Gelation Behaviors and Mechanism of Silk Fibroin According to the Addition of Nitrate Salts.

Silk fibroin (SF) is a typical fibrous protein that is secreted by silkworms and spiders. It has been used in a variety of areas, and especially for tissue-engineering scaffolds, due to its sound processability, mechanical properties, biodegradability, and biocompatibility. With respect to gelation, the SF gelation time is long in aqueous solutions, so a novel approach is needed to shorten this time. The solubility of regenerated SF is sound in formic acid (FA), which is a carboxylic acid of the simplest structure. In this study, SF was dissolved in formic acid, and the addition of salts then induced a rapid gelation that accompanied a solution-color change. Based on the gelation behaviors of the SF solution according to different SF and salt concentrations, the gelation mechanism was investigated.

Development of episomal vectors carrying a nourseothricin-resistance marker for use in minimal media for Schizosaccharomyces pombe.

In the post-genomic era, an immediate challenge is to assign biological functions to novel proteins encoded by the genome. This challenge requires the use of a simple organism as a genetic tool and a range of new high-throughput techniques. Schizosacchromyces pombe is a powerful model organism used to investigate disease-related genes and provides useful tools for the functional analysis of heterologous genes. To expand the current array of experimental tools, we constructed two series of Sz. pombe expression vectors, i.e. general and Gateway vectors, containing nourseothricin-resistance markers. Vectors carrying nourseothricin-resistance markers possess advantages in that they do not limit the parental strains with auxotrophic mutations with respect to availability for use in clone selection and can be used together with vectors carrying nutrient markers in minimal media. We modified the pSLF173, pSLF273 and pSLF373 vectors carrying a triple haemagglutinin epitope (3×HA) and an Ura4 marker. The vectors described here contain the nmt1 promoter with three different episomal expression strengths for proteins fused with 3×HA, EGFP or DsRed at the N-terminus. These vectors represent an important contribution to the genome-wide investigation of multiple heterologous genes and for functional and genetic analysis of novel human genes.

Reactive oxygen species-mediated activation of the Akt/ASK1/p38 signaling cascade and p21(Cip1) downregulation are required for shikonin-induced apoptosis.

Shikonin derivatives exert powerful cytotoxic effects, induce apoptosis and escape multidrug resistance in cancer. However, the diverse mechanisms underlying their anticancer activities are not completely understood. Here, we demonstrated that shikonin-induced apoptosis is caused by reactive oxygen species (ROS)-mediated activation of Akt/ASK1/p38 mitogen-activated protein kinase (MAPK) and downregulation of p21(Cip1). In the presence of shikonin, inactivation of Akt caused apoptosis signal-regulating kinase 1 (ASK1) dephosphorylation at Ser83, which is associated with ASK1 activation. Shikonin-induced apoptosis was enhanced by inhibition of Akt, whereas overexpression of constitutively active Akt prevented apoptosis through modulating ASK1 phosphorylation. Silencing ASK1 and MKK3/6 by siRNA reduced the activation of MAPK kinases (MKK) 3/6 and p38 MAPK, and apoptosis, respectively. Antioxidant N-acetyl cysteine attenuated ASK1 dephosphorylation and p38 MAPK activation, indicating that shikonin-induced ROS is involved in the activation of Akt/ASK1/p38 pathway. Expression of p21(Cip1) was significantly induced in early response, but gradually decreased by prolonged exposure to shikonin. Overexpression of p21(Cip1) have kept cells longer in G1 phase and attenuated shikonin-induced apoptosis. Depletion of p21(Cip1) facilitated shikonin-induced apoptosis, implying that p21(Cip1) delayed shikonin-induced apoptosis via G1 arrest. Immunohistochemistry and in vitro binding assays showed transiently altered localization of p21(Cip1) to the cytoplasm by shikonin, which was blocked by Akt inhibition. The cytoplasmic p21(Cip1) actually binds to and inhibits the activity of ASK1, regulating the cell cycle progression at G1. These findings suggest that shikonin-induced ROS activated ASK1 by decreasing Ser83 phosphorylation and by dissociation of the negative regulator p21(Cip1), leading to p38 MAPK activation, and finally, promoting apoptosis.