Chromium(VI) down-regulates heavy metal-induced metallothionein gene transcription by modifying transactivation potential of the key transcription factor, metal-responsive transcription factor 1.
The robust induction of metallothionein-I and II (MT-I and MT-II) genes by several heavy metals such as zinc and cadmium requires the specific transcription factor metal-responsive transcription factor 1 (MTF1). Chromium (VI), a major environmental carcinogen, not only failed to activate these genes but also inhibited their induction by Zn2+ or Cd2+. The heavy metal-induced expression of another MTF1 target gene, zinc transporter 1 (ZnT-1), was also down-regulated by Cr6+. By contrast, the expression of two MTF1-independent Cd2+-inducible genes, heme oxygenase 1 (HO-1) and HSP-70, was not sensitive to Cr6+. Cr6+ did not also affect the expression of housekeeping genes such as GAPDH or beta-actin. Stable cell lines overexpressing variable levels of MTF1, the key transactivator of the MT genes, demonstrated differential resistance toward the inhibitory effect of Cr6+, indicating MTF1 as a target of chromium toxicity. The basal and inducible binding of MTF1 to metal response elements was not affected by treatment of cells with Cr6+. Transient transfection studies showed that the ability of MTF1 to transactivate the MT-I promoter was significantly compromised by Cr6+. The fusion protein consisting of a Gal-4 DNA binding domain and one or more of the three transactivation domains of MTF1, namely the acidic domain, proline-rich domain, and serine-threonine rich domain, activated the GAL-4-driven luciferase gene to different degrees, but all were sensitive to Cr6+. MTF1 null cells were prone to apoptosis after exposure to Zn2+ or Cd2+ that was augmented in presence Cr6+, whereas the onset of apoptosis was significantly delayed in cells overexpressing MTF1.
Majumder
Sarmila
S
Department of Molecular and Cellular Biochemistry, The Ohio State University, College of Medicine, The Ohio State University, Columbus, Ohio 43210, USA.
Ghoshal
Kalpana
K
Summers
Dennis
D
Bai
Shoumei
S
Datta
Jharna
J
Jacob
Samson T
ST
D017304:Annexin A5 / Q000494:pharmacology; D017209:Apoptosis; D015152:Blotting, Northern; D015153:Blotting, Western; D002460:Cell Line; D002857:Chromium / Q000378:metabolism* / Q000494:pharmacology; D004396:Coloring Agents / Q000494:pharmacology; D018983:DNA Footprinting; D004268:DNA-Binding Proteins; D015536:Down-Regulation; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006419:Heme Oxygenase (Decyclizing) / Q000378:metabolism; D051547:Heme Oxygenase-1; D006801:Humans; D020287:In Situ Nick-End Labeling; D008565:Membrane Proteins; D008668:Metallothionein / Q000096:biosynthesis* / Q000235:genetics*; D019216:Metals, Heavy / Q000378:metabolism; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012190:Retroviridae / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013778:Tetrazolium Salts / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D015032:Zinc / Q000378:metabolism; D000097809:Transcription Factor MTF-1
D017304:Annexin A5; D002857:Chromium; D004396:Coloring Agents; D004268:DNA-Binding Proteins; D018840:HSP70 Heat-Shock Proteins; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1; D008565:Membrane Proteins; D008668:Metallothionein; D019216:Metals, Heavy; D011993:Recombinant Fusion Proteins; D013778:Tetrazolium Salts; D013844:Thiazoles; D014157:Transcription Factors; D015032:Zinc; D000097809:Transcription Factor MTF-1; C496541:HMOX1 protein, human; C022616:thiazolyl blue