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.

The effect of MG132, a proteasome inhibitor on HeLa cells in relation to cell growth, reactive oxygen species and GSH.

Abstract: MG132 (carbobenzoxy-Leu-Leu-leucinal) is a peptide aldehyde, which effectively blocks the proteolytic activity of the 26S proteasome complex. We evaluated the effects of MG132 on the growth of human cervix cancer HeLa cells in relation to the cell growth, reactive oxygen species (ROS) and glutathione (GSH) levels. Dose-dependent inhibition of cell growth was observed in HeLa cells with an IC50 of approximately 5 microM MG132 for 24 h. DNA flow cytometric analysis indicated that treatment with MG132 induced S, G2-M or non-specific phase arrests of the cell cycle dose-dependently. Treatment with MG132 induced apoptosis in a dose-dependent manner, as evidenced by sub-G1 cells and annexin V staining cells. Treatment with MG132 also induced the loss of mitochondrial membrane potential in HeLa cells. The intracellular ROS levels including O2*- were significantly increased in MG132-treated cells. Furthermore, the depletion of intracellular GSH content was observed in cells treated with MG132. In conclusion, MG132 inhibited the growth of HeLa cells via inducing the cell cycle arrest as well as triggering apoptosis. The changes of ROS and GSH by MG132 were closely related to apoptosis in HeLa cells.

Differential expression and stability of endogenous nuclear factor E2-related factor 2 (Nrf2) by natural chemopreventive compounds in HepG2 human hepatoma cells.

Abstract: Nuclear factor-E2-related factor 2 (Nrf2) is known as a key regulator of ARE-mediated gene expression and the induction of Phase II detoxifying enzymes and antioxidant enzymes, which is also a common property of many chemopreventive agents. In the present study, we investigated the regulatory role of different chemopreventive agents including sulforaphane (SUL), allyl isothiocyanate (AITC), indole-3-carbinol (I3C), and parthenolide (PTL), in the expression and degradation of Nrf2 and the induction of the antioxidant enzyme HO-1. SUL strongly induced Nrf2 protein expression and ARE-mediated transcription activation, retarded degradation of Nrf2 through inhibiting Keap1, and thereby activating the transcriptional expression of HO-1. AITC was also a potent inducer of Nrf2 protein expression, ARE-reporter gene and HO-1 but had little effect on delaying the degradation of Nrf2 protein. Although PTL and I3C could induce AREreporter gene expression and Nrf2 to some extent, they were not as potent as SUL and AITC. However, PTL dramatically induced the HO-1 expression, which was comparable to SUL, while I3C had no effect. In addition, when treated with SUL and PTL, inhibition of proteasome by MG132 did not cause additional accumulation of Nrf2, suggesting the involvement of other degradation mechanism(s) in the presence of these compounds such as SUL and PTL. In summary, the results of our current study indicated that different chemopreventive compounds have different regulatory properties on the accumulation and degradation of Nrf2 as well as the induction of cellular antioxidant enzyme HO-1.

CHIP and HSPs interact with β-APP in a proteasome-dependent manner and influence Aβ metabolism

Abstract: The C-terminus Hsp70 interacting protein (CHIP) has dual function as both co-chaperone and ubiquitin ligase. CHIP is increasingly implicated in the biology of polyglutamine expansion disorders, Parkinson's disease and tau protein in Alzheimer's disease. We investigated the involvement of CHIP in the metabolism of the beta-amyloid precursor protein and its derivative beta-amyloid (Abeta). Using immunoprecipitation, fluorescence localization and crosslinking methods, endogenous CHIP and betaAPP interact in brain and cultured skeletal myotubes as well as when they are expressed in stable HEK cell lines. Their interaction is confined to Golgi and ER compartments. In the presence of the proteasome inhibitor with MG132, endogenous and expressed betaAPP levels are significantly increased and accordingly, the interaction with CHIP enhanced. Concurrently, levels of Hsp70 were most consistently induced by proteasome inhibition among the various heat shock proteins (HSPs) tested. Thus, complexes of CHIP, Hsp70 and holo-betaAPP (as well as C-terminal fragments) were stabilized by the action of MG132. Moreover, CHIP itself is shown to both increase cellular holo-betaAPP levels and protect it from oxidative stress and degradation. Interestingly, CHIP also promotes the association of ubiquitin with betaAPP, implying that a smaller pool of betaAPP is destined for proteasomal processing. In neuronal cultures, CHIP and Hsp70/90 expression reduce steady-state cellular Abeta levels and hasten its degradation in pulse-chase experiments. The functional significance of CHIP and HSP interactions, especially with Hsp70, was tested using siRNA and in neuronal cells where protection from Abeta-induced toxicity is shown. We conclude that CHIP, as a bimolecular switch, interacts with HSP to stabilize normal holo-betaAPP on the one hand while also assisting in the ubiquitination of a subpopulation of betaAPP molecules that are destined for proteasome degradation. CHIP also hastens the clearance of Abeta in a manner consistent with its known neuroprotective properties.