miR-33 links SREBP-2 induction to repression of sterol transporters

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Abstract
The sterol regulatory element binding protein 2 (SREBP-2) and the liver X receptor (LXR) control antagonistic transcriptional programs that stimulate cellular cholesterol uptake and synthesis, and cholesterol efflux, respectively. The clinical importance of SREBP-2 is revealed in patients with hypercholesterolemia treated with statins, which reduce low-density lipoprotein (LDL) cholesterol levels by increasing hepatic expression of SREBP-2 and its target, the LDL receptor. Here we show that miR-33 is encoded within SREBP-2 and that both mRNAs are coexpressed. We also identify sequences in the 3′ UTR of ABCA1 and ABCG1, sterol transporter genes both previously shown to be regulated by LXR, as targets for miR-33–mediated silencing. Our data show that LXR-dependent cholesterol efflux to both ApoAI and serum is ameliorated by miR-33 overexpression and, conversely, stimulated by miR-33 silencing. Finally, we show that ABCA1 mRNA and protein and plasma HDL levels decline after hepatic overexpression of miR-33, whereas they increase after hepatic miR-33 silencing. These results suggest novel ways to manage hypercholesterolemic patients.