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Journal of Lipid Research, Vol. 45, 981-988, May 2004
Copyright © 2004 by American Society for Biochemistry and Molecular Biology

Sterol and fatty acid regulatory pathways in a Giardia lamblia-derived promoter

Tilla S. Worgall^1,*,, Sara R. Davis-Hayman^**, Marissa M. Magana, Peter M. Oelkers, Fernando Zapata, Rebecca A. Juliano, Timothy F. Osborne, Theodore E. Nash^** and Richard J. Deckelbaum^,

^* Department of Pathology, Columbia University, New York, NY 10032
Department of Pediatrics, Columbia University, New York, NY 10032
Institute of Human Nutrition, Columbia University, New York, NY 10032
^** Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892
Department of Molecular Biology and Biochemistry, University of California at Irvine, Irvine, CA 92697
Department of Bioscience and Biotechnology, Drexel University, Philadelphia, PA 19104

¹ To whom correspondence should be addressed. e-mail: tpw7{at}columbia.edu

The sterol regulatory element binding-proteins (SREBPs) are transcription factors that regulate the genes of lipid metabolism. Cholesterol and unsaturated fatty acids regulate SREBPs. Giardia lamblia (GL) is an intestinal parasite and one of the earliest derived members within the eukaryotic lineage. GLs exist as trophozoites and cysts. Growth in cholesterol depletion induces transcription of cyst-wall protein (CWP) genes that are upregulated during encystation. The hypothesis was investigated that SREBP-like pathways have a role in cwp gene transcription. Chinese hamster ovary cells were transfected with a cwp-2 promoter reporter construct. Incubation with cholesterol or oleate reduced cwp-2 mediated gene transcription to about half of the control. Incubation in sterol-depleted media, or in the presence of either an inhibitor of intracellular cholesterol movement or inhibitor of cholesterol synthesis, increased gene expression up to 3-fold. Overexpression of SREBPs increased reporter gene activity 2.5-fold. In the absence of functional SREBPs, cwp-2 was not regulated by cholesterol. Footprint analysis of cwp-2 reveals three novel binding sites for mammalian SREBPs with no homologies in other species or humans.

The data show that SREBP binds to and can modulate transcription of a regulatory element from an ancient eukaryote and suggest the existence of an SREBP homolog in GL.

Abbreviations: CHO, Chinese hamster ovary; CWP, cyst wall protein; GL, Giardia lamblia; mSREBP, mature SREBP; RLU, relative light units; SRE, sterol regulatory element; SREBP, sterol regulatory element binding protein

Supplementary key words cyst-wall protein • encystations • sterol regulatory element binding protein

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