Role of lipid peroxidation in cellular responses to D,L-sulforaphane, a promising cancer chemopreventive agent.

D,L-sulforaphane (SFN), a synthetic analogue of the broccoli-derived l-isomer, is a highly promising cancer chemopreventive agent substantiated by inhibition of chemically induced cancer in rodents and prevention of cancer development and distant site metastasis in transgenic mouse models of cancer. SFN is also known to inhibit growth of human cancer cells in association with cell cycle arrest and reactive oxygen species-dependent apoptosis, but the mechanism of these cellular responses to SFN exposure is not fully understood. Because 4-hydroxynonenal (4-HNE), a product of lipid peroxidation (LPO), the formation of which is regulated by hGSTA1-1, assumes a pivotal role in oxidative stress-induced signal transduction, we investigated its contribution in growth arrest and apoptosis induction by SFN using HL60 and K562 human leukemic cell lines as a model. The SFN-induced formation of 4-HNE was suppressed in hGSTA1-1-overexpressing cells, which also acquired resistance to SFN-induced cytotoxicity, cell cycle arrest, and apoptosis. While resistance to SFN-induced cell cycle arrest by ectopic expression of hGSTA1-1 was associated with changes in levels of G2/M regulatory proteins, resistance to apoptosis correlated with an increased Bcl-xL/Bax ratio, inhibition of nuclear translocation of AIF, and attenuated cytochrome c release in cytosol. The hGSTA1-1-overexpressing cells exhibited enhanced cytoplasmic export of Daxx, nuclear accumulation of transcription factors Nrf2 and HSF1, and upregulation of their respective client proteins, gamma-GCS and HSP70. These findings not only reveal a central role of 4-HNE in cellular responses to SFN but also reaffirm that 4-HNE contributes to oxidative stress-mediated signaling.

Stem cells and neuroprotection: understanding the players.

The use of neuroprotective therapies begs the question of how such therapies could affect preexisting stem cell populations within the host, as well as those introduced through cell-replacement therapy. Multiple mechanisms may mediate stem cell responses to neuroprotectants such as host/donor age and gender, cellular lineage/differentiation status, and mitochondrial dynamics. Current therapeutic sources for stem cells are embryonic, somatic, or induced pluripotent, with very little known about the effects of gender, age, cell type, and mitochondrial dynamics. With the advent of therapies to stimulate and recruit endogenous stem cells or transplant donor cells into damage areas in the hopes of recuperative regeneration of lost neurons, it is important to discuss mechanisms that dictate the winning players in the neuroprotection game. This review will focus on our current understanding of the characteristics of renewing stem cells that may affect neuroprotection.

Estrogen actions on mitochondria--physiological and pathological implications.

Estrogens are potent neuroprotective hormones and mitochondria are the site of cellular life-death decisions. As such, it is not surprising that we and others have shown that estrogens have remarkable effects on mitochondrial function. Herein we provide evidence for a primary effect of estrogens on mitochondrial function, achieved in part by the import of estrogen receptor beta (ERbeta) into the mitochondria where it mediates a number of estrogen actions on this vital organelle. ERbeta is imported into the mitochondria, through tethering to cytosolic chaperone protein and/or through direct interaction with mitochondrial import proteins. In the mitochondria, ERbeta can affect transcription of critical mitochondrial genes through the interaction with estrogen response elements (ERE) or through protein-protein interactions with mitochondrially imported transcription factors. The potent effects of estrogens on mitochondrial function, particularly during mitochondrial stress, argues for a role of estrogens in the treatment of mitochondrial defects in chronic neurodegenerative diseases like Alzheimer's disease (AD) and Parkinson's disease (PD) and more acute conditions of mitochondrial compromise, like cerebral ischemia and traumatic brain injury.

4-Hydroxynonenal induces p53-mediated apoptosis in retinal pigment epithelial cells.

4-Hydroxynonenal (4-HNE) has been suggested to be involved in stress-induced signaling for apoptosis. In present studies, we have examined the effects of 4-HNE on the intrinsic apoptotic pathway associated with p53 in human retinal pigment epithelial (RPE and ARPE-19) cells. Our results show that 4-HNE causes induction, phosphorylation, and nuclear accumulation of p53 which is accompanied with down regulation of MDM2, activation of the pro-apoptotic p53 target genes viz. p21 and Bax, JNK, caspase3, and onset of apoptosis in treated RPE cells. Reduced expression of p53 by an efficient silencing of the p53 gene resulted in a significant resistance of these cells to 4-HNE-induced cell death. The effects of 4-HNE on the expression and functions of p53 are blocked in GSTA4-4 over expressing cells indicating that 4-HNE-induced, p53-mediated signaling for apoptosis is regulated by GSTs. Our results also show that the induction of p53 in tissues of mGsta4 (-/-) mice correlate with elevated levels of 4-HNE due to its impaired metabolism. Together, these studies suggest that 4-HNE is involved in p53-mediated signaling in in vitro cell cultures as well as in vivo that can be regulated by GSTs.

A peroxisome proliferator-activated receptor-gamma agonist and the p53 rescue drug CP-31398 inhibit the spontaneous immortalization of breast epithelial cells.

Cell immortalization is a critical and rate-limiting step in cancer progression. Agents that inhibit cell immortalization may have utility for novel molecular chemopreventive strategies. Preimmortal breast epithelial cells derived from a patient with the Li-Fraumeni Syndrome (LFS) can spontaneously immortalize in vitro at a measurable and reproducible frequency. In the present study, these cells were treated in vitro with low (nM) concentrations of potential and otherwise clinically validated chemopreventive agents, including several nonsteroidal anti-inflammatory drugs, rosiglitazone maleate, and the p53 rescue drug CP-31398. Rosiglitazone maleate (P < 0.05) and CP-31398 (P < 0.05) significantly inhibited the frequency of spontaneous immortalization of LFS breast epithelial cells compared with untreated controls. Nonsteroidal anti-inflammatory drugs, including specific cyclooxengenase-2 inhibitors, only moderately inhibited the spontaneous immortalization of preimmortal LFS breast epithelial cells. The significant effects of the p53 rescue drug CP-31398 correlated with the increase in cellular death induced by telomere shortening-induced DNA damage signals, including increases in p53 and p21 protein levels. Because immortalization is one step in cancer progression, these studies show the potential usefulness of a cell-based model system to screen the effects of known and potentially novel chemopreventive agents, using cell immortalization as an end point.

Characterization of growth and differentiation in a telomerase-immortalized human corneal epithelial cell line.

PURPOSE: To develop and characterize a telomerase-immortalized human corneal epithelial cell line (hTCEpi) to serve as an in vitro model for studying the molecular mechanisms involved in regulating human corneal epithelial cell differentiation. METHODS: Primary cultures of human corneal epithelial cells were infected with a retroviral vector encoding human telomerase reverse transcriptase (hTERT). Infected hTCEpi cells were selected, cloned, and characterized to identify telomerase activity, proliferative capacity, karyotype, and differentiative potential in routine culture and under consecutive submerged and air-lifted conditions. Cells were evaluated to measure cell cycle kinetics (anti-Ki-67, anti-p16), stratification (phalloidin and anti-ZO-1), and differentiation (anti-K3, anti-BCL-2 and TUNEL labeling). RESULTS: hTCEpi cells exhibited telomerase activity, a normal karyotype and cell cycle kinetics at greater than 240 population doublings, and loss of p16 after passage 10. Air-lifting produced a well stratified epithelium (five to seven cell layers) with apical ZO-1-stained tight junctions. Submersed culture demonstrated increasing expression of stratification markers (K5/K14) with K3-corneal keratin marker expression in long-term, air-lifted culture. Anti-BCL-2 staining showed both nuclear and cytoplasmic localization with loss of nuclear BCL-2 expression in TUNEL-labeled surface epithelial cells. CONCLUSIONS: hTCEpi cells stratify, differentiate, and desquamate similar to normal human corneal epithelium. Further study of the hTCEpi cell line may be valuable in studying the molecular mechanisms regulating corneal epithelial cell differentiation and desquamation.

4-ethoxymethylphenol: a novel phytoestrogen that acts as an agonist for human estrogen receptors.

Estrogen is the natural agonist of the estrogen receptor (ER). However, certain plant-derived compounds or phytoestrogens have been identified that mimic estrogens and act as agonists and/or antagonists of ERs, depending on subtype and target tissue. Using thin layer chromatography (TLC), gas chromatography-mass spectrometry (GC-MS), and proton nuclear magnetic resonance (1H-NMR), we identified a simple phenol, 4-ethoxymethylphenol (4EM), found in Maclura pomifera that acts as an agonist of ER-alpha and ER-beta in HeLa and MCF-7 cells. To study the effect of 4EM on ER-alpha and ER-beta activity, we performed transient transfection assays and showed that 4EM activated ER-dependent gene transcription in a dose-dependent manner on both ER subtypes and this activity was inhibited by trans-4-hydroxytamoxifen (4HT). Further, 4EM-mediated transcription in ER-alpha, like estrogen, was enhanced in the presence of coactivators, steroid receptor coactivator-1 (SRC-1), CREB binding proteins (CBP), and E6-associated protein (E6-AP). We found that 4EM was specific for ER and did not activate transcription of the progesterone receptor.