to be associated with non-activated form of selected members of the steroid receptor superfamily such as the glucocorticoid and progesterone receptors (25Pratt W.B. Toft D.O. Endocr. Rev. 1997; 18: 306-360Crossref PubMed Scopus (1529) Google Scholar). Moreover, p23 has been reported recently to be associated with the dioxin receptor (26Nair S.C. Toran E.J. Rimerman R.A. Hjermstad S. Smithgall T.E. Smith D.F. Cell Stress Chaperones. 1996; 1: 237-250Crossref PubMed Scopus (197) Google Scholar). The role of p23 in modulating target protein function is, however, not clear. Given the background that interaction with p23 correlates with high affinity ligand binding activity of certain steroid receptors (27Dittmar K.D. Demady D.R. Stancato L.F. Krishna P. Pratt W.B. J. Biol. Chem. 1997; 272: 21213-21220Abstract Full Text Full Text PDF PubMed Scopus (234) Google Scholar), it seems plausible that p23 is involved regulation and stabilization of the ligand binding conformation of these receptors. In addition to hsp90 and p23, other protein factors are involved in the formation of the high affinity ligand binding steroid receptor form. In fact, formation of such a complex appears to involve p60 (28Smith D.F. Sullivan W.P. Marion T.N. Zaitsu K. Madden B. McCormick D.J. Toft D.O. Mol. Cell. Biol. 1993; 13: 869-876Crossref PubMed Scopus (247) Google Scholar), also known as HOP (Hsp organizing Protein), several immunophilins, and possibly factors that are found in association with proteins such as hsp70 (25Pratt W.B. Toft D.O. Endocr. Rev. 1997; 18: 306-360Crossref PubMed Scopus (1529) Google Scholar). We have observed previously that ligand-dependent release of hsp90 in vitro requires the interaction of the dioxin receptor with additional cellular factors, including Arnt (29McGuire J. Whitelaw M.L. Pongratz I. Gustafsson J.Å. Poellinger L. Mol. Cell. Biol. 1994; 14: 2438-2446Crossref PubMed Scopus (116) Google Scholar). Interestingly, in the present study, fractionation of cellular extracts through sucrose density gradients yielded an hsp90-associated form of the dioxin receptor, which did not require ligand to generate the DNA binding complex with Arnt. This loss of ligand dependence correlated with of p23 from the dioxin receptor-hsp90 was possible to ligand dependence in receptor activation by addition of molybdate, an that has been shown stabilize the interaction between hsp90 and p23. these a role of p23 in modulating ligand responsiveness in receptor The of and has been previously (17Whitelaw M. Pongratz I. Wilhelmsson A. Gustafsson J.Å. Poellinger L. Mol. Cell. Biol. 1993; 13: 2504-2514Crossref PubMed Scopus (183) Google Scholar, I. Whitelaw M.L. Poellinger L. Mol. Cell. Biol. 1998; 18: PubMed Scopus Google Scholar). In vitro of the dioxin receptor and Arnt was to the in expression of Arnt has been in I. Whitelaw M.L. Poellinger L. Mol. Cell. Biol. 1998; 18: PubMed Scopus Google Scholar). cells and the mutant in as previously (12Wilhelmsson A. Cuthill S. Denis M. Wikstrom A.C. Gustafsson J.A. Poellinger L. EMBO J. 1990; 9: 69-76Crossref PubMed Scopus (172) Google Scholar). to in an of extracts by cells and in and in and the the cells in of and for The was as the and used or in extracts of of or in vitro dioxin receptor was on sucrose gradients in containing and as The gradients to a of in a by from the of the and used as The dioxin receptor was by of or for with or DNA binding by a mobility shift as J. Cuthill S. Denis M. Poellinger L. Gustafsson J.Å. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). DNA binding with the protein in and to a of The of the DNA binding between and S. Wilhelmsson A. Poellinger L. Mol. Cell. Biol. 1991; 11: PubMed Scopus Google Scholar) a of the was to the as in the presence of of The for and on of and a J. Cuthill S. Denis M. Poellinger L. Gustafsson J.Å. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). In DNA binding the dioxin receptor (17Whitelaw M. Pongratz I. Wilhelmsson A. Gustafsson J.Å. Poellinger L. Mol. Cell. Biol. 1993; 13: 2504-2514Crossref PubMed Scopus (183) Google Scholar, K. Wilhelmsson A. Poellinger L. Berghard A. J. Biol. Chem. 1993; Full Text PDF PubMed Google Scholar) or Arnt Whitelaw M.L. McGuire J. Wilhelmsson A. Poellinger L. Gustafsson J.Å. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar), or to the binding together with protein and the to the of In dioxin receptor or Arnt with (23Johnson J.L. Beito T.G. Krco C.J. Toft D.O. Mol. Cell. Biol. 1994; 14: 1956-1963Crossref PubMed Scopus (179) Google Scholar), or receptor of protein in in or receptor experiments or in experiments was and under for was in and proteins by addition of of the dioxin receptor on sucrose density gradients a to different of the receptor. the dioxin receptor be both in the 9 of the to an molecular of kDa or in the with an of kDa (12Wilhelmsson A. Cuthill S. Denis M. Wikstrom A.C. Gustafsson J.A. Poellinger L. EMBO J. 1990; 9: 69-76Crossref PubMed Scopus (172) Google Scholar, 13Pongratz I. Mason G.F. Poellinger L. J. Biol. Chem. 1992; 267: 13728-13734Abstract Full Text PDF PubMed Google Scholar, T. Mason Wilhelmsson A. Cuthill S. J. Gustafsson J.Å. Poellinger L. J. Biol. Chem. 1990; Full Text PDF PubMed Google Scholar). These different of the dioxin the 9 form the ligand receptor whereas the form the DNA binding complex between the receptor and Arnt (12Wilhelmsson A. Cuthill S. Denis M. Wikstrom A.C. Gustafsson J.A. Poellinger L. EMBO J. 1990; 9: 69-76Crossref PubMed Scopus (172) Google Scholar, 17Whitelaw M. Pongratz I. Wilhelmsson A. Gustafsson J.Å. Poellinger L. Mol. Cell. Biol. 1993; 13: 2504-2514Crossref PubMed Scopus (183) Google Scholar). In the present experiments we have used extracts from D.W. Hankinson O. J. Biol. Chem. Full Text PDF PubMed Google Scholar) cells a mutant form of Arnt K. A. Sogawa K. Fujii-Kuriyama Y. J. Biochem. 1997; PubMed Scopus Google Scholar) that does not the dioxin receptor to bind DNA (8Hoffman E.C. Reyes H. Chu F.F. Sander F. Conley L.H. Brooks B.A. Hankinson O. Science. 1991; 252: 954-958Crossref PubMed Scopus (836) Google Scholar). of Arnt to this the DNA binding activity of the receptor in H. Reisz-Porszasz S. Hankinson O. Science. 1992; 256: 1193-1195Crossref PubMed Scopus (684) Google Scholar, 17Whitelaw M. Pongratz I. Wilhelmsson A. Gustafsson J.Å. Poellinger L. Mol. Cell. Biol. 1993; 13: 2504-2514Crossref PubMed Scopus (183) Google Scholar). The was with for and on a sucrose density The with Arnt for and binding activity was by The of the that binding activity in the of the to the of the receptor-hsp90 complex (12Wilhelmsson A. Cuthill S. Denis M. Wikstrom A.C. Gustafsson J.A. Poellinger L. EMBO J. 1990; 9: 69-76Crossref PubMed Scopus (172) Google Scholar). with the model that ligand alone is not to induce release of hsp90 requires Arnt (29McGuire J. Whitelaw M.L. Pongratz I. Gustafsson J.Å. Poellinger L. Mol. Cell. Biol. 1994; 14: 2438-2446Crossref PubMed Scopus (116) Google Scholar), ligand did not induce in the of the dioxin receptor from 9 to the of the to the of receptor (13Pongratz I. Mason G.F. Poellinger L. J. Biol. Chem. 1992; 267: 13728-13734Abstract Full Text PDF PubMed Google Scholar). the role of ligand in the receptor to an binding form, we extracts on sucrose gradients and the in the 9 of the This was with dioxin or alone for in the presence of and binding activity was by Interestingly, an binding complex was both in the presence or absence of ligand and This complex both the dioxin receptor and Arnt, as by not In the dioxin receptor in extracts requires ligand to interact with in vitro M.L. M. Gustafsson J.Å. Poellinger L. EMBO J. 1993; PubMed Scopus Google Scholar) or not Arnt to generate the binding these suggest that the ligand-dependent mechanism of receptor activation been upon fractionation of the receptor. Given the loss of ligand dependence to induce DNA binding activity by the dioxin receptor, we examined the of Arnt on ligand binding activity by sucrose receptor in we in vitro dioxin receptor on a sucrose and the dioxin in the 9 of the The to sucrose and in the presence or absence of Arnt for This was with for and on a sucrose density Following the for shown in the dioxin receptor was to bind upon addition of Arnt, ligand binding activity was In of these we also examined the of Arnt to induce release of hsp90 from in vitro dioxin receptor upon fractionation on sucrose with the receptor (29McGuire J. Whitelaw M.L. Pongratz I. Gustafsson J.Å. Poellinger L. Mol. Cell. Biol. 1994; 14: 2438-2446Crossref PubMed Scopus (116) Google Scholar), we observed no release of hsp90 from the 9 dioxin receptor upon of the 9 receptor with ligand alone in the absence of Arnt and Interestingly, however, addition of Arnt to the 9 dioxin receptor form induced of hsp90 from the receptor both in the presence or absence of dioxin with the observed in ligand binding activity The experiments suggest that the latent form of the dioxin receptor upon fractionation on sucrose in ligand-independent release of hsp90 and receptor activation by Arnt. has been that hsp90 binds additional co-chaperone which are for of certain hsp90 associated such as a number of steroid receptors (25Pratt W.B. Toft D.O. Endocr. Rev. 1997; 18: 306-360Crossref PubMed Scopus (1529) Google Scholar). We therefore the potential of hsp90-associated factors in stabilization of the dioxin receptor-hsp90 this we in vitro the dioxin receptor in the presence of and experiments with p23 The dioxin receptor was by p23 whereas in experiments Arnt, which does not interact with hsp90, to interact with p23 and We the role of ligand and Arnt on release of p23 from the dioxin receptor In vitro receptor was in the absence or presence of dioxin, Arnt, or both Interestingly, addition of Arnt or ligand alone did not induce release of p23 from the dioxin receptor complex in the presence of a of Arnt and ligand we observed of p23 from the dioxin receptor and In of the background that p23 has been shown to stabilize binding between hsp90 and other target proteins (27Dittmar K.D. Demady D.R. Stancato L.F. Krishna P. Pratt W.B. J. Biol. Chem. 1997; 272: 21213-21220Abstract Full Text Full Text PDF PubMed Scopus (234) Google Scholar), we sucrose the interaction of p23 with the 9 dioxin receptor form. In vitro dioxin receptor was on a sucrose density and in the 9 and used in p23 experiments with in vitro dioxin receptor showed of the receptor p23 a in of dioxin receptor by with p23 was and In dioxin receptor of dioxin receptor from the or the 9 and In these experiments that the association of the dioxin receptor-hsp90 complex with p23 upon with the loss of of ligand to induce binding and other transition metal have been shown to stabilize the interaction between hsp90 and a number of hsp90 different members of the steroid receptor family (27Dittmar K.D. Demady D.R. Stancato L.F. Krishna P. Pratt W.B. J. Biol. Chem. 1997; 272: 21213-21220Abstract Full Text Full Text PDF PubMed Scopus (234) Google Scholar). We therefore extracts from cells with to fractionation through sucrose density gradients containing the dioxin receptor was as a 9 This was with Arnt both in the presence or absence of dioxin and of the binding activity of the dioxin complex was by to Arnt the dioxin complex did not require ligand to bind the target fractionation of the receptor in a sucrose density and however, addition of to the formation of the DNA binding complex ligand-dependent and The process of activation of the dioxin receptor from a cytoplasmic latent form to a nuclear form release of hsp90 (12Wilhelmsson A. Cuthill S. Denis M. Wikstrom A.C. Gustafsson J.A. Poellinger L. EMBO J. 1990; 9: 69-76Crossref PubMed Scopus (172) Google Scholar, 13Pongratz I. Mason G.F. Poellinger L. J. Biol. Chem. 1992; 267: 13728-13734Abstract Full Text PDF PubMed Google Scholar). We have shown previously in addition to ligand, Arnt of the dioxin receptor-hsp90 complex (29McGuire J. Whitelaw M.L. Pongratz I. Gustafsson J.Å. Poellinger L. Mol. Cell. Biol. 1994; 14: 2438-2446Crossref PubMed Scopus (116) Google Scholar). In to M.R. Reisz-Porszasz S. Hankinson O. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar) have observed release of hsp90 from the dioxin receptor in the absence of Arnt upon addition of dioxin in The these in is different of the in the used by M.R. Reisz-Porszasz S. Hankinson O. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). is known to steroid receptor-hsp90 (25Pratt W.B. Toft D.O. Endocr. Rev. 1997; 18: 306-360Crossref PubMed Scopus (1529) Google Scholar). In the present study of extracts from cells a mutant form of Arnt with dioxin to fractionation through a sucrose density yielded of dioxin receptor the of the receptor-hsp90 of a to induce a release of hsp90 under these it hsp90 is from the receptor or to nuclear the receptor has been observed to be associated with hsp90 upon from purified (12Wilhelmsson A. Cuthill S. Denis M. Wikstrom A.C. Gustafsson J.A. Poellinger L. EMBO J. 1990; 9: 69-76Crossref PubMed Scopus (172) Google Scholar). Moreover, the receptor ligand-dependent nuclear in cells C.A. Poland A. Mol. Pharmacol. 1994; Google Scholar) we to release of Taken these that the receptor be the in association with it be to this of the dioxin receptor through a sucrose density in a loss of the of ligand to generate an binding receptor form, whereas the interaction between hsp90 and the dioxin receptor was not by this Moreover, with the in activation of DNA binding addition of Arnt to the sucrose containing the receptor-hsp90 complex in release of hsp90 in the absence of We these to that involved in stabilization of the latent form of the receptor have been dissociated sucrose In an to such a factor we have examined the role of p23 in dioxin receptor p23 is a protein that has been found to be associated with hsp90 (24Grenert J.P. Sullivan W.P. Fadden P. Haystead T.A.J. Clark J. Mimnaugh E. Krutzsch H. Ochel H.-J. Schulte T.W. Sausville E. Neckers L.M. Toft D.O. J. Biol. Chem. 1997; 272: 23843-23850Abstract Full Text Full Text PDF PubMed Scopus (507) Google Scholar, J.L. Toft D.O. Mol. 1995; 9: PubMed Scopus Google Scholar, Stancato L.F. J.L. Krishna P. Toft D.O. Pratt W.B. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). In the of the progesterone receptor and the glucocorticoid p23 has been found to be associated with the high affinity ligand binding of these receptors (23Johnson J.L. Beito T.G. Krco C.J. Toft D.O. Mol. Cell. Biol. 1994; 14: 1956-1963Crossref PubMed Scopus (179) Google Scholar). has been shown that formation of the ligand binding of these receptors a process a number of different protein are p23, hsp90, and (25Pratt W.B. Toft D.O. Endocr. Rev. 1997; 18: 306-360Crossref PubMed Scopus (1529) Google Scholar, W.B. J. Biol. Chem. 1993; Full Text PDF PubMed Google Scholar, W.B. Cell Biol. 1994; PubMed Scopus Google Scholar). we that p23 is associated with the ligand binding form of the dioxin receptor. Moreover, as in the model in p23 was not upon of the ligand binding domain of the receptor by ligand together with hsp90 associated with the receptor in an complex to of the receptor with Arnt and release of certain steroid receptors show ligand binding affinity in the absence of p23 (27Dittmar K.D. Demady D.R. Stancato L.F. Krishna P. Pratt W.B. J. Biol. Chem. 1997; 272: 21213-21220Abstract Full Text Full Text PDF PubMed Scopus (234) Google Scholar), of p23 from the dioxin receptor by fractionation of the receptor on sucrose gradients did not appear to its ligand binding however, in the absence of p23, release of hsp90 by Arnt and the formation of an binding form did not require is therefore possible that the role of ligand be to the function of p23 by binding to the dioxin receptor and possibly a that the receptor to with Arnt and release This is by the of ligand-dependent binding activity of the dioxin receptor by addition of is a used that the interaction between for the glucocorticoid receptor and hsp90 J.L. Toft D.O. Mol. 1995; 9: PubMed Scopus Google Scholar). In the of factors that in extracts stabilize the interaction between the dioxin receptor and the function of factors. The of these the interaction between p23 and hsp90 is it be a possibly a or a different of such as the glucocorticoid receptor factor Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, J. Biol. Chem. Full Text PDF PubMed Google Scholar, Mol. Cell. 1990; PubMed Scopus Google Scholar). the role of ligand in dioxin receptor activation and the possible of factors in this process to be in the model in a factor is p23, the role of which be to stabilize an complex that the In we that the role of ligand in dioxin receptor activation be to the of hsp90 associated factors such as the co-chaperone p23 and release of hsp90 by Arnt, in of the DNA binding form. We Toft for p23
Kazlauskas et al. (Sat,) studied this question.