Date of Award
Doctor of Philosophy (PhD)
Precise regulation of cholesterol levels is necessary for survival of individual cells and the normal functioning of multicellular organisms. Many of the genes important in these processes are regulated at a transcriptional level by the sterol regulatory element binding proteins (SREBPs) and liver X receptors (LXRs). This thesis describes the identification by microarray technology of novel genes in cholesterol metabolism and the characterization of two of these genes. Microarray analysis of the livers of mice fed a low versus high cholesterol diet identified 37 down-regulated and 32 up-regulated genes. Confirmation of these genes and analysis in transgenic and pharmacologically treated mice identified three novel putative SREBP target genes and three novel putative LXR target genes. One of the down-regulated genes, Proprotein convertase subtilisin kexin 9 (Pcsk9) was cloned from mouse liver. Pcsk9 was found to be synthesized as a pro-form in the endoplasmic reticulum (ER) and expressed as a processed form in the trans-Golgi network. In mice, Pcsk9 was found to be expressed mainly in the liver. Overexpression of Pcsk9 in vivo demonstrated that Pcsk9 post-transcriptionally down-regulates low density lipoprotein receptor (LDLR) levels leading to elevated plasma LDL cholesterol. Furthermore, it was determined that Pcsk9 induces the degradation of the LDLR by a non-proteasomal mechanism in a post-ER compartment. One of the up-regulated genes, A disintegrin and metalloprotease 11 (Adam11) was cloned from mouse liver and a novel isoform with an alternative C-terminal tail was characterized. Adam11 was determined to be a cell surface protein expressed in multiple tissue types. Finally, preliminary functional studies with Adam11 indicate a potential role in LXR transcriptional activity and/or apolipoprotein B metabolism.
Maxwell, Kara Noelle, "Microarray Analysis Identifies Novel Cholesterol Regulated Genes, Including Pcsk9 Which Regulates LDL Receptor Function and LDL Cholesterol Levels" (2006). Student Theses and Dissertations. 417.