Regulation of RIPK3- and RHIM-dependent Necroptosis by the Proteasome

Receptor-interacting protein kinase 3 (RIPK3) is a serine/threonine kinase with essential function in necroptosis. The activity of RIPK3 is controlled by phosphorylation. Once activated, RIPK3 phosphorylates and activates the downstream effector mixed lineage kinase domain-like (MLKL) to induce necroptosis. In certain situations, RIPK3 has also been shown to promote apoptosis or cytokine expression in a necroptosis and kinase-independent manner. The ubiquitin-proteasome system is the major pathway for selective degradation of cellular proteins and thus has a critical role in many cellular processes such as cell survival and cell death. Clinically, proteasome inhibition has shown promise as an anti-cancer agent. Here we show that the proteasome inhibitors MG132 and bortezomib activate the RIPK3-MLKL necroptotic pathway in mouse fibroblasts as well as human leukemia cells. Unlike necroptosis induced by classical TNF-like cytokines, necroptosis induced by proteasome inhibitors does not require caspase inhibition. However, an intact RIP homotypic interaction motif (RHIM) is essential. Surprisingly, when recruitment of MLKL to RIPK3 is restricted, proteasome inhibitors induced RIPK3-dependent apoptosis. Proteasome inhibition led to accumulation of K48-linked ubiquitinated RIPK3, which was partially reduced when Lys-264 was mutated. Taken together, these results reveal the ubiquitin-proteasome system as a novel regulatory mechanism for RIPK3-dependent necroptosis.     

miR-30a attenuates drug sensitivity to 5-FU by modulating cell proliferation possibly by downregulating cyclin E2 in oral squamous cell carcinoma

We aimed to determine the functional role of the miRNA, which affects drug sensitivity to 5-FU in oral squamous cell carcinoma (OSCC), using two types of 5-FU-resistant and parental OSCC cell lines. MiRNA microarray data showed that miR-30a was significantly upregulated in two resistant cell lines. Therefore, we investigated the effects and molecular mechanism of miR-30a on 5-FU sensitivity. Stable overexpression of miR-30a in parental OSCC cells decreased cell proliferation and attenuated drug sensitivity to 5-FU. Cell cycle analysis indicated that miR-30a overexpression increased the proportion of G1 phase cells and decreased the proportion of S phase cells. MiR-30a knockdown using siRNA reversed the effects of miR-30a overexpression. DNA microarray analysis using miR-30a-overexpressing cell lines and a TargetScan database search showed that cyclin E2 (CCNE2) is a target of miR-30a. A luciferase reporter assay confirmed that a miR-30a mimic interacted with the specific binding site in the 3' UTR of CCNE2. CCNE2 knockdown with siRNA in OSCC cells yielded decreased drug sensitivity to 5-FU, similar to miR-30a overexpressing cells. These findings suggest that miR-30a in OSCC may be a novel biomarker of 5-FU-resistant tumors, as well as a therapeutic target for combating resistance.     

Molecular dynamics simulation of self-assembled nanocubes in methanol

Molecular dynamics simulations were performed for the hexameric nanocubes of methylated (1₆) and demethylated (2₆) gear-shaped amphiphiles in pure methanol to reveal the difference in structural fluctuation between 1₆ and 2₆. Within our simulation time of 2.0 ns, the cubic structure of 1₆ in methanol is maintained, whereas that of 2₆ is collapsed. We found that the triple π-stacking moieties consisting of the three 3-pyridyl groups in 2₆ are more fluctuated than those in 1₆. This suggests that methyl groups serve to reduce structural fluctuation for nanocubes. We also found that the existence of the solvent molecules near the nanocube is an important factor for the collapse of the 2₆ structure.     

Engineering redox cofactor utilization for detoxification of glycolaldehyde, a key inhibitor of bioethanol production, in yeast Saccharomyces cerevisiae

Hot-compressed water treatment of lignocellulose liberates numerous inhibitors that prevent ethanol fermentation of yeast Saccharomyces cerevisiae. Glycolaldehyde is one of the strongest fermentation inhibitors and we developed a tolerant strain by overexpressing ADH1 encoding an NADH-dependent reductase; however, its recovery was partial. In this study, to overcome this technical barrier, redox cofactor preference of glycolaldehyde detoxification was investigated. Glycolaldehyde-reducing activity of the ADH1-overexpressing strain was NADH-dependent but not NADPH-dependent. Moreover, genes encoding components of the pentose phosphate pathway, which generates intracellular NADPH, was upregulated in response to high concentrations of glycolaldehyde. Mutants defective in pentose phosphate pathways were sensitive to glycolaldehyde. Genome-wide survey identified GRE2 encoding a NADPH-dependent reductase as the gene that confers tolerance to glycolaldehyde. Overexpression of GRE2 in addition to ADH1 further improved the tolerance to glycolaldehyde. NADPH-dependent glycolaldehyde conversion to ethylene glycol and NADP⁺ content of the strain overexpressing both ADH1 and GRE2 were increased at 5 mM glycolaldehyde. Expression of GRE2 was increased in response to glycolaldehyde. Carbon metabolism of the strain was rerouted from glycerol to ethanol. Thus, it was concluded that the overexpression of GRE2 together with ADH1 restores glycolaldehyde tolerance by augmenting the NADPH-dependent reduction pathway in addition to NADH-dependent reduction pathway. The redox cofactor control for detoxification of glycolaldehyde proposed in this study could influence strategies for improving the tolerance of other fermentation inhibitors.     

Isodichroic point and the β–random coil transition of poly(S-carboxymethyl-L-cysteine) and poly(S-carboxyethyl-L-cysteine) in the absence of added salt

The β-coil transition of poly(S-carboxymethyl-L -cysteine) (poly[Cys(CH₂CO₂H)]) and poly(S-carboxyethyl-L -cysteine) (poly[Cys((CH₂)₂CO₂H)]) was followed by CD, potentiometric titration, and viscosity in the absence of added salt. These different properties give consistent results for poly[Cys((CH₂)₂CO₂H)]. The CD spectra of poly[Cys(CH₂CO₂H)] change considerably with the degree of neutralization α even for a low-molecular-weight sample incapable of forming the β-structure. Because of the superposition of this additional effect, the dependence of CD on α is inconsistent with titration data for the case of poly[Cys(CH₂CO₂H)], particularly when the nπ transition is used to follow the β-coil transition. The change of CD inherent to the β-coil transition is characterized by an isodichroic point: 215 nm for poly[Cys((CH₂)₂CO₂H)] and 218 nm for poly[Cys(CH₂CO₂H)]. A criterion supporting the stacking of the pleated sheet is suggested based on the isodichroic point.     

PCR random mutagenesis into Escherichia coli serine acetyltransferase: isolation of the mutant enzymes that cause overproduction of L-cysteine and L-cystine due to the desensitization to feedback inhibition.

PCR random mutagenesis in the cysE gene encoding Escherichia coli serine acetyltransferase was employed to isolate the mutant enzymes that, due to a much less feedback inhibition by L-cysteine, cause overproduction of L-cysteine and L-cystine in the recombinant strains. The L-cysteine auxotrophic and non-utilizing E. coli strain was transformed with plasmids having the altered cysE genes. Then, several transformants overproducing L-cysteine were selected by detecting the halo formation of the L-cysteine auxotroph. The production test of amino acids and analysis of the catalytic property on the mutant enzymes suggest that the carboxy-terminal region of serine acetyltransferase plays an important role in the desensitization to feedback inhibition and the high level production of L-cysteine and L-cystine.     

Purification and characterization of monovalent cation-activated levodione reductase from Corynebacterium aquaticum M-13.

(6R)-2,2,6-Trimethyl-1,4-cyclohexanedione (levodione) reductase was isolated from a cell extract of the soil isolate Corynebacterium aquaticum M-13. This enzyme catalyzed regio- and stereoselective reduction of levodione to (4R,6R)-4-hydroxy-2,2, 6-trimethylcyclohexanone (actinol). The relative molecular mass of the enzyme was estimated to be 142,000 Da by high-performance gel permeation chromatography and 36,000 Da by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme required NAD(+) or NADH as a cofactor, and it catalyzed reversible oxidoreduction between actinol and levodione. The enzyme was highly activated by monovalent cations, such as K(+), Na(+), and NH(4)(+). The NH(2)-terminal and partial amino acid sequences of the enzyme showed that it belongs to the short-chain alcohol dehydrogenase/reductase family. This is the first report of levodione reductase.