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Date of Award

2006

Document Type

Dissertation - Pacific Access Restricted

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Pharmaceutical and Chemical Sciences

First Advisor

William Chan

First Committee Member

James Uchizono

Second Committee Member

Craig Yierra

Third Committee Member

David Thomas

Fourth Committee Member

Roshanak Rahimian

Abstract

Upon ligand binding, the aryl hydrocarbon receptor (AhR) translocates into the nucleus and dimerizes with its partner Ah receptor nuclear translocator (Arnt). The AhR/Arnt heterodimer binds to the enhancer element DRE to regulate target gene expression. It is known that the formation of the ligand-dependent AhR/Arnt/DRE complex requires protein factors in vitro. The first aim is to determine whether two other Hsp90-associated proteins present in rabbit reticulocyte lysate (RRL), namely CyP40 and Hsp70, play any role in forming the AhR/Arnt/DRE complex. Fractionation and immunodepletion experiments revealed that Hsp70 is not necessary for the formation of this complex. In contrast, CYP40 is involved in forming the complex since (1) immunodepletion of CyP40 from a RRL fraction reduces the intensity of the AhR-Arnt-DRE complex by 48% and (2) recombinant human CyP40 alone causes the formation of this complex. In addition, CyP40-interacting proteins appear to be essential for the full CyP40 effect on the AhR gel shift complex. The second aim is to determine the role of β-tubulin in Amt-dependent signaling pathways. From the insect Sf9 cytosol, β-tubulin enriched fraction (F5) was isolated which suppresses the AhR/Arnt/DRE complex formation in a gel shift assay. Tubulin enriched from pig brain had a similar inhibition of the AhR gel shift complex, suggesting that β-tubulin in F5 is likely responsible for the action. Using the TALON resin, β-tubulin was co-precipitated with the baculovirus 6His-Arnt, showing that β-tubulin interacts with Arnt. β-tubulin was examined to decide its role in the hypoxia inducible factor-1α (HIF-1α) signaling which is also Arnt-dependent. Gel shift data using HIF-1α and Arnt showed that F5 suppressed the formation of the HIF-1α/Arnt/HRE complex. Subsequently the Sf9 β-tubulin was cloned and about 95% of its full-length sequence was identified. The amino acid sequence of Sf9 β-tubulin shares high sequence identity with human β-tubulin. Upon transient transfection of a plasmid containing a human β-tubulin cDNA into MGF7 or Hep3B cells, the HRE-driven luciferase activity was clearly suppressed. In conclusion, we have evidence supporting that β-tubulin inhibits the Arnt-dependent signaling and the mechanism may involve the interaction between Arnt and β-tubulin.

Pages

152

ISBN

9780542881312

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