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Clive Dennison

Bio: Clive Dennison is an academic researcher from University of Natal. The author has contributed to research in topics: Cathepsin L & Cathepsin. The author has an hindex of 15, co-authored 34 publications receiving 1202 citations.

Papers
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TL;DR: The view is emerging that lysosomes are organelles for the storage of hydrolases, perhaps in an inactivated form, and such systems would permit simultaneous regulation of a number of unrelatedhydrolases.
Abstract: The endolysosomal system comprises a unique environment for proteolysis, which is regulated in a manner that apparently does not involve protease inhibitors. The system comprises a series of membrane-bound intracellular compartments, within which endocytosed material and redundant cellular components are hydrolysed. Endocytosed material tends to flow vectorially through the system, proceeding through the early endosome, the endosome carrier vesicle, the late endosome and the lysosome. Phagocytosis and autophagy provide alternative entry points into the system. Late endosomes, lysosome/late endosome hybrid organelles, phagosomes and autophagosomes are the principal sites for proteolysis. In each case, hydrolytic competence is due to components of the endolysosomal system, i.e. proteases, lysosome-associated membrane proteins, H(+)-ATPases and possibly cysteine transporters. The view is emerging that lysosomes are organelles for the storage of hydrolases, perhaps in an inactivated form. Once a substrate has entered a proteolytically competent environment, the rate-limiting proteolytic steps are probably effected by cysteine endoproteinases. As these are affected by pH and possibly redox potential, they may be regulated by the organelle luminal environment. Regulation is probably also affected, among other factors, by organelle fusion reactions, whereby the meeting of enzyme and substrate may be controlled. Such systems would permit simultaneous regulation of a number of unrelated hydrolases.

301 citations

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TL;DR: Electrostatic forces, and the tendency for salt ions to bind and tighten protein molecule conformation, are indicated by the sharp pH dependency of both conventional salting out and TPP, around pH regions where proteins undergo conformation changes.

292 citations

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TL;DR: Un certain nombre de proteines standards, ayant des proprietes physicochimiques connues, tels la BSA, le cytochrome C, the γ globuline, le lysozyme, l'ovalbumine, the myoglobine..., sont utilisees pour etudier le comportement de proteine dans un systeme triphasique de partage.
Abstract: Un certain nombre de proteines standards, ayant des proprietes physicochimiques connues, tels la BSA, le cytochrome C, la γ globuline, le lysozyme, l'ovalbumine, la myoglobine..., sont utilisees pour etudier le comportement de proteine dans un systeme triphasique de partage. Les effets de differents facteurs: pH, pI, temperature, concentration, masse moleculaire, ... intervenants dans la distribution de la proteine dans le systeme triphasique, sont etudies. Pour valider cette technique, une experience temoin utilisant les memes proteines standards est effectuee en electrophorese SDS-PAGE

114 citations

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TL;DR: The altered trafficking of cathepsins B and D may be of functional significance in malignant progression of human breast epithelial cells and in human breast carcinoma lines MCF-7 and BT20.
Abstract: Alterations in trafficking of cathepsins B and D have been reported in human and animal tumors. In MCF10 human breast epithelial cells, altered trafficking of cathepsin B occurs during their progression from a preneoplastic to neoplastic state. We now show that this is also the case for altered trafficking of cathepsin D. Nevertheless, the two cathepsins are not necessarily trafficked to the same vesicles. Perinuclear vesicles of immortal MCF10A cells label for both cathepsins B and D, yet the peripheral vesicles found in ras-transfected MCF10AneoT cells label for cathepsin B, cathepsin D or both enzymes. Studies at the electron microscopic level confirm these findings and show in addition surface labeling for both enzymes in the transfected cells. By immunofluorescence staining, cathepsin B can be localized on the outer surface of the cells. Similar patterns of peripheral intracellular and surface staining for cathepsin B are seen in the human breast carcinoma lines MCF7 and BT20. We suggest that the altered trafficking of cathepsins B and D may be of functional significance in malignant progression of human breast epithelial cells. Translocation of vesicles containing cathepsins B and D toward the cell periphery occurs in human breast epithelial cells that are at the point of transition between the pre-neoplastic and neoplastic state and remains part of the malignant phenotype of breast carcinoma cells.

82 citations

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TL;DR: The activity of cathepsin L is affected by ionic strength, resulting in the measured pH optimum being higher in acetate-4-morpholineethane sulfonic acid (MES)-Tris buffers of constant ionicstrength than in phosphate buffers of Constant molarity (and hence varying ionicStrength), which is differentially affected by the specific buffer ions.

67 citations


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TL;DR: It is shown that constitutive macroautophagy in primary cortical neurons is highly efficient, because newly formed autophagosomes are rapidly cleared by fusion with lysosomes, accounting for their scarcity in the healthy brain, and that the autophagic pathology observed in AD most likely arises from impaired clearance of AVs rather than strong autophagy induction alone.
Abstract: Macroautophagy, a major pathway for organelle and protein turnover, has been implicated in the neurodegeneration of Alzheimer's disease (AD). The basis for the profuse accumulation of autophagic vacuoles (AVs) in affected neurons of the AD brain, however, is unknown. In this study, we show that constitutive macroautophagy in primary cortical neurons is highly efficient, because newly formed autophagosomes are rapidly cleared by fusion with lysosomes, accounting for their scarcity in the healthy brain. Even after macroautophagy is strongly induced by suppressing mTOR (mammalian target of rapamycin) kinase activity with rapamycin or nutrient deprivation, active cathepsin-positive autolysosomes rather than LC3-II-positive autophagosomes predominate, implying efficient autophagosome clearance in healthy neurons. In contrast, selectively impeding late steps in macroautophagy by inhibiting cathepsin-mediated proteolysis within autolysosomes with cysteine- and aspartyl-protease inhibitors caused a marked accumulation of electron-dense double-membrane-limited AVs, containing cathepsin D and incompletely degraded LC3-II in perikarya and neurites. Similar structures accumulated in large numbers when fusion of autophagosomes with lysosomes was slowed by disrupting their transport on microtubules with vinblastine. Finally, we find that the autophagic vacuoles accumulating after protease inhibition or prolonged vinblastine treatment strongly resembled AVs that collect in dystrophic neurites in the AD brain and in an AD mouse model. We conclude that macroautophagy is constitutively active and highly efficient in healthy neurons and that the autophagic pathology observed in AD most likely arises from impaired clearance of AVs rather than strong autophagy induction alone. Therapeutic modulation of autophagy in AD may, therefore, require targeting late steps in the autophagic pathway.

1,001 citations

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TL;DR: An overview of the antimicrobial defences of the host cell is presented, with emphasis on macrophages, for which phagocytosis has been studied most extensively and some of the evasive strategies used by bacteria are described.
Abstract: Professional phagocytes have a vast and sophisticated arsenal of microbicidal features. They are capable of ingesting and destroying invading organisms, and can present microbial antigens on their surface, eliciting acquired immune responses. To survive this hostile response, certain bacterial species have developed evasive strategies that often involve the secretion of effectors to co-opt the cellular machinery of the host. In this Review, we present an overview of the antimicrobial defences of the host cell, with emphasis on macrophages, for which phagocytosis has been studied most extensively. In addition, using Mycobacterium tuberculosis, Listeria monocytogenes, Legionella pneumophila and Coxiella burnetii as examples, we describe some of the evasive strategies used by bacteria.

849 citations

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TL;DR: In early lactation, dietary CP and energy can profoundly affect milk yield, but current methods of assessing these nutrients are often inadequate to predict animal performance.

628 citations

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TL;DR: The effect of interactions among tumor cells, stromal cells, and the extracellular matrix on the regulation of protease expression is discussed and the role of inhibitors and novel protease-based drugs for clinical use are discussed.

598 citations

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TL;DR: In vitro study of the cellular uptake of peptides, originally deriving from protegrin (the SynB peptide vectors), that have also been shown to enhance the transport of drugs across the blood-brain barrier suggest that SynB and pAntp-(43–58) peptides penetrate into cells by an adsorptive-mediated endocytosis process rather than temperature-independent translocation.

549 citations