Endothelial cells, endoplasmic reticulum stress and oxysterols

Oxysterols are bioactive lipids that act as regulators of lipid metabolism, inflammation, cell viability and are involved in several diseases, including atherosclerosis. Mounting evidence linked the atherosclerosis to endothelium dysfunction; in fact, the endothelium regulates the vascular system with roles in processes such as hemostasis, cell cholesterol, hormone trafficking, signal transduction and inflammation. Several papers shed light the ability of oxysterols to induce apoptosis in different cell lines including endothelial cells. Apoptotic endothelial cell and endothelial denudation may constitute a critical step in the transition to plaque erosion and vessel thrombosis, so preventing the endothelial damaged has garnered considerable attention as a novel means of treating atherosclerosis. Endoplasmic reticulum (ER) is the site where the proteins are synthetized and folded and is necessary for most cellular activity; perturbations of ER homeostasis leads to a condition known as endoplasmic reticulum stress. This condition evokes the unfolded protein response (UPR) an adaptive pathway that aims to restore ER homeostasis. Mounting evidence suggests that chronic activation of UPR leads to cell dysfunction and death and recently has been implicated in pathogenesis of endothelial dysfunction. Autophagy is an essential catabolic mechanism that delivers misfolded proteins and damaged organelles to the lysosome for degradation, maintaining basal levels of autophagic activity it is critical for cell survival. Several evidence suggests that persistent ER stress often results in stimulation of autophagic activities, likely as a compensatory mechanism to relieve ER stress and consequently cell death. In this review, we summarize evidence for the effect of oxysterols on endothelial cells, especially focusing on oxysterols-mediated induction of endoplasmic reticulum stress

Proteomic changes and molecular effects associated with Cr(III) and Cr(VI) treatments on germinating kiwifruit pollen

The present study is aimed at identifying molecular changes elicited by Cr(III) and Cr(VI) on germinating kiwifruit pollen. To address this question, comparative proteomic and DNA laddering analyses were performed. While no genotoxic effect was detected, a number of proteins whose accumulation levels were altered by treatments were identified. In particular, the upregulation of some proteins involved in the scavenging response, cell redox homeostasis and lipid synthesis could be interpreted as an oxidative stress response induced by Cr treatment. The strong reduction of two proteins involved in mitochondrial oxidative phosphorylation and a decline in ATP levels were also observed. The decrease of pollen energy availability could be one of the causes of the severe inhibition of the pollen germination observed upon exposure to both Cr(III) and Cr(VI). Finally, proteomic and biochemical data indicate proteasome impairment: the consequential accumulation of misfolded/damaged proteins could be an important molecular mechanism of Cr(III) toxicity in pollen

Chromium toxicity to pollen, the male gametophyte of higher plants

The ability of both trivalent and hexavalent forms of chromium to interfere with some metabolic pathways in germinating kiwifruit pollen has been investigated. Chromium exposure resulted in a marked increase of ubiquitin-conjugated proteins, suggesting a role for the ubiquitin proteolytic system in the response to chromium stress. A significant rise of lipid peroxide production was also observed, more pronounced under Cr(VI)-treatment. GSH and GSSG content appeared to be affected by the metal, and both of them increased in the presence of each of the two chromium forms. In particular, Cr(III) induced a dose-dependent increase. Finally, dramatic alterations at the cell wall level of germinating kiwifruit pollen were induced by Cr(III). In fact, not only was the wall thickness highly irregular, but also the localization of arabinogalactan proteins, which are known to play an important role in cell wall assembly and expansion, was strongly altered as demonstrated by TEM-immunogold analysis by using JIM8 antibody. Key words: arabinogalactan proteins (AGPs), chromium, GSH/GSSG, kiwifruit, lipid peroxidation, pollen germination, ubiquiti

Overexpression of ubiquitin downregulates transcription of the endogenous UbC gene in HeLa cells

32nd FEBS Congressw, MOLECULAR MACHINE

Chromium toxicity to pollen, the male gametophyte of higher plants

The ability of both trivalent and hexavalent forms of chromium to interfere with some metabolic pathways in germinating kiwifruit pollen has been investigated. Chromium exposure resulted in a marked increase of ubiquitin-conjugated proteins, suggesting a role for the ubiquitin proteolytic system in the response to chromium stress. A significant rise of lipid peroxide production was also observed, more pronounced under Cr(VI)-treatment. GSH and GSSG content appeared to be affected by the metal, and both of them increased in the presence of each of the two chromium forms. In particular, Cr(III) induced a dose-dependent increase. Finally, dramatic alterations at the cell wall level of germinating kiwifruit pollen were induced by Cr(III). In fact, not only was the wall thickness highly irregular, but also the localization of arabinogalactan proteins, which are known to play an important role in cell wall assembly and expansion, was strongly altered as demonstrated by TEM-immunogold analysis by using JIM8 antibody. Key words: arabinogalactan proteins (AGPs), chromium, GSH/GSSG, kiwifruit, lipid peroxidation, pollen germination, ubiquiti

Ubiquitin in plant cells: focus on sexual reproduction processes

Si allega l'Introduction del libro, ad opera del Prof. V.K. Sawhney, University of Saskatchevan, Saskatoon, Canad

Induction of ubiquitin C (UBC) gene transcription is mediated by HSF1: role of proteotoxic and oxidative stress

The polyubiquitin gene ubiquitin C (UBC) is considered a stress protective gene and is upregulated under various stressful conditions, which is probably a consequence of an increased demand for ubiquitin in order to remove toxic misfolded proteins. We previously identified heat shock elements (HSEs) within the UBC promoter, which are responsible for heat shock factor (HSF)1-driven induction of the UBC gene and are activated by proteotoxic stress. Here, we determined the molecular players driving the UBC gene transcriptional response to arsenite treatment, mainly addressing the role of the nuclear factor-erythroid 2-related factor 2 (Nrf2)-mediated antioxidant pathway. Exposure of HeLa cells to arsenite caused a time-dependent increase of UBC mRNA, while cell viability and proteasome activity were not affected. Nuclear accumulation of HSF1 and Nrf2 transcription factors was detected upon both arsenite and MG132 treatment, while HSF2 nuclear levels increased in MG132-treated cells. Notably, siRNA-mediated knockdown of Nrf2 did not reduce UBC transcription under either basal or stressful conditions, but significantly impaired the constitutive and inducible expression of well-known antioxidant response element-dependent genes. A chromatin immunoprecipitation assay consistently failed to detect Nrf2 binding to the UBC promoter sequence. By contrast, depletion of HSF1, but not HSF2, significantly compromised stress-induced UBC expression. Critically, HSF1-mediated UBC trans-activation upon arsenite exposure relies on transcription factor binding to previously mapped distal HSEs, as demonstrated to occur under proteasome inhibition. These data highlight HSF1 as the pivotal transcription factor that translates different stress signals into UBC gene transcriptional induction