Sequence-Independent Logical Regulation of the Assembly and Disassembly of DNA Polyhedra.

Controlling the self-assembly of DNA nanostructures using rationally designed logic gates is a major goal of dynamic DNA nanotechnology, which could facilitate the development of biomedicine, molecular computation, et al. In previous works, the regulations mostly relied on either toehold-mediated strand displacement or stimuli-driven conformational switch, requiring elaborately-designed or specific DNA sequences. Herein, we reported a facile, base-sequence-independent strategy for logically controlling DNA self-assembly through external molecules. The INHIBIT and XOR logic controls over the assembly/disassembly of DNA polyhedra were realized through cystamine (Cyst) and ethylenediamine (EN) respectively, which were further integrated into a half subtractor circuit thanks to the sharing of the same inputs. Our work provides a sequence-independent strategy in logically controlling DNA self-assembly, which may open up new possibilities for dynamic DNA nanotechnology.

Boosted Productivity in Single-Tile-Based DNA Polyhedra Assembly by Simple Cation Replacement.

Cations such as divalent magnesium ion (Mg2+ ) play an essential role in DNA self-assembly. However, the strong electrostatic shielding effect of Mg2+ would be disadvantageous in some situations that require relatively weak interactions to allow a highly reversible error-correcting mechanism in the process of assembly. Herein, by substituting the conventional divalent Mg2+ with monovalent sodium ion (Na+ ), we have achieved one-pot high-yield assembly of tile-based DNA polyhedra at micromolar concentration of tiles, at least 10 times higher than the DNA concentrations reported previously. This strategy takes advantage of coexisting counterions and is expected to surmount the major obstacle to potential applications of such DNA nanostructures: large-scale production.

Forkhead Transcription Factor 3a (FOXO3a) Modulates Hypoxia Signaling via Up-regulation of the von Hippel-Lindau Gene (VHL).

FOXO3a, a member of the forkhead homeobox type O (FOXO) family of transcriptional factors, regulates cell survival in response to DNA damage, caloric restriction, and oxidative stress. The von Hippel-Lindau (VHL) tumor suppressor gene encodes a component of the E3 ubiquitin ligase complex that mediates hypoxia-inducible factor α degradation under aerobic conditions, thus acting as one of the key regulators of hypoxia signaling. However, whether FOXO3a impacts cellular hypoxia stress remains unknown. Here we show that FOXO3a directly binds to the VHL promoter and up-regulates VHL expression. Using a zebrafish model, we confirmed the up-regulation of vhl by foxo3b, an ortholog of mammalian FOXO3a Furthermore, by employing the clustered regularly interspaced short palindromic repeats (CRISPR)-associated RNA-guided endonuclease Cas9 (CRISPR/Cas9) technology, we deleted foxo3b in zebrafish and determined that expression of hypoxia-inducible genes was affected under hypoxia. Moreover, foxo3b-null zebrafish exhibited impaired acute hypoxic tolerance, resulting in death. In conclusion, our findings suggest that, by modulating hypoxia-inducible factor activity via up-regulation of VHL, FOXO3a (foxo3b) plays an important role in survival in response to hypoxic stress.

ELL targets c-Myc for proteasomal degradation and suppresses tumour growth.

Increasing evidence supports that ELL (eleven-nineteen lysine-rich leukaemia) is a key regulator of transcriptional elongation, but the physiological function of Ell in mammals remains elusive. Here we show that ELL functions as an E3 ubiquitin ligase and targets c-Myc for proteasomal degradation. In addition, we identify that UbcH8 serves as a ubiquitin-conjugating enzyme in this pathway. Cysteine 595 of ELL is an active site of the enzyme; its mutation to alanine (C595A) renders the protein unable to promote the ubiquitination and degradation of c-Myc. ELL-mediated c-Myc degradation inhibits c-Myc-dependent transcriptional activity and cell proliferation, and also suppresses c-Myc-dependent xenograft tumour growth. In contrast, the ELL(C595A) mutant not only loses the ability to inhibit cell proliferation and xenograft tumour growth, but also promotes tumour metastasis. Thus, our work reveals a previously unrecognized function for ELL as an E3 ubiquitin ligase for c-Myc and a potential tumour suppressor.

FBXO32 Targets c-Myc for Proteasomal Degradation and Inhibits c-Myc Activity.

FBXO32 (MAFbx/Atrogin-1) is an E3 ubiquitin ligase that is markedly up-regulated in muscle atrophy. Although some data indicate that FBXO32 may play an important role in tumorigenesis, the molecular mechanism of FBXO32 in tumorigenesis has been poorly understood. Here, we present evidence that FBXO32 targets the oncogenic protein c-Myc for ubiquitination and degradation through the proteasome pathway. Phosphorylation of c-Myc at Thr-58 and Ser-62 is dispensable for FBXO32 to induce c-Myc degradation. Mutation of the lysine 326 in c-Myc reduces c-Myc ubiquitination and prevents the c-Myc degradation induced by FBXO32. Furthermore, overexpression of FBXO32 suppresses c-Myc activity and inhibits cell growth, but knockdown of FBXO32 enhances c-Myc activity and promotes cell growth. Finally, we show that FBXO32 is a direct downstream target of c-Myc, highlighting a negative feedback regulation loop between c-Myc and FBXO32. Thus, FBXO32 may function by targeting c-Myc. This work explains the function of FBXO32 and highlights its mechanisms in tumorigenesis.

EAF2 suppresses hypoxia-induced factor 1α transcriptional activity by disrupting its interaction with coactivator CBP/p300.

Previous studies revealed that the potential tumor suppressor EAF2 binds to and stabilizes pVHL, suggesting that EAF2 may function by disturbing the hypoxia signaling pathway. However, the extent to which EAF2 affects hypoxia and the mechanisms underlying this activity remain largely unknown. In this study, we found that EAF2 is a hypoxia response gene harboring the hypoxia response element (HRE) in its promoter. By taking advantage of the pVHL-null cell lines RCC4 and 786-O, we demonstrated that hypoxia-induced factor 1α (HIF-1α), but not HIF-2α, induced EAF2 under hypoxia. Subsequent experiments showed that EAF2 bound to and suppressed HIF-1α but not HIF-2α transactivity. In addition, we observed that EAF2 inhibition of HIF-1α activity resulted from the disruption of p300 recruitment and that this occurred independently of FIH-1 (factor inhibiting HIF-1) and Sirt1. Furthermore, we found that EAF2 protected cells against hypoxia-induced cell death and inhibited cellular uptake of glucose under hypoxic conditions, suggesting that EAF2 indeed may act by modulating the hypoxia-signaling pathway. Our findings not only uncover a unique feedback regulation loop between EAF2 and HIF-1α but also provide a novel insight into the mechanism of EAF2 tumor suppression.