Spastin is required for human immunodeficiency virus-1 efficient replication through cooperation with the endosomal sorting complex required for transport (ESCRT) protein.

Human immunodeficiency virus-1 (HIV-1) encodes simply 15 proteins and thus depends on multiple host cellular factors for virus reproduction. Spastin, a microtubule severing protein, is an identified HIV-1 dependency factor, but the mechanism regulating HIV-1 is unclear. Here, the study showed that knockdown of spastin inhibited the production of the intracellular HIV-1 Gag protein and new virions through enhancing Gag lysosomal degradation. Further investigation showed that increased sodium tolerance 1 (IST1), the subunit of endosomal sorting complex required for transport (ESCRT), could interact with the MIT domain of spastin to regulate the intracellular Gag production. In summary, spastin is required for HIV-1 replication, while spastin-IST1 interaction facilitates virus production by regulating HIV-1 Gag intracellular trafficking and degradation. Spastin may serve as new target for HIV-1 prophylactic and therapy.

Injection-free multiwavelength electroluminescence devices based on monolayer semiconductors driven by an alternating field.

Two-dimensional (2D) semiconductors have emerged as promising candidates for various optoelectronic devices especially electroluminescent (EL) devices. However, progress has been hampered by many challenges including metal contacts and injection, transport, and confinement of carriers due to small sizes of materials and the lack of proper double heterostructures. Here, we propose and demonstrate an alternative approach to conventional current injection devices. We take advantage of large exciton binding energies in 2D materials using impact generation of excitons through an alternating electric field, without requiring metal contacts to 2D materials. The conversion efficiency, defined as the ratio of the emitted photons to the preexisting carriers, can reach 16% at room temperature. In addition, we demonstrate the first multiwavelength 2D EL device, simultaneously operating at three wavelengths from red to near-infrared. Our approach provides an alternative to conventional current-based devices and could unleash the great potential of 2D materials for EL devices.

Reconstructing Local Profile of Exciton-Emission Wavelengths across a WS2 Bubble beyond the Diffraction Limit.

Air bubbles formed between layers of two-dimensional (2D) materials not only are unavoidable but also emerge as an important means of engineering their excitonic emission properties, especially as controllable quantum light sources. Measuring the actual spatially resolved optical properties across such bubbles is important for understanding excitonic physics and for device applications; however, such a measurement is challenging due to nanoscale features involved which require spatial resolution beyond the diffraction limit. Additional complexity is the involvement of multiple physical effects such as mechanical strain and dielectric environment that are difficult to disentangle. In this paper, we demonstrate an effective approach combining micro-photoluminescence measurement, atomic force microscope profile mapping, and a theoretical strain model. We succeeded in reconstructing the actual spatial profiles of the emission wavelengths beyond the diffraction limit for bubbles formed by a monolayer tungsten disulfide on boron nitride. The agreements and consistency among various approaches established the validity of our approach. In addition, our approach allows us to disentangle the effects of strain and dielectric environment and provides a general and reliable method to determine the true magnitude of wavelength changes due to the individual effects across bubbles. Importantly, we found that micro-optical measurement underestimates the red and blue shifts by almost 5 times. Our results provide important insights into strain and screening-dependent optical properties of 2D materials on the nanometer scale and contribute significantly to our understanding of excitonic emission physics as well as potential applications of bubbles in optoelectronic devices.

Excitonic complexes and optical gain in two-dimensional molybdenum ditelluride well below the Mott transition.

Semiconductors that can provide optical gain at extremely low carrier density levels are critically important for applications such as energy efficient nanolasers. However, all current semiconductor lasers are based on traditional semiconductor materials that require extremely high density levels above the so-called Mott transition to realize optical gain. The new emerging 2D materials provide unprecedented opportunities for studying new excitonic physics and exploring new optical gain mechanisms at much lower density levels due to the strong Coulomb interaction and co-existence and mutual conversion of excitonic complexes. Here, we report a new gain mechanism involving charged excitons or trions in electrically gated 2D molybdenum ditelluride well below the Mott density. Our combined experimental and modelling study not only reveals the complex interplay of excitonic complexes well below the Mott transition but also establishes 2D materials as a new class of gain materials at densities 4-5 orders of magnitude lower than those of conventional semiconductors and provides a foundation for lasing at ultralow injection levels for future energy efficient photonic devices. Additionally, our study could help reconcile recent conflicting results on 2D materials: While 2D material-based lasers have been demonstrated at extremely low densities with spectral features dominated by various excitonic complexes, optical gain was only observed in experiments at densities several orders of magnitude higher, beyond the Mott density. We believe that our results could lead to more systematic studies on the relationship between the mutual conversion of excitonic species and the existence of optical gain well below the Mott transition.

Lysine-specific demethylase 1 cooperates with BRAF-histone deacetylase complex 80 to enhance HIV-1 Tat-mediated transactivation.

Despite the notable success of combination antiretroviral therapy, how to eradicate latent HIV-1 from reservoirs poses a challenge. The Tat protein plays an indispensable role in HIV reactivation and histone demethylase LSD1 promotes Tat-mediated long terminal repeats (LTR) activation. However, the role of LSD1 in remodeling chromatin and the role of its component BHC80 in activation of latent HIV-1 in T cells are unknown. Our findings indicate that LSD1 could decrease the level of histone H3 lysine 4 trimethylation (H3K4me3) at the HIV-1 promoter by recruiting histone lysine demethylase 5A (KDM5A) and preventing histone methyltransferase Set1A and WD-40 repeat protein 5 (WDR5) from binding to LTR. Moreover, BHC80 is necessary for LSD1-triggered LTR activation and assists LSD1 in activating LTR by binding to nucleotides 305-631 of LTR. In activated J-Lat-A2 cells, BHC80 expression was elevated and its isoform BHC80-6 promoted the association of BHC80 with LSD1. These results suggest that the LSD1-BHC80 complex enhances HIV-1 transcription by a decrease of H3K4me3 level at the viral promoter. Therefore, it might be used as a new drug target to reactivate latent HIV-1.

HIV-1 Protein Tat1-72 Impairs Neuronal Dendrites via Activation of PP1 and Regulation of the CREB/BDNF Pathway.

Despite the success of combined antiretroviral therapy in recent years, the prevalence of human immunodeficiency virus (HIV)-associated neurocognitive disorders in people living with HIV-1 is increasing, significantly reducing the health-related quality of their lives. Although neurons cannot be infected by HIV-1, shed viral proteins such as transactivator of transcription (Tat) can cause dendritic damage. However, the detailed molecular mechanism of Tat-induced neuronal impairment remains unknown. In this study, we first showed that recombinant Tat (1-72 aa) induced neurotoxicity in primary cultured mouse neurons. Second, exposure to Tat1-72 was shown to reduce the length and number of dendrites in cultured neurons. Third, Tat1-72 (0-6 h) modulates protein phosphatase 1 (PP1) expression and enhances its activity by decreasing the phosphorylation level of PP1 at Thr320. Finally, Tat1-72 (24 h) downregulates CREB activity and CREB-mediated gene (BDNF, c-fos, Egr-1) expression. Together, these findings suggest that Tat1-72 might impair cognitive function by regulating the activity of PP1 and the CREB/BDNF pathway.

Room-temperature continuous-wave lasing from monolayer molybdenum ditelluride integrated with a silicon nanobeam cavity.

Monolayer transition-metal dichalcogenides (TMDs) have the potential to become efficient optical-gain materials for low-energy-consumption nanolasers with the smallest gain media because of strong excitonic emission. However, until now TMD-based lasing has been realized only at low temperatures. Here we demonstrate for the first time a room-temperature laser operation in the infrared region from a monolayer of molybdenum ditelluride on a silicon photonic-crystal cavity. The observation is enabled by the unique combination of a TMD monolayer with an emission wavelength transparent to silicon, and a high-Q cavity of the silicon nanobeam. The laser is pumped by a continuous-wave excitation, with a threshold density of 6.6 W cm-2. Its linewidth is as narrow as 0.202 nm with a corresponding Q of 5,603, the largest value reported for a TMD laser. This demonstration establishes TMDs as practical materials for integrated TMD-silicon nanolasers suitable for silicon-based nanophotonic applications in silicon-transparent wavelengths.

Study of the particles' structure dependent rheological behavior for polymer nanospheres based shear thickening fluid.

A novel kind of shear thickening fluid (STF) was developed via dispersing poly(styrene-acrylic acid) (PS-AA) nanospheres into ethylene glycol (EG). By varying the structure characteristics of the PS-AA particles, STFs with different rheological properties can be obtained. Firstly, the influence of the styrene/acrylic acid ratio on the PS-AA nanospheres was investigated. It was found that the higher ratio often led to the better shear thickening (ST) effects and under the optimum condition the maximum viscosity of the STF could reach to 152Pa s, while the ST effects decreased under further increasing the monomer ratio. Then, the divinyl benzene (DVB) was introduced to increase the cross-link density of the PS-AA. In comparison with the non-cross-link PS-AA nanospheres, the poly(styrene-acrylic acid-divinyl benzene) (PS-AA-DVB) based STFs exhibited much higher ST effects and the maximum viscosity was up to 385Pas when the DVB was only increased to 0.3%. In combination of the rheological properties and the structure characterization, a possible mechanism for the ST behavior was proposed and the influence of the particles' characteristics on the mechanical performance of the PS-AA based STF was carefully analyzed.