Maintaining cholesterol homeostasis: Sterol regulatory element-binding proteins

Figure 1 Feedforward and feedback effects of oxysterols FXR = farnesoid × receptor; LRH-1 = liver receptor homologue-1; LXR = liver × receptor; SF-1 = steroidogenic factor-1; SREBP = sterol responsive element binding protein.

Figure 2 Maturation of SREBPs -NH₂ = amino-terminal ends of SREBP or SCAP. S1P = Site-1 protease (crossed-out = inactive); S2P = Site-2 protease. SRE = sterol-responsive element; nSREBP = nuclear SREBP. Arrangement of the additional transcription factors NF-Y, Sp1, CREB, ARC, CBP, TBP, and DRIC (see text) is tentative as their requirements are not exactly known.

Figure 3 Metabolic pathways regulated by SREBPs G-6-P = glucose-6-phosphate; 6-PG = 6-phosphogluconate; Rib-5-P = ribulose-5-phosphate; PEP = phosphoenol pyruvate; CoA = coenzyme A; HMGCoA = 3-hydroxy-3-methylglutaryl coen-zyme A. SREBP-1c and SREBP-2 activate genes for the genera-tion of NADPH (ATP citrate lyase, malic enzyme, G-6-P dehydrogenase, 6-PG dehydrogenase) required in various steps of lipid synthesis.