Actinonin induces apoptosis in U937 leukemia cells

Angiogenic and Arthritogenic Properties of the Soluble Form of CD13

Aminopeptidase N/CD13 is expressed by fibroblast-like synoviocytes (FLS) and monocytes (MNs) in inflamed human synovial tissue (ST). This study examined the role of soluble CD13 (sCD13) in angiogenesis, MN migration, phosphorylation of signaling molecules, and induction of arthritis. The contribution of sCD13 was examined in angiogenesis and MN migration using sCD13 and CD13-depleted rheumatoid arthritis (RA) synovial fluids (SFs). An enzymatically inactive mutant CD13 and intact wild-type (WT) CD13 were used to determine whether its enzymatic activity contributes to the arthritis-related functions. CD13-induced phosphorylation of signaling molecules was determined by Western blotting. The effect of sCD13 on cytokine secretion from RA ST and RA FLS was evaluated. sCD13 was injected into C57BL/6 mouse knees to assess its arthritogenicity. sCD13 induced angiogenesis and was a potent chemoattractant for MNs and U937 cells. Inhibitors of Erk1/2, Src, NF-κB, Jnk, and pertussis toxin, a G protein-coupled receptor inhibitor, decreased sCD13-stimulated chemotaxis. CD13-depleted RA SF induced significantly less MN migration than sham-depleted SF, and addition of mutant or WT CD13 to CD13-depleted RA SF equally restored MN migration. sCD13 and recombinant WT or mutant CD13 had similar effects on signaling molecule phosphorylation, indicating that the enzymatic activity of CD13 had no role in these functions. CD13 increased the expression of proinflammatory cytokines by RA FLS, and a CD13 neutralizing Ab inhibited cytokine secretion from RA ST organ culture. Mouse knee joints injected with CD13 exhibited increased circumference and proinflammatory mediator expression. These data support the concept that sCD13 plays a pivotal role in RA and acute inflammatory arthritis.

Inhibition of human mitochondrial peptide deformylase causes apoptosis in c-myc-overexpressing hematopoietic cancers

Inhibition of human mitochondrial peptide deformylase (HsPDF) depolarizes the mitochondrial membrane, reduces mitochondrial protein translation and causes apoptosis in Burkitt's lymphoma. We showed that HsPDF mRNA and protein levels were overexpressed in cancer cells and primary acute myeloid leukemia samples. Myc regulates mitochondria and metabolism; we also demonstrated c-myc regulated the expression of HsPDF, likely indirectly. Inhibition of HsPDF by actinonin blocked mitochondrial protein translation and caused apoptotic death of myc-positive Burkitt's lymphoma, but not myc-negative B cells. Inhibition of mitochondrial translation by chloramphenicol or tetracycline, structurally different inhibitors of the mitochondrial ribosome, which is upstream of deformylase activity, followed by treatment with actinonin, resulted in reversal of the biochemical events and abrogation of the apoptosis induced by actinonin. This reversal was specific to inhibitors of HsPDF. Inhibition of HsPDF resulted in a mitochondrial unfolded protein response (increased transcription factors CHOP and CEB/P and the mitochondrial protease Lon), which may be a mechanism mediating cell death. Therefore, HsPDF may be a therapeutic target for these hematopoietic cancers, acting via a new mechanism.

Structures of Staphylococcus aureus peptide deformylase in complex with two classes of new inhibitors

Peptide deformylase (PDF) catalyzes the removal of the formyl group from the N-terminal methionine residue in newly synthesized polypeptides, which is an essential process in bacteria. Four new inhibitors of PDF that belong to two different classes, hydroxamate/pseudopeptide compounds [PMT387 (7a) and PMT497] and reverse-hydroxamate/nonpeptide compounds [PMT1039 (15e) and PMT1067], have been developed. These compounds inhibited the growth of several pathogens involved in respiratory-tract infections, such as Streptococcus pneumoniae, Moraxella catarrhalis and Haemophilus influenzae, and leading nosocomial pathogens such as Staphylococcus aureus and Klebsiella pneumoniae with a minimum inhibitory concentration (MIC) in the range 0.1-0.8 mg ml(-1). Interestingly, the reverse-hydroxamate/nonpeptide compounds showed a 250-fold higher antimicrobial activity towards S. aureus, although the four compounds showed similar K(i) values against S. aureus PDF enzymes, with K(i) values in the 11-85 nM range. To provide a structural basis for the discovery of additional PDF inhibitors, the crystal structures of S. aureus PDF in complex with the four inhibitors were determined at resolutions of 1.90-2.30 Å. The inhibitor-bound structures displayed distinct deviations depending on the inhibitor class. The distance between the Zn(2+) ion and the carbonyl O atom of the hydroxamate inhibitors (or the hydroxyl O atom of the reverse-hydroxamate inhibitors) appears to be correlated to S. aureus inhibition activity. The structural information reported in this study should aid in the discovery of new PDF inhibitors that can be used as novel antibacterial drugs.

Inhibition of human peptide deformylase disrupts mitochondrial function

Deformylases are metalloproteases in bacteria, plants, and humans that remove the N-formyl-methionine off peptides in vitro. The human homolog of peptide deformylase (HsPDF) resides in the mitochondria, along with its putative formylated substrates; however, the cellular function of HsPDF remains elusive. Here we report on the function of HsPDF in mitochondrial translation and oxidative phosphorylation complex biogenesis. Functional HsPDF appears to be necessary for the accumulation of mitochondrial DNA-encoded proteins and assembly of new respiratory complexes containing these proteins. Consequently, inhibition of HsPDF reduces respiratory function and cellular ATP levels, causing dependence on aerobic glycolysis for cell survival. A series of structurally different HsPDF inhibitors and control peptidase inhibitors confirmed that inhibition of HsPDF decreases mtDNA-encoded protein accumulation. Therefore, HsPDF appears to have a role in maintenance of mitochondrial respiratory function, and this function is analogous to that of chloroplast PDF.

Structure and activity of human mitochondrial peptide deformylase, a novel cancer target

Peptide deformylase proteins (PDFs) participate in the N-terminal methionine excision pathway of newly synthesized peptides. We show that the human PDF (HsPDF) can deformylate its putative substrates derived from mitochondrial DNA-encoded proteins. The first structural model of a mammalian PDF (1.7 A), HsPDF, shows a dimer with conserved topology of the catalytic residues and fold as non-mammalian PDFs. The HsPDF C-terminus topology and the presence of a helical loop (H2 and H3), however, shape a characteristic active site entrance. The structure of HsPDF bound to the peptidomimetic inhibitor actinonin (1.7 A) identified the substrate-binding site. A defined S1' pocket, but no S2' or S3' substrate-binding pockets, exists. A conservation of PDF-actinonin interaction across PDFs was observed. Despite the lack of true S2' and S3' binding pockets, confirmed through peptide binding modeling, enzyme kinetics suggest a combined contribution from P2'and P3' positions of a formylated peptide substrate to turnover.

Indian black scorpion (Heterometrus bengalensis Koch) venom induced antiproliferative and apoptogenic activity against human leukemic cell lines U937 and K562

Venoms are rich source of several bioactive compounds that possess therapeutic potentials. The different constituents of scorpion venom can modulate cell proliferation, cell growth and cell cycle. In the present communication, the cytotoxic activity of Indian black scorpion (Heterometrus bengalensis) venom was explored on human leukemic U937 and K562 cells. Scorpion venom induced U937 and K562 cell growth inhibition and the IC(50) value calculated to be 41.5 microg/ml (U937) and 88.3 microg/ml (K562). The scorpion venom showed characteristic features of apoptosis such as membrane blebbing, chromatin condensation and DNA degradation in both the cells as evidenced by confocal, fluorescence, scanning electron microscopy. Scorpion venom (IC(50) dose, 48 h) induced DNA fragmentation as evidenced by comet formation. Flow-cytometric assay revealed a significant amount of apoptotic cells (early and late) due to scorpion venom treatment. The venom induced cell cycle arrest was observed with maximum cell accumulation at sub-G(1) phase. Thus, the Indian scorpion (H. bengalensis) venom possessed antiproliferative, cytotoxic and apoptogenic activity against human leukemic cells.

Venom of Indian monocellate cobra and Russell's viper show anticancer activity in experimental models

Indian monocellate cobra (Naja kaouthia) and Russell's viper (Vipera russelli) are common snakes of the East Indian sub-peninsula. The anticarcinogenic activities of their crude venoms were studied on carcinoma, sarcoma and leukemia models. Sub-lethal doses of venoms showed cytotoxicity on Ehrlich ascites carcinoma (EAC) cells in vivo. The venoms increased lifespan of EAC mice and strengthened the impaired host antioxidant system. Sarcoma formation in mice (3-methylcholanthrene induced) after venom treatment was significantly less (p < 0.005). Histopathological examination of tumors showed tissue necrosis. The venoms displayed potent cytotoxic and apoptogenic effect on human leukemic cells (U937/K562). The venoms reduced cell proliferation rate (p < 0.005) and produced morphological alterations indicative of apoptosis induction. Different degree and nature of anticarcinogenic property of cobra and viper venoms may be attributed to the difference in their constituents.

Aminopeptidase N (CD13) Regulates Tumor Necrosis Factor-α-induced Apoptosis in Human Neutrophils

Neutrophil apoptosis plays a central role in the resolution of granulocytic inflammation. We have shown previously that tumor necrosis factor-alpha (TNFalpha) enhances the rate of neutrophil apoptosis at early time points via a mechanism involving both TNF receptor (TNFR) I and TNFRII. Here we reveal a marked but consistent variation in the magnitude of the pro-apoptotic effect of TNFalpha in neutrophils isolated from healthy donors, and we show that inhibition of cell surface aminopeptidase N (APN) using actinonin, bestatin, or inhibitory peptides significantly enhanced the efficacy of TNFalpha-induced killing. Notably, an inverse correlation is shown to exist between neutrophil APN activity and the sensitivity of donor cells to TNFalpha-induced apoptosis. Inhibition of cell surface APN appears to interfere with the shedding of TNFRI, and as a consequence results in augmented TNFalpha-induced apoptosis, cell polarization, and TNFalpha-primed, formyl-methionyl-leucyl-phenylalanine-stimulated respiratory burst. Of note, actinonin and bestatin had no effect on TNFRII expression under resting or TNFalpha-stimulated conditions and did not alter CXCRI or CXCRII expression. These data suggest significant variation in the activity of APN/CD13 on the cell surface of neutrophils in normal individuals and reveal a novel mechanism whereby APN/CD13 regulates TNFalpha-induced apoptosis via inhibition of TNFRI shedding. This has therapeutic relevance for driving neutrophil apoptosis in vivo.