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Figure 1 Regulation of cholesterol synthesis. Inhibition of HMG CoA reductase reduces intracellular cholesterol levels, thus activating a protease, which in turn cleaves sterol regulatory element-binding proteins (SREBPs) from the endoplasmic reticulum. The SREBPs translocate to the nucleus where they upregulate expression of the LDL receptor gene. Enhanced LDL receptor expression increases receptor-mediated endocytosis of LDL and thus lowers serum LDL. Inhibition of HMG CoA reductase also reduces intracellular levels of isoprenoids, which are intermediates in cholesterol biosynthesis.