Suguru Ito

Tumor promoting effect of podoplanin-positive fibroblasts is mediated by enhanced RhoA activity

There is growing evidence that stromal fibroblasts can promote tumor progression via several mechanisms. We previously reported that podoplanin (PDPN) expressed on stromal fibroblasts is functionally protein responsible for the promotion of tumor formation in mouse subcutaneous tissue. The purpose of the present study was to reveal the molecular mechanism by which PDPN on stromal fibroblasts promotes tumor formation. The subcutaneous co-injection of the human lung adenocarcinoma cell line A549 and human fibroblasts (hFbs) overexpressing wild-type podoplanin (WT-PDPN) promoted subcutaneous tumor formation, compared with the co-injection of A549 and control hFbs (64% vs 21%). On the other hand, hFbs expressing PDPN mutant in which the cytoplasmic domain of PDPN was deleted (PDPN-Del.IC), resulted in a relatively lower level of tumor formation (33%). Since PDPN reportedly regulates RhoA activity through its cytoplasmic domain, we measured the activation state of RhoA in hFbs expressing WT-PDPN. RhoA activity was 2.7-fold higher in WT-PDPN expressing hFbs than in control hFbs. Furthermore, the subcutaneous co-injection of hFbs expressing constitutive active RhoA (G14VRhoA) and A549 cells enhanced tumor formation compared with the co-injection of the same cell line and control hFbs. These results indicate that enhanced RhoA activity in hFbs expressing PDPN may be one of the mechanisms resulting in the promotion of tumor formation, suggesting that biomechanical remodeling of the microenvironment by stromal fibroblasts may play important roles in tumor progression.

Experimental realization of two-dimensional Dirac nodal line fermions in monolayer Cu 2 Si

Topological nodal line semimetals, a novel quantum state of materials, possess topologically nontrivial valence and conduction bands that touch at a line near the Fermi level. The exotic band structure can lead to various novel properties, such as long-range Coulomb interaction and flat Landau levels. Recently, topological nodal lines have been observed in several bulk materials, such as PtSn4, ZrSiS, TlTaSe2 and PbTaSe2. However, in two-dimensional materials, experimental research on nodal line fermions is still lacking. Here, we report the discovery of two-dimensional Dirac nodal line fermions in monolayer Cu2Si based on combined theoretical calculations and angle-resolved photoemission spectroscopy measurements. The Dirac nodal lines in Cu2Si form two concentric loops centred around the Γ point and are protected by mirror reflection symmetry. Our results establish Cu2Si as a platform to study the novel physical properties in two-dimensional Dirac materials and provide opportunities to realize high-speed low-dissipation devices.Nodal line semimetals have been observed in three-dimensional materials but are missing in two-dimensional counterparts. Here, Feng et al. report two-dimensional Dirac nodal line fermions protected by mirror reflection symmetry in monolayer Cu2Si.

Superconducting Network in Spatially Modulated Magnetic Field – Hofstadter-Type Problem in Checkerboard Field

The superconducting transition of a two-dimensional square network of Nb in a spatially modulated magnetic field, consisting of a uniform component and a sign-alternating (checkerboard pattern) component, has been studied. Evolution of the Little-Parks oscillation pattern as a function of the checkerboard field amplitude manifests some features of the low-energy envelopes of the corresponding Hofstadter butterfly-type diagrams.

Controlling the surface photovoltage on WSe2 by surface chemical modification

The surface photovoltage (SPV) effect is key to the development of opto-electronic devices such as solar-cells and photo-detectors. For the prototypical transition metal dichalcogenide WSe2, core level and valence band photoemission measurements show that the surface band bending of pristine cleaved surfaces can be readily modified by adsorption with K (an electron donor) or C60 (an electron acceptor). Time-resolved pump-probe photoemission measurements reveal that the SPV for pristine cleaved surfaces is enhanced by K adsorption, but suppressed by C60 adsorption, and yet the SPV relaxation time is substantially shortened in both cases. Evidently, adsorbate-induced electronic states act as electron-hole recombination centers that shorten the carrier lifetime.The surface photovoltage (SPV) effect is key to the development of opto-electronic devices such as solar-cells and photo-detectors. For the prototypical transition metal dichalcogenide WSe2, core level and valence band photoemission measurements show that the surface band bending of pristine cleaved surfaces can be readily modified by adsorption with K (an electron donor) or C60 (an electron acceptor). Time-resolved pump-probe photoemission measurements reveal that the SPV for pristine cleaved surfaces is enhanced by K adsorption, but suppressed by C60 adsorption, and yet the SPV relaxation time is substantially shortened in both cases. Evidently, adsorbate-induced electronic states act as electron-hole recombination centers that shorten the carrier lifetime.