[Dioxin-l] Reply to Jon
Henshel, Diane S.
dhenshel@indiana.edu
Wed, 16 Feb 2000 01:44:08 -0500
My favorite paper for destroying the threshold theory is George Lucier's
paper using PCR- enhanced analysis of expression of P450 mRNA. I recall (I
think) that the paper was EHP (Env Health Perspec) but I don't recal the
year, maybe 3 - 5 years ago at a guess.
> -----Original Message-----
> From: Oram, Louise [SMTP:lbo7@cdc.gov]
> Sent: Monday, February 14, 2000 3:01 PM
> To: 'Jon Campbell'
> Cc: dioxin-l@venice.essential.org
> Subject: [Dioxin-l] Reply to Jon
>
>
> Jon
> Thanks so much to Louise for guiding us in this endeavor, even though she
> and Dr. David Bell (who were apparently colleagues in the UK) did so quite
> inadvertently. This short paper makes clear the molecular nature of the Ah
> Receptor site.
>
> >This is a useful link. But as you will probably find from reading it,
> Mark
> tends to generalise and over-simplify, for the general reader. His papers
> are a little more hardcore, some of the chemistry goes straight over my
> head. And as for you finding this page inadvertently. You could have asked
> if I had a web page, or any useful links. (my web page isn't really that
> useful, as I never finished it) I've never hidden who I was and who I work
> for. And I wasn't that hard to find, was I?
>
> Notice the names in the reference list of Denison's (below) mechanism of
> action; Okay, Hankinson, Brad field, Safe. And make the connection to the
> references I recommended you read.
>
>
> Note that as I had originally hypothesized, a single molecule of TCDD
> can bind to the Ah receptor and the bound complex is then transmitted to
> nuclear DNA where it begins to disrupt the normal functioning of the cell.
> My original sources of the hypothesis were popularized versions of the
> analysis below.
>
>
> >Jon, to be correct. Your theory was peppered with such poor
> understanding
> of basic cell biology that it was, when taken as a whole, nonsense. To say
> you have found validation for some small part (?) is a bizarre assumption.
> And I corrected you because you were way off base. The issues I have been
> addressing with you are; not whether dioxin binds, if it didn't bind we
> wouldn't be exchanging any emails, or if in fact that it has a downstream
> effect. The issues were; how much ligand needs to bind to how many
> receptors
> to see a response? Is there a linear dose response. For which the data is
> poor, at best. And finally, is there therefore a threshold dose? These are
> more relevant to risk assessment which seems to be the underlying theme of
> this list (i.e how much is too much?) Now you have your thinking hat on
> don't just jump on the nearest available explanation. Ask yourself the
> basic
> questions and go and look for the data. But you seem to be on the right
> track, FINALLY!!
>
>
> Louise
>
>
>
> MOLECULAR MECHANISM OF DIOXIN ACTION
>
> Halogenated aromatic hydrocarbons (HAHs), such as polychlorinated
> dibenzo-p-dioxins, biphenyls, dibenzofurans, and related compounds
> represent
> a diverse group of persistent, widespread environmental contaminants.
> 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD, dioxin), the most
> biologically-active and toxic member of this class of compounds produces a
> wide variety of species- and tissue-specific effects (1,2) including:
> tumor
> promotion, immuno- hepato- and dermal toxicity, lethality, birth defects,
> endocrine disruption and induction of numerous enzymes, most notably that
> of
> microsomal cytochrome P4501A1 and its associated monooxygenase activity,
> aryl hydrocarbon hydroxylase (AHH) (1,2). The P4501A1 isozyme contributes
> to
> the metabolic activation and detoxification of polycyclic aromatic
> hydrocarbons, many of which are carcinogens (3).
>
> The induction of hepatic AHH activity is perhaps the best studied of the
> biochemical effects resulting from exposure to TCDD and related HAHs
> (4,5).
> Early experiments examining the induction of AHH activity by a series of
> halogenated dibenzo-p-dioxin and dibenzofuran congeners resulted in the
> identification of a specific receptor which bound these compounds
> saturably
> and with high affinity. Qualitative structure-activity relationship
> studies
> revealed that the ability of a compound to bind to this receptor was well
> correlated not only with its ability to induce AHH activity (1,2,6) but
> also
> its ability to induce toxic effects, such as thymic involution, wasting
> and
> epidermal keratinization (1,2,6,7), suggesting that the receptor also
> mediates the toxicity of these compounds. This TCDD receptor has been
> identified and characterized in a wide variety of species and tissues
> (8,9)
> and has been designated as the aromatic hydrocarbon receptor (AhR).
>
> Induction of hepatic P450IA1-dependent AHH activity has been utilized as a
> model system to examine the molecular mechanism of action of HAHs. The
> current model for the AhR-dependent P4501A1 induction mechanism (above) is
> in several ways similar to that described for some steroid hormone
> receptors
> and steroid-responsive genes (10,11). The unliganded AhR complex exists in
> the cytosol complexed with at least three additional proteins (12).
> Following high affinity ligand (TCDD) binding, the TCDD:AhR complex
> undergoes a poorly defined process of transformation, during which hsp90
> (a
> heat shock protein of 90 kDa) and other proteins appear to dissociate from
> the TCDD:AhR complex, the AhR complex acquires the ability to bind to DNA
> with high affinity and transformed TCDD:AhR complexes subsequently
> accumulate within the nucleus (12-16). High affinity DNA binding of the
> AhR
> complex appears to require its association with at least one additional
> protein, the Ah receptor nuclear translocator (ARNT) protein (17-20). The
> binding of these transformed heteromeric TCDD:AhR complexes to specific
> DNA
> sequences (Dioxin Responsive Elements (DREs)) adjacent to the cytochrome
> P4501A1 (CYP1A1) gene leads to DNA bending, chromatin disruption,
> increased
> promoter accessibility and increased rates of transcription initiation of
> the CYP1A1 gene with the subsequent accumulation of cytochrome
> P450IA1-specific mRNA (4,21-27). The presence of the AhR complex in a wide
> variety of species and tissues and with its ability to act as a
> ligand-dependent transactivator of gene expression suggests that many of
> the
> toxic and biological effects of HAHs result from differential alteration
> of
> gene expression in susceptible cells.
>
>
> REFERENCES
> 1. Poland,A. and Knutson,J.C. (1982) 2,3,7,8-tetrachlorodibenzo-p-dioxin
> and
> related halogenated aromatic hydrocarbons: examination of the mechanism of
> toxicity, Ann. Rev. Pharmacol. Toxicol. 22, 517-554.
>
> 2. Safe,S.H. (1986) Comparative toxicology and mechanism of action of
> polychlorinated dibenzo-p-dioxins and dibenzofurans, Ann. Rev. Pharmacol.
> Toxicol. 26, 371-399.
>
> 3. Gelboin,H.V. (1980) Benzo[a]pyrene metabolism, activation and
> carcinogenesis: role and regulation of mixed-function oxidases and related
> enzymes, Physiol. Rev. 60, 1107-1166.
>
> 4. Whitlock,J.P. (1986) The regulation of cytochrome P-450 gene
> expression,
> Ann. Rev. Pharmacol. Toxicol. 26, 333-369.
>
> 5. Whitlock,J.P.,Jr. (1990) Genetic and Molecular Aspects of
> 2,3,7,8-tetrachlorodibenzo-p-dioxin action, Ann. Rev. Pharmacol. Toxicol.
> 30, 251-277.
>
> 6. Goldstein,J.A. and Safe,S. (1989) Mechanism of action and
> structure-activity relationships for the chlorinated dibenzo-p-dioxins and
> related compounds, in: Halogenated Biphenyls, Terphenyls, Naphthalenes,
> Dibenzodioxins and Related Products (Kimbrough,R.D. and Jensen,J., eds),
> pp.
> 239-293, Elsevier Science Pub, Amsterdam.
>
> 7. Knutson,J.C. and Poland,A. (1980) Keratinization of mouse teratoma cell
> line XB produced by 2,3,7,8-tetrachlorodibenzo-p-dioxin: an in vitro model
> of toxicity, Cell 22, 27-36.
>
> 8. Denison,M.S. and Wilkinson,C.F. (1985) Identification of the Ah
> receptor
> in selected mammalian species and induction of aryl hydrocarbon
> hydroxylase,
> Eur. J. Biochem. 147, 439-435.
>
> 9. Denison,M.S., Wilkinson,C.F. and Okey,A.B. (1986) Ah receptor for
> 2,3,7,8-tetrachlorodibenzo-p-dioxin: comparative studies in mammalian and
> nonmammalian species, Chemosphere 15, 1665-1672.
>
> 10. Yamamoto,K.R. (1985) Steroid receptor regulated transcription of
> specific genes and gene networks, Ann. Rev. Genet. 19, 209-252.
>
> 11. Carson-Jurica,M.A., Schrader,W.T. and O'Malley,B.M. (1990) Steroid
> receptor family: structure and functions, Endo. Rev. 11, 201-214.
>
> 12. Perdew,G.H. (1992) Chemical cross-linking of the cytosolic and nuclear
> forms of the Ah receptor in hepatoma line 1c1c7, Biochem. Biophys. Res.
> Comm. 182, 55-62.
>
> 13. Perdew,G.H. and Poland,A. (1988) Purification of the Ah receptor from
> C57BL/6J mouse liver, J. Biol. Chem., 263, 9848-9852.
>
> 14. Henry,E.C., Rucci,G. and Gasiewicz,T.A. (1989) Characterization of
> multiple forms of the Ah receptor: comparison of species and tissues,
> Biochem. 28, 6430-6440.
>
> 15. Whitlock,J.P., Jr. and Galeazzi,D.R. (1984)
> 2,3,7,8-Tetrachlorodibenzo-p-dioxin receptors in mouse hepatoma cells:
> nuclear location and strength of nuclear binding, J. Biol. Chem. 259,
> 980-985.
>
> 16. Henry,E.C. and Gasiewicz,T.A. (1993) Transformation of the aryl
> hydrocarbon receptor to a DNA-binding form is accompanied by release of
> the
> 90 kDa heat-shock protein and increased affinity for
> 2,3,7,8-tetrachlorodibenzo-p-dioxin, Biochem. J. 294, 95-101.
>
> 17. Dolwick,K.M., Schmidt,J.V., Carver,L.A., Swanson,H.I. and
> Bradfield,C.A.
> (1993) Cloning and expression of human Ah receptor cDNA, Molec. Pharm. 44,
> 911-917.
>
> 18. Whitelaw,M., Pongratz,I., Wilhelmsson,A., Gustafsson,J-A. and
> Poellinger,L. (1993) Ligand-dependent recruitment of the arnt coregulator
> determines DNA recognition by the dioxin receptor, Molec. Cell. Biol. 13,
> 2504-2514.
>
> 19. Probst,M.R., Reisz-Porszasz,S., Agbunag,R.V., Ong,M.S. and
> Hankinson,O.,
> (1993) Role of the aryl hydrocarbon receptor nuclear translocator protein
> in
> aryl hydrocarbon (dioxin) receptor action, Molec. Pharmacol. 44, 511-518.
>
> 20. Hoffman,E.C., Reyes,H., Chu,F-F., Sander,F., Conley,L.H., Brooks,B.A.
> and Hankinson,O. (1991) Cloning of a factor required for activity of the
> Ah
> (dioxin) receptor, Science 252, 954-958.
>
> 21. Denison,M.S., Fisher,J.M. and Whitlock,J.P.,Jr. (1988) Inducible,
> receptor-dependent protein-DNA interactions at a dioxin-responsive
> transcriptional enhancer, Proc. Natl. Acad. Sci. 85, 2528-2532.
>
> 22. Elferink,C.J. and Whitlock,J.P.,Jr. (1990)
> 2,3,7,8-Tetrachlorodibenzo-p-dioxin-inducible, Ah receptor-mediated
> bending
> of enhancer DNA, J. Biol. Chem. 265, 5718-5721.
>
> 23. Morgan,J. E. and Whitlock,J.P.,Jr. (1992) Transcription-dependent and
> transcription-independent nucleosome disruption induced by dioxin, Proc.
> Natl. Acad. Sci. USA 89,11622-11626.
>
> 24. Durrin,L.K. and Whitlock,J.P.,Jr. (1989)
> 2,3,7,8-Tetrachlorodibenzo-p-dioxin-inducible aryl hydrocarbon
> receptor-mediated change in CYP1A1 chromatin structure occurs independent
> of
> transcription, Mol.Cell. Biol. 9:5733-5737.
>
> 25. Wu,L. and Whitlock,J.P.Jr., (1992) Mechanism of dioxin action: Ah
> receptor-mediated increase in Promoter accessibility in vivo, Proc. Natl.
> Acad. Sci. 89, 4811-4815.
>
> 26. Denison,M.S., Fisher,J.M. and Whitlock,J.P.,Jr. (1988) The DNA
> recognition site for the dioxin-Ah receptor complex: nucleotide sequence
> and
> functional analysis, J. Biol. Chem. 263, 17221-17224.
>
> 27. Denison,M.S., Fisher,J.M. and Whitlock,J.P.,Jr. (1989) Protein-DNA
> interactions at recognition sites for the dioxin-Ah receptor complex, J.
> Biol. Chem. 264, 16478-16482.
>
>
>
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