Re: TRANSCRIPTIONAL REGULATION OF THE NAD(P)H:QUINONE OXIDOREDUCTASE 1 AND GLUTATHIO

December 22, 2008

anyone care to translate??? copper is not acting like the mercury and

lead, but that about all I could get out of this...tia, wishing all

the best, elizabeth

>

> TRANSCRIPTIONAL REGULATION OF THE NAD(P)H:QUINONE OXIDOREDUCTASE 1

> AND GLUTATHIONE S-TRANSFERASE YA GENES BY MERCURY, LEAD, AND COPPER

> Hesham M. Korashy, and Ayman O. S. El-Kadi

> Faculty of Pharmacy and Pharmaceutical Sciences, University of

> Alberta, Edmonton, Alberta, Canada

>

> Recently, we demonstrated the ability of heavy metals, particularly

> Hg2+, Pb2+, and Cu2+, to differentially modulate in Hepa 1c1c7 cells

> the expression of the phase II xenobiotic metabolizing enzymes NAD(P)

> H:quinone oxidoreductase 1 (Nqo1) and glutathione S-transferase

> subunit Ya (Gst ya) genes, yet the mechanisms involved remain

> unknown. To investigate the molecular mechanisms involved in the

> regulation of Nqo1 and Gst ya genes by heavy metals, Hepa 1c1c7 cells

> were treated with Hg2+, Pb2+, or Cu2+ in the presence and absence of

> 2,3,7,8-tetrachlorodibenzo-p-dioxin, a potent inducer of Nqo1, Gst

> ya, and Cyp1a1 genes. Analysis of the time-dependent effect of heavy

> metals revealed that Hg2+ and Pb2+ increased whereas Cu2+ inhibited

> the constitutive and inducible expression of Nqo1 and Gst ya mRNAs in

> a time-dependent manner. The RNA synthesis inhibitor actinomycin D

> significantly inhibited the Nqo1 and Gst ya mRNA induction in

> response to metals, indicating a requirement of de novo RNA

> synthesis. The protein synthesis inhibitor cycloheximide

> significantly inhibited metal-mediated induction of Nqo1 and Gst ya

> mRNAs, which coincided with a decrease in the nuclear factor

> erythroid 2-related factor 2 (Nrf2) protein expression, implying the

> requirement of Nrf2 protein synthesis for the induction of these

> genes. Furthermore, inhibition of Nrf2 protein degradation by

> carbobenzoxy-L-leucyl-L-leucyl-leucinal (MG-132), a 26S proteasome

> inhibitor, significantly reversed the cycloheximide-mediated

> inhibition of Nqo1 and Gst ya mRNAs, which coincided with an increase

> in the expression of Nrf2, confirming that a transcriptional

> mechanism is involved. Nqo1 and Gst ya mRNA and protein decay

> experiments revealed lack of post-transcriptional and post-

> translational mechanisms. This is the first demonstration that heavy

> metals regulate the expression of Nqo1 and Gst ya genes through a

> transcriptional mechanism.

>

December 22, 2008

Xenobiotic metabolism relates to how cells (or the human body) deal with

foreign chemicals such as drugs. There are generally three steps or

phases involved in metabolizing these chemicals. The enzymes studied,

Nqo1 and Gst ya, are involved in the second step. Hepa1c1c7 is a mouse

hepatoma cell that is frequently used in cell culture experiments.

Prior studies evidently showed that lead and mercury ions increase the

expression of the genes coding for these two enzymes, and this study set

out to find out how this is done. It is commonly believed that genes

are expressed by the creation of proteins (such as enzymes) by a process

of decoding the DNA on the gene by complementary strands of RNA, a

process called transcription. This process takes place in the nucleus

of the cell, prior to protein synthesis occuring outside of the nucleus.

By applying chemicals that are known to inhibit RNA synthesis, and

demonstrating that the effect of the inhibition was a decrease in the

expression of the genes and that it occurred in the nucleus, the authors

are able to infer that lead and mercury in some way influence the rate

or efficiency of transcription of the genes.

Jim

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From:

[mailto: ] On Behalf Of eli8591

Sent: Monday, December 22, 2008 1:06 PM

Subject: [ ] Re: TRANSCRIPTIONAL REGULATION OF THE

NAD(P)H:QUINONE OXIDOREDUCTASE 1 AND GLUTATHIO