Artificial structures made of stacked two-dimensional crystals have recently been the focus of intense research activity. As in twisted or stacked graphene layers, these structures can show unusual behaviours and new phenomena. Among the various layered compounds that can be exfoliated, transition-metal dichalcogenides exhibit interesting properties governed by their structural symmetry and interlayer coupling, which are highly susceptible to stacking. Here, we obtain-by folding exfoliated MoS2 monolayers-MoS2 bilayers with different stacking orders, as monitored by second harmonic generation and photoluminescence. Appropriate folding can break the inversion symmetry and suppress interlayer hopping, evoking strong valley and spin polarizations that are not achieved in natural MoS2 bilayers of Bernal stacking. It can also enlarge the indirect bandgap by more than 100 meV through a decrease in the interlayer coupling. Our work provides an effective and versatile means to engineer transition-metal dichalcogenide materials with desirable electronic and optical properties.

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Histone deacetylases (HDACs) are major epigenetic modulators involved in a broad spectrum of human diseases including cancers. As HDACs are promising targets of cancer therapy, it is important to understand the mechanisms of HDAC regulation. In this study, we show that ubiquitin-specific peptidase 4 (USP4) interacts directly with and deubiquitinates HDAC2, leading to the stabilization of HDAC2. Accumulation of HDAC2 in USP4-overexpression cells leads to compromised p53 acetylation as well as crippled p53 transcriptional activation, accumulation and apoptotic response upon DNA damage. Moreover, USP4 targets HDAC2 to downregulate tumor necrosis factor TNFα-induced nuclear factor (NF)-κB activation. Taken together, our study provides a novel insight into the ubiquitination and stability of HDAC2 and uncovers a previously unknown function of USP4 in cancers.

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REV3Lp, the catalytic subunit of DNA polymerase zeta, is the major participant in translesion DNA synthesis. Recent evidence suggests that REV3L has an important role in the maintenance of genome stability despite its mutagenic characteristics. Such a function makes it a cancer susceptibility candidate gene. To investigate association between REV3L polymorphisms and lung cancer risk in a Chinese population, we first genotyped 15 common polymorphisms of the REV3L gene and found that three single nucleotide polymorphisms (rs465646, rs459809 and rs1002481) were significantly associated with lung cancer risk. One of the strongest associations observed was for the 3'-terminal untranslated region (3'UTR) 460 T>C polymorphism (rs465646) (adjusted odds ratio (OR)=0.69 for TC/CC; P=0.007, compared with TT). Similar results were obtained in a subsequent replication study (adjusted OR=0.72; P=0.016). Combined data from the two studies of 1072 lung cancer patients and 1064 cancer-free controls generated an even stronger association (adjusted OR=0.71; P=3.04 × 10(-4)). This 3'UTR 460 T>C variant was predicted to modulate the binding of several micro RNAs. Surface plasmon resonance analysis and luciferase assays showed that the T allele demonstrated a stronger binding affinity for miR-25 and miR-32, resulting in significantly weaker reporter expression levels. Additional experiments revealed that miR-25/32 could downregulate endogenous REV3L. Furthermore, the tumor-suppressing role of REV3L was confirmed by the foci formation assay. These results support our hypothesis that the REV3L rs465646 variant modifies lung cancer susceptibility in Chinese Han population by affecting miRNA-mediated gene regulation.

Excitons play a dominant role in the optoelectronic properties of atomically thin van der Waals (vdW) semiconductors. These excitons are amenable to on-demand engineering with diverse control knobs, including dielectric screening, interlayer hybridization, and moiré potentials. However, external stimuli frequently yield heterogeneous excitonic responses at the nano- and meso-scales, making their spatial characterization with conventional diffraction-limited optics a formidable task. Here, we use a scattering-type scanning near-field optical microscope (s-SNOM) to acquire exciton spectra in atomically thin transition metal dichalcogenide microcrystals with previously unattainable 20 nm resolution. Our nano-optical data revealed material- and stacking-dependent exciton spectra of MoSe2, WSe2, and their heterostructures. Furthermore, we extracted the complex dielectric function of these prototypical vdW semiconductors. s-SNOM hyperspectral images uncovered how the dielectric screening modifies excitons at length scales as short as few nanometers. This work paves the way towards understanding and manipulation of excitons in atomically thin layers at the nanoscale.

Second harmonic generation (SHG) is a nonlinear optical response arising exclusively from broken inversion symmetry in the electric‐dipole limit. Recently, SHG has attracted widespread interest as a versatile and noninvasive tool for characterization of crystal symmetry and emerging ferroic or topological orders in quantum materials. However, conventional far‐field optics is unable to probe local symmetry at the deep subwavelength scale. Here, near‐field SHG imaging of 2D semiconductors and heterostructures with the spatial resolution down to 20 nm is demonstrated using a scattering‐type nano‐optical apparatus. It is shown that near‐field SHG efficiency is greatly enhanced by excitons in atomically thin transition metal dichalcogenides. Furthermore, by correlating nonlinear and linear scattering‐type nano‐imaging, nanoscale variations of interlayer stacking order in bilayer WSe2 are resolved, and the stacking‐tuned excitonic light–matter interactions are revealed. This work demonstrates nonlinear optical interrogation of crystal symmetry and structure–property relationships at the nanometer length scales relevant to emerging properties in quantum materials.