Characterization of a serine protease-mediated cell death program activated in human leukemia cells

Tightly controlled proteolysis is a defining feature of apoptosis and caspases are critical in this regard. Significant roles for non-caspase proteases in cell death have been highlighted. Staurosporine causes a rapid induction of apoptosis in virtually all mammalian cell types. Numerous studies demonstrate that staurosporine can activate cell death under caspase-inhibiting circumstances. The aim of this study was to investigate the proteolytic mechanisms responsible for cell death under these conditions. To that end, we show that inhibitors of serine proteases can delay cell death in one such system. Furthermore, through profiling of proteolytic activation, we demonstrate, for the first time, that staurosporine activates a chymotrypsin-like serine protease-dependent cell death in HL-60 cells independently, but in parallel with the caspase controlled systems. Features of the serine protease-mediated system include cell shrinkage and apoptotic morphology, regulation of caspase-3, altered nuclear morphology, generation of an endonuclease and DNA degradation. We also demonstrate a staurosporine-induced activation of a putative 16 kDa chymotrypsin-like protein during apoptosis.     

Cys155 of 27 kDa maize gamma-zein is a key amino acid to improve its in vitro digestibility

Twenty-seven kilodalton gamma-zein is a subclass of the maize zein storage proteins and, due to its localization at the protein body periphery, is critical to digestibility characteristics of all zeins. This protein had low in vitro digestibility, presumably due to its high Cys content (7.35 mol%) that is similar to the hard-to-digest analogous sorghum protein, gamma-kafirin. Therefore, each of the conserved disulfide-bonded Cys' was mutated to create C144A, C148A, C155A, and C156A maize gamma-zein mutants. The C155A showed a remarkable increase in digestibility to proteases - pepsin, chymotrypsin, and trypsin. A high conservation of this Cys among cereal gamma-prolamins indicates the utility of this finding.     

Acute oxidative stress is associated with cell proliferation in the mouse liver

Oxidative stress is known to produce tissue injury and to activate various signaling pathways. To investigate the molecular events linked to acute oxidative stress in mouse liver, we injected a toxic dose of paraquat. Liver necrosis was first observed, followed by histological marks of cell proliferation. Concomitantly, activation of the MAP kinase pathway and increased levels of the anti-apoptotic protein Bcl-XL were observed. Gene expression profiles revealed that the differentially expressed genes were potentially involved in cell proliferation. These data suggest that paraquat-induced acute oxidative stress triggers the activation of regeneration-related events in the liver.     

Identification of TNF-alpha-responsive NF-kappaB p65-binding element in the distal promoter of the mouse serine protease inhibitor SerpinE2

Serine protease inhibitor SerpinE2 is known as a cytokine-inducible gene. Here, we investigated whether tumor necrosis factor alpha-(TNF-alpha)-induced expression of SerpinE2 is mediated by the nuclear factor-kappaB (NF-kappaB) p65 subunit. Both steady state and TNF-alpha-induced expression of SerpinE2 mRNA were abrogated in p65-/- murine embryonic fibroblasts (MEFs). Reconstitution with wild-type p65 rescued SerpinE2 mRNA expression in an IkappaB kinase beta-dependent manner. Electrophoresis mobility shift assay and ChIP assay demonstrated that p65 bound to the kappaB-like DNA sequence located at approximately -9 kbp in the SerpinE2 promoter. In addition, TNF-alpha stimulated luciferase gene expression driven by the kappaB-like element in the reconstituted MEFs, but not in p65-/- MEFs. These results indicated that activation of NF-kappaB p65 plays an important role in TNF-alpha-induced expression of SerpinE2.     

Peroxynitrite induces F-actin depolymerization and blockade of myosin ATPase stimulation

Treatment of F-actin with the peroxynitrite-releasing agent 3-morpholinosydnonimine (SIN-1) produced a dose-dependent F-actin depolymerization. This is due to released peroxynitrite because it is not produced by 'decomposed SIN-1', and it is prevented by superoxide dismutase concentrations efficiently preventing peroxynitrite formation. F-actin depolymerization has been found to be very sensitive to peroxynitrite, as exposure to fluxes as low as 50-100nM peroxynitrite leads to nearly 50% depolymerization in about 1h. G-actin polymerization is also impaired by peroxynitrite although with nearly 2-fold lower sensitivity. Exposure of F-actin to submicromolar fluxes of peroxynitrite produced cysteine oxidation and also a blockade of the ability of actin to stimulate myosin ATPase activity. Our results suggest that an imbalance of the F-actin/G-actin equilibrium can account for the observed structural and functional impairment of myofibrils under the peroxynitrite-mediated oxidative stress reported for some pathophysiological conditions.     

Heterologous expression, purification, and properties of a potato protein inhibitor of serine proteinases

The gene PKPI-B10 [AF536175] encoding in potato (Solanum tuberosum L., cv. Istrinskii) a Kunitz-type protein inhibitor of proteinases (PKPI) has been cloned into the pET23a vector and then expressed in Escherichia coli. The recombinant protein PKPI-B10 obtained as inclusion bodies was denatured, separated from admixtures by ion-exchange fast protein liquid chromatography (FPLC) on MonoQ under denaturing conditions, and renatured. The native protein was additionally purified by ion-exchange FPLC on DEAE-Toyopearl. The PKPI-B10 protein effectively inhibits the activity of trypsin, significantly weaker suppresses the activity of chymotrypsin, and has no effect on other serine proteinases: human leukocyte elastase, subtilisin Carlsberg, and proteinase K, and also the plant cysteine proteinase papain.     

On the interaction site of serine acetyltransferase in the cysteine synthase complex from Escherichia coli

Cysteine synthase from Escherichia coli is a bienzyme complex comprised of serine acetyltransferase (SAT) and O-acetylserine sulfhydrylase A. The site of interaction of a SAT molecule was investigated by gel chromatography and surface plasmon technique using various mutant-type SATs, to better understand the mechanism involved in complex formation. The C-terminus of SAT, Ile 273, along with Glu 268 and Asp 271, was found to be essential for complex formation. The effects of O-acetyl-L-serine and sulfide on the affinity for the complex formation were also studied using a surface plasmon technique.     

Structure-activity relationship of an alpha-toxin Bs-Tx28 from scorpion (Buthus sindicus) venom suggests a new alpha-toxin subfamily

Scorpion venoms are among the most widely known source of peptidyl neurotoxins used for callipering different ion channels, e.g., for Na(+), K(+), Ca(+) or Cl(-). An alpha-toxin (Bs-Tx28) has been purified from the venom of scorpion Buthus sindicus, a common yellow scorpion of Sindh, Pakistan. The primary structure of Bs-Tx28 was established using a combination of MALDI-TOF-MS, LC-ESI-MS, and automated Edman degradation analysis. Bs-Tx28 consists of 65 amino acid residues (7274.3+/-2Da), including eight cysteine residues, and shows very high sequence identity (82-94%) with other long-chain alpha-neurotoxins, active against receptor site-3 of mammalian (e.g., Lqq-IV and Lqh-IV from scorpions Leiurus sp.) and insect (e.g., BJalpha-IT and Od-1 from Buthotus judaicus and Odonthobuthus doriae, respectively) voltage-gated Na(+) channels. Multiple sequence alignment and phylogenetic analysis of Bs-Tx28 with other known alpha- and alpha-like toxins suggests the presence of a new and separate subfamily of scorpion alpha-toxins. Bs-Tx28 which is weakly active in both, mammals and insects (LD(50) 0.088 and 14.3microg/g, respectively), shows strong induction of the rat afferent nerve discharge in a dose-dependent fashion (EC(50)=0.01microg/mL) which was completely abolished in the presence of tetrodotoxin suggesting the binding of Bs-Tx28 to the TTX-sensitive Na(+)-channel. Three-dimensional structural features of Bs-Tx28, established by homology modeling, were compared with other known classical alpha-mammal (AaH-II), alpha-insect (Lqh-alphaIT), and alpha-like (BmK-M4) toxins and revealed subtle variations in the Nt-, Core-, and RT-CT-domains (functional domains) which constitute a "necklace-like" structure differing significantly in all alpha-toxin subfamilies. On the other hand, a high level of conservation has been observed in the conserved hydrophobic surface with the only substitution of W43 (Y43/42) and an additional hydrophobic character at position F40 (L40/A/V/G39), as compared to the other mentioned alpha-toxins. Despite major differences within the primary structure and activities of Bs-Tx28, it shares a common structural and functional motif (e.g., transRT-farCT) within the RT-CT domain which is characteristic of scorpion alpha-mammal toxins.