NOVEL FUNCTION OF mirnas IN REGULATING GENE EXPRESSION Ana M. Martinez
Switching from Repression to Activation: MicroRNAs can Up-Regulate Translation. Shoba Vasudevan, Yingchun Tong, Joan A. Steitz AU-rich elements (ARE) and microrna target sites are conserved sequences in mrna 3 UTR that control gene expression posttranscriptionally. Upon cell cycle arrest (G1 phase by serum starvation), the ARE in tumor necrosis factor a (TNFa) mrna is transformed into a translation activation signal, recruiting Argonaute (AGO) and fragile X mental retardation related protein 1 (FXR1).
PURPOSE 1. To identify if the binding of the AGO2-FXR1 complex that activates translation is directed by a mirna complementary to the ARE. 2. To see if micro-ribonucleoproteins (micrornps) can in general up regulate translation under growth-arrest conditions, thereby switching between repressing and activating roles in response to the cell cycle.
Human mir369-3 Its seed sequence is complementary to the 2 target sites (seed 1and 2) within the minimal TNFa ARE needed for translation activation of the luciferase reporter. Expression of the mirna is reduced in serum-grown cells. It is necessary for translation up-regulation of the ARE reporter.
mir369-3 associates with TNFa to upregulate translation by direct base pairing in the ARE region
Distinguishing translation repression HeLa cells were subjected to serum starvation and the released into serum growth conditions for 18 hours, which results in synchronous proliferation (in late S/G2 phase).
RNP purification of the aptamer-tagged ARE and mtare reporters show that requirement of the three proteins in the ARE for translation activation. Knockdown Experiments show that HMGA2 translation upregulation is also dependent on the presence of FXR1 and AGO2.
MicroRNA-373 induces expression of genes with complementary promoter sequences. Robert F. Place, Long-Cheng Li, Deepa Pookot, Emily J. Noonan and Rajvir Dahiya mirna controls up-regulation of gene expression by binding to complementary sequences on promoters. By scanning promoters in silico for sequences complementary to known mirnas, they found a putative mir-373 target within promoters of E- Cadherin and Cold-shock domain-containing protein C2(CSDC2) as well as many other proteins.
mirna-373 target sites on promoters of E-Cadherin and CSDC2
Synthesized the native mature duplex mir-373 and another dsrna molecule (dsecad-640) fully complementary to the mir-373 target site. Immunoblot analysis confirmed induction of E-Cadherin.
Up-Regulation of CSDC2 by mir-373 Determined that mir-373 acts in pleitropic manner, up-regulating gene expression of multiple genes.
Biogenesis of pre-mir373 by Dicer is required to induce E-Cadherin expression.
Enrichment of RNA Polymerase II at mir-373-targeted gene Promoters Performed ChiP assays, using an antibody specific to RNApII. Mapped Three regions corresponding to the transcription start sites of E-Cadherin and CSDC2.
Synthesis of two mir-373 mutants indicate that induction of E-Cadherin and CSDC2 is specific to the sequence of mir-373
Conclusion mirnas apart from repressing gene expression or degrading complementary mrna, can up-regulate translation of proteins by complementary base pairing with ARE in 3 UTRs of mrnas and recruiting the AGO2-FXR1 complex. Gene expression is also achieved by mirnas binding to complementary sequences in promoters of genes.