Angiogenesis can aggravate gastric cancer progression. LncRNAs exert important roles in regulating various cancer behaviors. However, the functions and mechanisms of lncRNAs in angiogenesis remain largely unknown. Here we demonstrated that lncRNA PVT1 was upregulated and significantly associated with high-microvessel density and poor prognosis in gastric cancer. Through gain- and loss-of PVT1 expression, we found PVT1 could obviously induce angiogenesis within tumors, in addition to promoting tumor growth in vitro and in vivo. Mechanistically, PVT1 directly interacted with the signal transducer activator phospho-STAT3 in the nucleus, and increased its protein stability by protecting it from poly-ubiquitination and proteasome-dependent degradation. The binding of PVT1 activated the STAT3 signalling pathway, and successively elevated VEGFA expression to stimulate angiogenesis. The positive correlation of PVT1 and VEGFA expression was also verified in gastric cancer specimens, and high levels of PVT1 and VEGFA in combination frequently predicted shorter survival time. Moreover, we revealed that PVT1 was a STAT3-responsive lncRNA, as STAT3 could occupy the PVT1 promoter to facilitate its transcription. The positive feed-back loop of PVT1 and STAT3 continuously enhanced the oncogenic effects. Collectively, our study first elucidates the mechanism of PVT1-mediated angiogenesis via evoking the STAT3/VEGFA signalling axis, which provides promising target for developing new therapeutic strategy in gastric cancer.

We study the spin-excitation spectrum (dynamic structure factor) of the spin-1=2 square-lattice Heisenberg antiferromagnet and an extended model (the J-Q model) including four-spin interactions Q in addition to the Heisenberg exchange J. Using an improved method for stochastic analytic continuation of imaginary-time correlation functions computed with quantum Monte Carlo simulations, we can treat the sharp (δ-function) contribution to the structure factor expected from spin-wave (magnon) excitations, in addition to resolving a continuum above the magnon energy. Spectra for the Heisenberg model are in excellent agreement with recent neutron-scattering experiments on CuðDCOOÞ 2 · 4D 2 O, where a broad spectral-weight continuum at wave vector q ¼ ðπ; 0Þ was interpreted as deconfined spinons, i.e., fractional excitations carrying half of the spin of a magnon. Our results at ðπ; 0Þ show a similar reduction of the magnon weight and a large continuum, while the continuum is much smaller at q ¼ ðπ=2; π=2Þ (as also seen experimentally). We further investigate the reasons for the small magnon weight at ðπ; 0Þ and the nature of the corresponding excitation by studying the evolution of the spectral functions in the J-Q model. Upon turning on the Q interaction, we observe a rapid reduction of the magnon weight to zero, well before the system undergoes a deconfined quantum phase transition into a nonmagnetic spontaneously dimerized state. Based on these results, we reinterpret the picture of deconfined spinons at ðπ; 0Þ in the experiments as nearly deconfined spinons-a precursor to deconfined quantum criticality. To further elucidate the picture of a fragile ðπ; 0Þ-magnon pole in the Heisenberg model and its depletion in the J-Q model, we introduce an effective model of the excitations in which a magnon can split into two spinons that do not separate but fluctuate in and out of the magnon space (in analogy to the resonance between a photon and a particle-hole pair in the exciton-polariton problem). The model can reproduce the reduction of magnon weight and lowered excitation energy at ðπ; 0Þ in the Heisenberg model, as well as the energy maximum and smaller continuum at ðπ=2; π=2Þ. It can also account for the rapid loss of the ðπ; 0Þ magnon with increasing Q and the remarkable persistence of a large magnon pole at q ¼ ðπ=2; π=2Þ even at the deconfined critical point. The fragility of the magnons close to ðπ; 0Þ in the Heisenberg model suggests that various interactions that likely are important in many materials-e.g., longer-range pair exchange, ring exchange, and spin-phonon interactions-may also destroy these magnons and lead to even stronger spinon signatures than in CuðDCOOÞ 2 · 4D 2 O.

Recently, significant progress has been made in (2 þ 1)-dimensional conformal field theories without supersymmetry. In particular, it was realized that different Lagrangians may be related by hidden dualities; i.e., seemingly different field theories may actually be identical in the infrared limit. Among all the proposed dualities, one has attracted particular interest in the field of strongly correlated quantum-matter systems: the one relating the easy-plane noncompact CP 1 model (NCCP 1 ) and noncompact quantum electrodynamics (QED) with two flavors (N ¼ 2) of massless two-component Dirac fermions. The easyplane NCCP 1 model is the field theory of the putative deconfined quantum-critical point separating a planar (XY) antiferromagnet and a dimerized (valence-bond solid) ground state, while N ¼ 2 noncompact QED is the theory for the transition between a bosonic symmetry-protected topological phase and a trivial Mott insulator. In this work, we present strong numerical support for the proposed duality. We realize the N ¼ 2 noncompact QED at a critical point of an interacting fermion model on the bilayer honeycomb lattice and study it using determinant quantum Monte Carlo (QMC) simulations. Using stochastic series expansion QMC simulations, we study a planar version of the S ¼ 1=2 J-Q spin Hamiltonian (a quantum XY model with additional multispin couplings) and show that it hosts a continuous transition between the XY magnet and the valence-bond solid. The duality between the two systems, following from a mapping of their phase diagrams extending from their respective critical points, is supported by the good agreement between the critical exponents according to the proposed duality relationships. In the J-Q model, we find both continuous and first-order transitions, depending on the degree of planar anisotropy, with deconfined quantum criticality surviving only up to moderate strengths of the anisotropy. This explains previous claims of no deconfined quantum criticality in planar two-component spin models, which were in the stronganisotropy regime, and opens doors to further investigations of the global phase diagram of systems hosting deconfined quantum-critical points.