MG132

About: MG132 is a research topic. Over the lifetime, 1499 publications have been published within this topic receiving 56589 citations. The topic is also known as: MG132 & Z-Leu-leu-leu-al.

Angiotensin-(1–7) through AT2 receptors mediates tyrosine hydroxylase degradation via the ubiquitin–proteasome pathway

Abstract: Hypothalamic norepinephrine (NE) release regulates arterial pressure by altering sympathetic nervous system activity. Because angiotensin (Ang) (1-7) decreases hypothalamic NE release and this effect may be correlated with a diminished NE synthesis, we hypothesize that Ang-(1-7) down-regulates tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamines biosynthesis. We investigated the effect of Ang-(1-7) on centrally TH activity and expression. TH activity was evaluated by the release of tritiated water from (3)H-l-tyrosine. TH expression and phosphorylation were determined by western blot. Hypothalami from normotensive or spontaneously hypertensive rats pre-incubated with Ang-(1-7) showed a significant decrease in TH specific activity. Ang-(1-7) caused a decrease in TH phosphorylation at Ser19 and Ser40 residues. The heptapeptide induced a decrease in TH expression that was blocked by an AT(2) receptor antagonist and not by an AT(1) or Mas receptor antagonist, suggesting the involvement of AT(2) receptors. The proteasome inhibitor MG132 blocked the Ang-(1-7)-mediated TH reduction. In addition, Ang-(1-7) increased the amount of TH-ubiquitin complexes, indicating that the Ang-(1-7)-mediated TH degradation involves ubiquitin conjugation prior to proteasome degradation. We conclude that Ang-(1-7) down-regulates TH activity and expression centrally leading to a decrease in the central NE system activity.

Down-regulation of estrogen receptor-alpha and rearranged during transfection tyrosine kinase is associated with withaferin a-induced apoptosis in MCF-7 breast cancer cells

Abstract: Withaferin A (WA), a naturally occurring withanolide, induces apoptosis in both estrogen-responsive MCF-7 and estrogen-independent MDA-MB-231 breast cancer cell lines with higher sensitivity in MCF-7 cells, but the underlying mechanisms are not well defined. The purpose of this study was to determine the anti-cancer effects of WA in MCF-7 breast cancer cells and explore alterations in estrogen receptor alpha (ERα) and its associated molecules in vitro as novel mechanisms of WA action. The effects of WA on MCF-7 viability and proliferation were evaluated by 3-(4, 5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay and trypan blue exclusion assays. Apoptosis was evaluated by Annexin V-fluorescein isothiocyanate (FITC)/propidium iodide (PI) flow cytometry and Western blot analysis of poly (ADP-ribose) polymerase (PARP) cleavage. Cell cycle effects were analyzed by PI flow cytometry. Western blotting was also conducted to examine alterations in the expression of ERα and pathways that are associated with ERα function. WA resulted in growth inhibition and decreased viability in MCF-7 cells with an IC50 of 576 nM for 72 h. It also caused a dose- and time-dependent apoptosis and G2/M cell cycle arrest. WA-induced apoptosis was associated with down-regulation of ERα, REarranged during Transfection (RET) tyrosine kinase, and heat shock factor-1 (HSF1), as well as up-regulation of phosphorylated p38 mitogen-activated protein kinase (phospho-p38 MAPK), p53 and p21 protein expression. Co-treatment with protein synthesis inhibitor cycloheximide or proteasome inhibitor MG132 revealed that depletion of ERα by WA is post-translational, due to proteasome-dependent ERα degradation. Taken together, down-regulation of ERα, RET, HSF1 and up-regulation of phospho-p38 MAPK, p53, p21 are involved in the pro-apoptotic and growth-inhibitory effects of WA in MCF-7 breast cancer cells in vitro. Down-regulation of ERα protein levels by WA is caused by proteasome-dependent ERα degradation.

Proteasome inhibitors-mediated TRAIL resensitization and Bik accumulation.

Abstract: Proteasome inhibitors can resensitize cells that are resistant to tumors necrosis factor-related apoptotic-inducing ligand (TRAIL)-mediated apoptosis. However, the underlying mechanisms of this effect are unclear. To characterize the mechanisms of interaction between proteasome inhibitors and TRAIL protein, we evaluated the effects of combined treatment with the proteasome inhibitors bortezomib and MG132 and TRAIL protein on two TRAIL-resistant human colon cancer cell lines, DLD1-TRAIL/R and LOVO-TRAIL/R. Both bortezomib and MG132 in combination with TRAIL enhanced apoptotosis induction in these cells, as evidenced by enhanced cleavage of caspases 8, 9, and 3, Bid, poly (ADP-ribose) polymerase and by the release of cytochrome C and Smac. Subsequent studies showed that combined treatment with bortezomib or MG132 resulted in an increase of death receptor (DR) 5 and Bik at protein levels but had no effects on protein levels of DR4, Bax, Bak, Bcl-2, Bcl-XL, or Flice-inhibitory protein (FLIP). Moreover, c-Jun N-terminal kinase (JNK) is activated by these proteasome inhibitors. Blocking JNK activation with the JNK inhibitor SP600125 attenuated DR5 increase, but enhancement of apoptosis induction and increase of Bik protein were not affected. However, bortezomib-mediated TRAIL sensitization was partially blocked by using siRNA to knockdown Bik. Thus, our data suggests that accumulation of Bik may be critical for proteasome inhibitor-mediated re-sensitization of TRAIL.

Proteasome Inhibitors Induce p53/p21-Independent Apoptosis in Human Glioma Cells

Abstract: The proteasome is a multiprotein complex involved in the degradation of ubiquitinated proteins. Three proteasome inhibitors, calpain inhibitor I, lactacystin and MG132, induced apoptosis in several hu