Degree Name

PhD (Doctor of Philosophy)

Program

Biomedical Sciences

Date of Award

12-2014

Committee Chair or Co-Chairs

Alok Agrawal

Committee Members

Antonio Rusinol, David Johnson, Douglas Thewke, Richard Kostrzewa, Gregory Ordway

Abstract

Human C-reactive protein (CRP) is the prototypic acute phase protein whose serum concentration increases rapidly during inflammation. CRP is also associated with atherosclerosis; it is deposited at lesion sites where it may interact with modified lipoproteins. There are 2 major questions regarding CRP: 1. How is the serum concentration of CRP regulated? 2. What are the functions of CRP in atherosclerosis?

Our first aim was to determine the role of the constitutively expressed transcription factor Oct-1 in regulating CRP gene expression. We found that Oct-1 overexpression inhibited (IL-6+IL-1β)- induced CRP gene expression; maximal inhibition required the binding of Oct-1 to an octamer motif at (-59 to -66) on the CRP promoter. Oct-1 overexpression inhibited both (IL-6+IL-1β)- induced and C/EBPβ-induced CRP gene expression even when the Oct-1 site was deleted. These findings suggest that Oct-1 is a repressor of CRP gene expression that acts via binding to its cognate site on the CRP promoter as well as through indirect interactions with other promoterbound transcription factors.

Our second aim was to investigate the interaction of CRP with oxidized low density lipoprotein (ox-LDL). Acidic pH, a hallmark of atherosclerotic lesions, reversibly alters CRP structure and exposes a hidden binding site that enables CRP to bind ox-LDL. Using site-directed mutagenesis we constructed a CRP mutant (E42Q) that showed significant binding to ox-LDL at physiological pH. E42Q CRP required a less acidic pH for maximal binding and bound ox-LDL more efficiently than wild type CRP at any pH. We then examined if reactive oxygen species also induced CRP – ox-LDL interaction. H2O2-treated CRP bound ox-LDL at physiological pH. Like acidic pH, H2O2-treatment induced only a local structural change exposing the ox-LDL binding site. E42Q and H2O2-modified CRP are tools to study the function of CRP in animal models of atherosclerosis, which may not have an inflammatory environment sufficient to modify CRP and induce binding to atherogenic ox-LDL.

We conclude that Oct-1 is one of the critical regulators of CRP gene expression, and that CRP can be modified in vitro to convert it into an atherogenic LDL-binding molecule.

Document Type

Dissertation - unrestricted

Copyright

Copyright by the authors.

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