Enzyme caspase

In some studies it has been shown that ITCs can cause increases in the pro-apoptotic caspase enzymes, caspase 3, caspase 8 or caspase However, in other work, specific caspase inhibitors failed to block cell death or cell detachment from the substratum . This suggests that caspase-activation may only be a bystander event, or may only occur after the initiating event of a block in the cell cycle. Indeed, although expression of c-Jun amino-terminal kinase (INK) in response to ITCs has been linked to the pro-apoptotic process, it remains entirely possible that this is a parallel signalling pathway, more closely related to the induction of Phase 1 or Phase 2 enzymes than to the... 

Apoptosis Programed or ordered cell death mediated by caspase enzymes... 

The strategy used by the cysteine proteases is most similar to that used by the chymotrypsin family. In these enzymes, a cysteine residue, activated by a histidine residue, plays the role of the nucleophile that attacks the peptide bond (see Figure 9.18). in a manner quite analogous to that of the serine residue in serine proteases. An ideal example of these proteins is papain, an enzyme purified from the fruit of the papaya. Mammalian proteases homologous to papain have been discovered, most notably the cathepsins, proteins having a role in the immune and other systems. The cysteine-based active site arose independently at least twice in the course of evolution the caspases, enzymes that play a major role in apoptosis (Section 2.4.3). have active sites similar to that of papain, but their overall structures are unrelated. 

Neurodegeneration is likely due in part to caspase enzyme driven apoptosis and drugs that inhibit the activation of caspase enzymes are being studied as a potential neuropro tec five sdategy. 

As ATP levels decrease, cellular calcium levels increase and activate a number of proteases, endonucleases, and other enzymes. Caspase enzymes also become activated. Caspase-3 rapidly cleaves PARP not bound to DNA, and to a lesser extent DNA-bound PARP. When PARP is cleaved, DNA is vulnerable to the actions of endonuclease, which is part of the apoptotic program. 

A unifying feature of all pro-apoptotic signal transduction pathways is their ability to relay a death stimulus to the caspases, enzymes responsible for the execution phase of apoptosis37. As noted previously, however, a caspase-independent mechanism of apoptosis has recently been proposed23. 

Caspases, a family of aspartate-specific cysteine proteases, are essential in the initiation and execution of apoptosis (Creagh et al., 2003 Cohen, 1997). They are expressed as inactive proenzymes (zymogens) that become active during apoptosis. Out of 14 caspase enzymes, caspase-3 appears to be the major effector of neuronal apoptosis induced by a variety of stimuli as well as traumatic injuries (Fig. 4.4). A role for caspase-3 in injury-induced neuronal cell death has been established using semispecific peptide caspase inhibitors. Caspases not only cleave other downstream caspases but also a variety of enzymes, cytokines, cytoskeletal, nuclear, and cell cycle regulatory proteins (Cohen, 1997). Their activities in brain and spinal cord tissues are regulated by the occurrence in zymogens form, by members of Bcl-2 family, and certain cellular inhibitor of apoptosis proteins (cIAPs). 

Apart from these two Vertex compounds, only one other caspase inhibitor, BDN-6556, has been used in clinical trials. This compound belongs to the class of oxamyl dipeptides and was originally developed by Idun Pharmaceuticals (taken over by Pfizer). It is the only pan-caspase inhibitor that has been evaluated in humans. BDN-6556 displays inhibitory activity against all tested human caspases. It is also an irreversible, caspase-specific inhibitor that does not inhibit other major classes of proteases, or other enzymes or receptors. The therapeutic potential of BDN-6556 was first evaluated in several animal models of liver disease because numerous publications suggested that apoptosis contributes substantially to the development of some hepatic diseases, such as alcoholic hepatitis, hepatitis B and C (HBV, HCV), non-alcoholic steato-hepatitis (NASH), and ischemia/reperfusion injury associated with liver transplant. Accordingly, BDN-6556 was tested in a phase I study. The drug was safe and... 

Also, phosphorylation of Akt results in activation of sterol regulatory-element binding protein 1 (SREBP1), a key transcription factor involved in regulation of lipogenic enzymes. In addition, some of the effects of insulin on cell proliferation and survival may be explained by an Akt-dependent inhibition of apoptosis through phosphorylation and inactivation of proa-poptotic proteins (e.g., BAD, Caspase 9). 

Guzikowski AP, Naleway JJ, Shipp CT, Schutte RC (2000) Synthesis of a macrocyclic rhodamine 110 enzyme substrate as an intracellular probe for caspase 3 activity. Tetrahedron Lett 41 4733 1735... 

Karvinen, J., Laitala, V., Makinen, M. L., Mulari, O., Tamminen, J., Hermonen, J., Hurskainen, P. and Hemmila, I. (2004). Fluorescence quenching-based assays for hydrolyzing enzymes. Application of time-resolved fluorometry in assays for caspase, helicase, and phosphatase. Anal. Chem. 76, 1429-1436. 

PARACEST agents with a response to enzymatic activity have also been reported. Pagel et al. used a Tm1 DOTA monoamide complex containing a peptide chain which is hydrolyzed by the Caspase-3 enzyme (204,205). Following enzymatic cleavage, the PARACEST effect originating from the amide proton disappears due to the hydrolysis of the amide bond. 

When upstream signaling transduction mechanisms contributing to DON-medi-ated apoptosis were investigated in cloned macrophages, specific inhibition of PKR and Hck additively suppressed DON-induced caspase-3 activity and apoptosis as well as p38, ERK, and JNK phosphorylation.59 Inhibition of PKR and Hck also inhibits DON-induced binding and enzyme activity of p53. 

N-Nitrosamines have been shown to be inhibitors of cysteine-containing enzymes. For example, dephostatin and other N-methyl-N-nitrosoanilines (1) were found to be inhibitors of the protein tyrosin phosphatases, papain and caspase [90,91]. Inhibition results from the S-nitrosation of the critical cysteine residues in the active sites of the enzymes by the nitrosamines. Compounds 6 and 7 have been found to inhibit thrombus formation in arterioles and venules of rats [92], while N-nitrosamide 9 exhibited vasodilation and mutagenicity as a result of NO release [93]. 

CASc Caspase, interleukin-1/3 converting enzyme (ICE) homologs E(M) 0(0) 3(3) 1BMQ... 

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