No abstract

The distal-less homeobox gene 4 (DLX4) is a member of the DLX family of homeobox genes. Although absent from most normal adult tissues, DLX4 is widely expressed in leukemia, lung, breast, ovarian and prostate cancers. However the molecular targets, mechanisms and pathways that mediate the role of DLX4 in tumor metastasis are poorly understood. In this study, we found that DLX4 induces cancer cells to undergo epithelial to mesenchymal transition (EMT) through TWIST. Overexpression of DLX4 increased expression of TWIST expression in cancer cell lines, resulting in increased migratory and invasive capacity. Likewise, knocking down expression of DLX4 decreased TWIST expression and the migration ability of cancer cell lines. DLX4 bound to regulatory regions of the TWIST gene. Both western blotting and immunohistochemistry staining showed that the expression of DLX4 and TWIST are correlated in most of breast tumors. Taken together, these data from both cell models and tumor tissues demonstrate that DLX4 not only upregulates TWIST expression but also induces EMT and tumor metastasis. Altogether, we propose a new pathway in which DLX4 drives expression of TWIST to promote EMT, cancer migration, invasion and metastasis.

No abstract

Aquaporin Z (AqpZ) is an integral membrane protein that facilitates transport of water across Escherichia coli cells with a high rate. Previously, R189, a highly conserved residue of the selective filter of AqpZ, was proposed as a gate within the water channel on the basis of the observation of both open and closed conformations of its side chain in different monomers of an X-ray structure, and the observation of rapid switches between the two conformations in molecular dynamic simulations. However, the gating mechanism of the R189 side chain remains controversial since it is unclear whether the different conformations observed in the X-ray structure is due to different functional states or is a result of perturbation of non-native detergent environments. Herein, in native-like synthetic bilayers and native E. coli membranes, a number of solid-state NMR techniques are employed to examine gating mechanism of the R189 side chain of AqpZ. One R189 side-chain conformation is highly evident since only a set of peaks corresponding to the R189 side chain is observed in 2D N-C spectra. The immobility of the R189 side chain is detected by H-N dipolar lineshapes, excluding the possibility of the rapid switches between the two side-chain conformations. High-resolution monomeric structure of AqpZ, determined by CS-Rosetta calculations using experimentally measured distance restraints related to the R189 side chain, reveals that this side chain is in an open conformation, which is further verified by its water accessibility. All the solid-state NMR experimental results, combining with water permeability essay, suggest a permanently open conformation of the R189 side chain in the synthetic bilayer and native membranes. This study provides new structural insights into the gating mechanism of aquaporins and highlights the significance of lipid bilayer environments in elucidating the molecular mechanism of membrane proteins.