calpastatin and benzyloxycarbonylleucyl-leucyl-leucine-aldehyde

In HEK293 cells, exposure to various NAD(P)H oxidants, including phenazine methosulfate (PMS), that non-enzymatically oxidize intracellular NAD(P)H to NAD(P), decreased hypoxia-induced hypoxia-inducible factor 1 (HIF-1α) accumulation. RT-PCR and cycloheximide inhibition experiments indicated that PMS-induced HIF-1α decrease is involved in post-translational degradation during hypoxia. The decrease in HIF-1α caused by PMS was not eliminated by proteasome inhibitor MG132. Moreover, the increase in HIF-1α induced by exposure to MG132 alone in normoxia was diminished by PMS. In contrast, calpastatin peptide, a calpain inhibitor, fully prevented PMS-induced reduction in HIF-1α in hypoxic cells. These data suggest that the decreased stability of HIF-1α induced by PMS is due to the activation by PMS of a protein degradation system that is independent of the ubiquitin-proteasome pathway.

Topics: Calcium-Binding Proteins; Cell Hypoxia; Cycloheximide; Cysteine Proteinase Inhibitors; HEK293 Cells; Humans; Hypoxia-Inducible Factor 1, alpha Subunit; Leupeptins; Methylphenazonium Methosulfate; Oxidants; Oxygen; Proteasome Endopeptidase Complex; Proteasome Inhibitors; Protein Processing, Post-Translational; Protein Stability; Protein Synthesis Inhibitors; Proteolysis; Signal Transduction

Human cytomegalovirus (HCMV) stimulates arrested cells to enter the cell cycle by activating cyclin-dependent kinases (Cdks), notably Cdk2. Several mechanisms are involved in the activation of Cdk2. HCMV causes a substantial increase in the abundance of cyclin E and stimulates translocation of Cdk2 from the cytoplasm to the nucleus. Further, the abundance of the Cdk inhibitors (CKIs) p21cip1/waf1 (p21cip1) and p27kip1 is substantially reduced. The activity of cyclin E/Cdk2 increases as levels of CKIs, particularly p21cip1, fall. We have previously shown that these phenomena contribute to priming the cell for efficient replication of HCMV. In this study, the mechanisms responsible for the decrease in p21cip1 levels after HCMV infection were investigated by measuring p21cip1 RNA and protein levels in permissive human lung (LU) fibroblasts after HCMV infection. Northern blot analysis revealed that p21cip1 RNA levels increased briefly at 3 h after HCMV infection and then decreased to their nadir at 24 h; thereafter, RNA levels increased to about 60% of the preinfection level. Western blot analysis demonstrated that the relative abundance of p21cip1 protein roughly paralleled the observed changes in initial RNA levels; however, the final levels of protein were much lower than preinfection levels. After a transient increase at 3 h postinfection, p21cip1 abundance declined sharply over the next 24 h and remained at a very low level through 96 h postinfection. The disparity between p21cip1 RNA and protein levels suggested that the degradation of p21cip1 might be affected in HCMV-infected cells. Treatment of HCMV-infected cells with MG132, an inhibitor of proteasome-mediated proteolysis, provided substantial protection of p21cip1 in mock-infected cells, but MG132 was much less effective in protecting p21cip1 in HCMV-infected cells. The addition of E64d or Z-Leu-Leu-H, each an inhibitor of calpain activity, to HCMV-infected cells substantially increased the abundance of p21cip1 in a concentration-dependent manner. To verify that p21cip1 was a substrate for calpain, purified recombinant p21cip1 was incubated with either m-calpain or mu-calpain, which resulted in rapid proteolysis of p21cip1. E64d inhibited the proteolysis of p21cip1 catalyzed by either m-calpain or mu-calpain. Direct measurement of calpain activity in HCMV-infected LU cells indicated that HCMV infection induced a substantial and sustained increase in calpain activity, although there was no change in

Topics: Amino Acid Motifs; Calcium-Binding Proteins; Calpain; Cell Cycle; Cell Line; Cyclin-Dependent Kinase Inhibitor p21; Cyclins; Cysteine Endopeptidases; Cytomegalovirus; Dose-Response Relationship, Drug; Enzyme Activation; Humans; Leucine; Leupeptins; Multienzyme Complexes; Proteasome Endopeptidase Complex; RNA, Messenger; Time Factors; Ubiquitins

Both silica and lipopolysaccharide (LPS) induce a rapid degradation of I kappa B alpha, an intracellular inhibitor of the nuclear factor (NF)-kappa B transcription factor. In this report, we demonstrate that MG132, a relatively specific proteasome inhibitor, is capable of suppressing LPS-induced I kappa B alpha degradation and NF-kappa B activation in mouse macrophage line RAW 264.7 cells, but is unable to influence the same induction produced by silica. In contrast, the lysosome inhibitor chloroquine has little effect on I kappa B alpha degradation induced by either silica or LPS. In fact, chloroquine enhances the signal-induced nuclear expression of NF-kappa B p50/p65 heterodimer by inhibiting the resynthesis of I kappa B alpha. With the use of transient transfection of a plasmid that expresses calpastatin, a natural inhibitor for calpain, the silica-induced degradation of I kappa B alpha and NF-kappa B activation was attenuated. In contrast, no inhibition of LPS-induced I kappa B alpha degradation and NF-kappa B activation was observed by the overexpression of calpastatin. This suggests that calpain contributes to silica-induced I kappa B alpha degradation and NF-kappa B activation but not to LPS-induced I kappa B alpha degradation and NF-kappa B activation.

Topics: Animals; Blotting, Western; Calcium-Binding Proteins; Calpain; Cell Extracts; Cell Line; Chloroquine; Cysteine Proteinase Inhibitors; DNA-Binding Proteins; DNA, Complementary; I-kappa B Proteins; Leupeptins; Lipopolysaccharides; Macrophages; Mice; NF-kappa B; NF-KappaB Inhibitor alpha; Silicon Dioxide; Transfection