No abstract

Proper coordination of cholesterol biosynthesis and trafficking is essential to human health. The sterol regulatory element binding proteins (SREBPs) are key transcription regulators of genes involved in cholesterol biosynthesis/uptake. We show here that microRNAs (miR-33a/b) embedded within introns of the SREBP genes target the ATP-binding cassette transporter A1 (ABCA1), an important regulator of high-density lipoprotein (HDL) synthesis and reverse cholesterol transport, for post-transcriptional repression. Antisense inhibition of miR-33 in cell lines causes upregulation of ABCA1 expression and increased cholesterol efflux, and injection of mice on a western-type diet with locked nucleic acid (LNA)-antisense oligonucleotides results in elevated plasma HDL. Collectively, our findings indicate that miR-33 acts in concert with the SREBP host genes to control cholesterol homeostasis, and suggest that miR-33 may represent a therapeutic target for ameliorating cardiometabolic diseases.

MicroRNAs (miRNAs) have recently emerged as key regulators of metabolism. For example, miR-33a and b play a crucial role in controlling cholesterol and lipid metabolism in concert with their host genes, the SREBP transcription factors. Metabolic miRNAs such as miR-103 and miR-107 regulate insulin and glucose homeostasis, while others, such as miR-34a, may be key regulators of hepatic lipid homeostasis. The discovery of circulating miRNAs has highlighted their potential as both endocrine signalling molecules and disease markers. Dysregulation of miRNAs may contribute to metabolic abnormalities, suggesting that miRNAs may potentially serve as therapeutic targets to ameliorate cardiometabolic disorders.

The C-terminal domain (CTD) of RNA polymerase II (RNAPII) is an essential component of transcriptional regulation and RNA processing of protein-coding genes. A large body of data also implicates the CTD in the transcription and processing of RNAPII-mediated small nuclear RNAs (snRNAs). However, the identity of the complex (or complexes) that associates with the CTD and mediates the processing of snRNAs has remained elusive. Here, we describe an RNA polymerase II complex that contains at least 12 novel subunits, termed the Integrator, in addition to core RNAPII subunits. Two of the Integrator subunits display similarities to the subunits of the cleavage and polyadenylation specificity factor (CPSF) complex. We show that Integrator is recruited to the U1 and U2 snRNA genes and mediates the snRNAs' 3' end processing. The Integrator complex is evolutionarily conserved in metazoans and directly interacts with the C-terminal domain of the RNA polymerase II largest subunit.