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The Journal of Biological Chemistry (JBC) has been a major vehicle for disseminating and recording the discovery and characterization of proteolytic enzymes. The pace of discovery in the protease field accelerated during the 1971-2010 period that Dr. Herb Tabor served as the JBC's editor-in-chief. When he began his tenure, the fine structure and kinetics of only a few proteases were known; now thousands of proteases have been characterized, and over 600 genes for proteases have been identified in the human genome. In this review, besides reflecting on Dr. Tabor's invaluable contributions to the JBC and the American Society for Biochemistry and Molecular Biology (ASBMB), I endeavor to provide an overview of the extensive history of protease research, highlighting a few discoveries and roles of proteases in vivo. In addition, metalloproteinases, particularly meprins of the astacin family, will be discussed with regard to structural characteristics, regulation, mechanisms of action, and roles in health and disease. Proteases and protein degradation play crucial roles in living systems, and I briefly address future directions in this highly diverse and thriving research area. [ABSTRACT FROM AUTHOR]

Reactive oxygen species (ROS), continuously generated as by-products of respiration, inflict more damage on the mitochondrial (mt) than on the nuclear genome because of the nonchromatinized nature and proximity to the ROS source of the mitochondrial genome. Such damage, particularly single-strand breaks (SSBs) with 5′-blocking deoxyribose products generated directly or as repair intermediates for oxidized bases, is repaired via the base excision/SSB repair pathway in both nuclear and mt genomes. Here, we show that EXOG, a 5′-exo/endonuclease and unique to the mitochondria unlike FEN1 or DNA2, which, like EXOG, has been implicated in the removal of the 5′-blocking residue, is required for repairing endogenous SSBs in the mt genome. EXOG depletion induces persistent SSBs in the mtDNA, enhances ROS levels, and causes apoptosis in normal cells but not in mt genome-deficient rho0 cells. Thus, these data show for the first time that persistent SSBs in the mt genome alone could provide the initial trigger for apoptotic signaling in mammalian cells. [ABSTRACT FROM AUTHOR]

The article discusses the suicidal roles of lysosomes, that are described as suicide bags, in cellular processes. It states that lysosomes are linked to three major morphologically distinct pathways of cell death including apoptosis, type II programmed cell death or autophagic cell death, and necrosis. Furthermore, it mentions that lysosomes, regardless of their destructive potential, should not be called suicide bags because cell death happens mainly during pathologies.

Hsp27 inhibits mitochondrial injury and apoptosis in both normal and cancer cells by an unknown mechanism. To test the hypothesis that Hsp27 decreases apoptosis by inhibiting Bax, Hsp27 expression was manipulated in renal epithelial cells before transient metabolic stress, an insult that activates Bax, induces mitochondrial injury, and causes apoptosis. Compared with control, enhanced Hsp27 expression inhibited conformational Bax activation, oligomerization, and translocation to mitochondria, reduced the leakage of both cytochrome c and apoptosis-inducing factor, and significantly improved cell survival by >50% after stress. In contrast, Hsp27 down-regulation using RNA-mediated interference promoted Bax activation, increased Bax translocation, and reduced cell survival after stress. Immunoprecipitation did not detect Hsp27-Bax interaction before, during, or after stress, suggesting that Hsp27 indirectly inhibits Bax. During stress, Hsp27 expression prevented the inactivation of Akt, a pro-survival kinase, and increased the interaction between Akt and Bax, an Akt substrate. In contrast, Hsp27 RNA-mediated interference promoted Akt inactivation during stress. Hsp27 up- or down-regulation markedly altered the activity of phosphatidylinositol 3-kinase (PI3-kinase), a major regulator of Akt. Furthermore, distinct PI3-kinase inhibitors completely abrogated the protective effect of Hsp27 expression on Akt activation, Bax inactivation, and cell survival. These data show that Hsp27 antagonizes Bax-mediated mitochondrial injury and apoptosis by promoting Akt activation via a PI3-kinase-dependent mechanism. [ABSTRACT FROM AUTHOR]

The BCL-2 homologue MCL-1 plays an important role in the regulation of cell fate by blocking apoptosis as well as regulating cell cycle. MCL-1 has an unusual N-terminal extension, which contains a PEST domain and several phosphorylation sites that have been suggested to regulate its turnover. Here we report that the first 79 amino acids of MCL-1 regulate its subcellular localization. Deletion of this domain impairs both its mitochondrial localization and its anti-apoptotic activity. Conversely, expression of the N terminus of MCL-1 promotes both the association of MCL-1 with mitochondria and cell survival in a fashion that is dependent on the presence of endogenous MCL-1. In addition, the N terminus of MCL-1 has an antagonistic effect on proliferation. Although MCL-1 decreases proliferation through binding to proliferating cell nuclear antigen and cyclin-dependent kinase 1 in the nucleus, the N terminus of MCL-1 accelerates cell division. On the other hand, deletion of this region further increases the anti-proliferative activity of MCL-1. These results suggest that the N terminus of MCL-1 plays a major regulatory role, regulating coordinately the mitochondrial (anti-apoptotic) and nuclear (anti-proliferative) functions of MCL-1. [ABSTRACT FROM AUTHOR]

Propionyl.-L-carnitine (PLC) has been introduced among the therapeutic approaches of peripheral arterial disease, and more recently, an increase of intimal cell apoptosis has been demonstrated to contribute to its effectiveness in rabbit carotid postinjury myointimal hyperplasia prevention. How PLC mediates these effects on vascular smooth muscle cells (SMCs) remains poorly understood. We investigated the role of NF-κB in PLC-induced arterial remodeling. In vivo, daily PLC treatment 15 days after injury resulted in a reduction of relative rat aortic intimal volume, an increase of apoptosis, Bar up-regulation without changing the Bcl-2 level, and a reduction of NF-κB, vascular cell adhesion molecule-1, monocyte chemotactic protein-1, and survivin in myointimal thickening compared with controls. In the presence of 10% serum, a reduced G1 -→ S phase progression preceded PLC-induced intimal cell apoptosis; in 0.1% serum cultures, in a dose-dependent manner, PLC rapidly induced intimal cell apoptosis and reduced p65, p50, lAP-1, and IAP-2 expression. Inhibiting NF-κB activation through SN50 increased apoptotic rate and Bax expression in intimal but not in medial SMCs, and successive PLC treatment failed to induce a further increase in apoptotic rate. Bax antisense oligodeoxynucleotide reduced PLC-induced intimal cell apoptosis and cytochrome c release. The PLC-induced attenuation of NF-κB activity in intimal cells was also due to the increase of IκB-α bioavailability, as the result of a parallel induction of IκB-α synthesis and reduction of phosphorylation and degradation. Collectively, these findings document that NF-κB activity inhibition contributes to PLC-induced proliferative arrest and Bax-related apoptosis of intimal SMCs. [ABSTRACT FROM AUTHOR]

BAY 43-9006 is a kinase inhibitor that induces apoptosis in a variety of tumor cells. Here we report that treatment with BAY 43-9006 results in marked cytochrome c and AIF release into the cytosol, caspase-9, -8, -7, and -3 activation, and apoptosis in human leukemia cells (U937, Jurkat, and K562). Pronounced apoptosis was also observed in blasts from patients with acute myeloid leukemia. These events were accompanied by ERK1/2 inactivation and caspase-independent down-regulation of Mcl-1. Inducible expression of a constitutively active MEK1 construct did not prevent Mcl-1 down-regulation, suggesting that this event is not related to MEK/ERK pathway inactivation. Furthermore, BAY 43-9006 did not induce major changes in Mcl-1 mRNA levels monitored by real-time PCR or Mcl-1 promoter activity demonstrated by luciferase reporter assays, but it did enhance Mcl-1 down-regulation in actinomycin D-treated cells. Inhibition of protein synthesis by cycloheximide or proteasome function with MG132 and pulse-chase studies with [35S]methionine demonstrated that BAY 43–9006 did not diminish Mcl-1 protein stability, nor did it enhance Mcl-1 ubiquitination, but instead markedly attenuated Mcl-1 translation in association with the rapid and potent dephosphorylation of the elF4E translation initiation factor. Finally, ectopic expression of Mcl-1 in leukemic cells markedly inhibited BAY 43-9006-mediated cytochrome c cytosolic release, caspase-9, -7, and -3 activation, as well as cell death, indicating that Mcl-1 operates upstream of cytochrome c release and caspase activation. Together, these findings demonstrate that BAY 43-9006 mediates cell death in human leukemia cells, at least in part, through down-regulation of Mcl-1 via inhibition of translation. [ABSTRACT FROM AUTHOR]

Treatment with the protein kinase C activator 12-O-tetradecanoylphorbol 12-acetate (TPA) enables radiation-resistant LNCaP human prostate cancer cells to undergo radiation-induced apoptosis, mediated via activation of the enzyme ceramide synthase (CS) and de novo synthesis of the sphingolipid ceramide (Garzotto, M., Haimovitz­Friedman, A., Liao, W. C., White­Jones, M., Huryk, R, Heston, D. W. Wo, Cardon­Cardo, C., Kolesnick, R., and Fuks, Z. (1999) Cancer Res. 59, 5194–5201). Here, we show that TPA functions to decrease the cellular level of the ATM (ataxia telangiectasia mutated) protein, known to repress CS activation (Liao, W.-C., Haimovitz­ Friedman, A., Persaud, R., McLoughlin, M., Ehleiter, D., Zhang, N., Gatei, M., Lavin, M., Kolesnick, R., and Fuks, Z. (1999) J. Biol. Chem. 274, 17908–17917). Gel shift analysis in LNCaP and CWR22-Rv1 cells demonstrated a significant reduction in DNA binding of the Sp1 transcription factor to the ATM promoter, and quantitative reverse transcription-PCR showed a 50% reduction of ATM mRNA between 8 and 16 h of TPA treatment, indicating that TPA inhibits ATM transcription. Furthermore, treatment of LNCaP, CWR22-Rv1, PC-3, and DU-145 human prostate cells with antisense-ATM oligonucleotides, which markedly reduced cellular ATM levels, significantly enhanced radiation-induced CS activation and apoptosis, leading to apoptosis at doses as a low as 1 gray. These data suggest that the CS pathway initiates a generic mode of radiation-induced apoptosis in human prostate cancer cells, regulated by a suppressive function of ATM, and that ATM might represent a potential target for pharmacologic inactivation with potential clinical applications in human prostate cancer. [ABSTRACT FROM AUTHOR]

NAG-1 (nonsteroidal anti-inflammatory drug-activated gene), a member of the transforming growth factor β superfamily, is involved in cellular processes such as inflammation, apoptosis/survival, and tumorigenesis and is regulated by p53, Sp1, and Egr-1. In the current study, the regulation of NAG-1 expression in LNCaP human prostate carcinoma cells by 12-O-tetradecanoyl-phorbol-13-acetate (TPA) was examined. TPA treatment increased NAG-1 protein and mRNA levels in a time- and concentration-dependent manner as well as NF-κB binding/transcriptional activity in LNCaP cells. Pretreatment with protein kinase C (PKC) inhibitor blocked the TPA-induced increase in NAG-1 protein levels and NF-κB binding/transcriptional activity, whereas an inhibition of p38, JNK, MEK activity had no effect on TPA-induced NAG-1 levels and NF-κB transcriptional activity. Expression of constitutively active PKCs induced an increase in NF-κB transcriptional activity and NAG-1 protein levels in LNCaP cells. The expression of NF-κB p65 induced NAG-1 promoter activity, and chromatin immunoprecipitation assay for p65 showed that NF-κB binds the NAG-1 promoter in LNCaP cells. Inhibition of TPA-induced NAG-1 expression by NAG-1 short interfering RNA blocked TPA-induced apoptosis in LNCaP cells, suggesting induction of NAG-1 negatively affects LNCaP cell survival. These results demonstrate that NAG-1 expression is up-regulated by TPA in LNCaP cells through a PKC-dependent pathway involving the activation of NF-κB. [ABSTRACT FROM AUTHOR]