Activation of Nrf2 in defense against cadmium-induced oxidative stress.

Exposure to cadmium (Cd) elicits a range of adverse responses including oxidative damage and cancer. The molecular targets of Cd remain largely unidentified. Here, we analyzed the function and signal transduction of transcription factor Nrf2 in protection against Cd-induced oxidative stress. Wild-type (Nrf2 (+/+)) mouse embryonic fibroblasts (MEF) produced reactive oxygen species (ROS) at a low level, whereas treatment with Cd significantly increased the ROS production. On the other hand, Nrf2 knockout (Nrf2 (-/-)) MEF cells exhibited an elevated level of ROS under a basal condition, and Cd dramatically increased the ROS production at concentrations as low as 2 microM, resulting in increased sensitivity to Cd-induced cell death. Cd induced the basal and inducible expression of cytoprotective enzymes NQO1 and HO1 in WT MEF cells, but induction was lost in Nrf2 (-/-) MEF cells. Induction of the genes required antioxidant response elements (ARE) as Cd drove ARE-dependent reporter expression and Cd-activated Nrf2 bound to endogenous AREs in mouse hepa1c1c7 cells. Activation of Nrf2 by Cd involved stabilization of the Nrf2 protein, increased formation of Nrf2/Keap1 complex in the cytoplasm, translocation of the complex into the nucleus, and subsequently disruption of the complex. Lastly, Nrf2 was found ubiquitinated in the cytoplasm but deubiquitinated in the nucleus. The study provided a mechanistic transcriptional model in which Cd activates Nrf2 through a metal-activated signaling pathway involving a dynamic interplay between ubiquitination/deubiquitination and complex formation/dissociation of Nrf2 and Keap1.

Protection against chromium (VI)-induced oxidative stress and apoptosis by Nrf2. Recruiting Nrf2 into the nucleus and disrupting the nuclear Nrf2/Keap1 association.

Chromium (Cr) (VI) is a major environmental toxic metal and a human carcinogen. The molecular events mediating cellular responses to Cr(VI) are not clear at present. We show that Cr(VI) potently induced apoptosis and production of reactive oxygen species (ROS) in mouse hepa1c1c7 cells in a concentration-dependent manner. Mouse embryonic fibroblast cells lacking Nrf2 exhibited elevated ROS production and apoptosis, which were markedly further increased by Cr(VI), suggesting a protective role of Nrf2 against Cr(VI) toxicity. Protection by Nrf2 correlated with induction of cytoprotective genes Ho-1 and Nqo1. Induction of the genes by Cr(VI) involved inhibition of ubiquitination of Nrf2 and accumulation of Nrf2 into the nucleus. In the nucleus, treatment with Cr(VI), but not phenolic antioxidant tert-butylhydroquinone, librates Nrf2 from the Nrf2/Keap1 association and recruits Nrf2 to the antioxidant response elements (ARE) located in the enhancers of Ho-1 and Nqo1. Activation of Nrf2 by Cr(VI) was accompanied by the nuclear translocation and deubiquitination of Keap1 implicating recycling of Keap1 in Nrf2 signaling. Thus, protection against Cr(VI) toxicity involves a transcriptional signaling loop that includes activation of Nrf2 by the toxic metal, transcription of ARE-driven genes, and reduction of ROS production.

Arsenic induces NAD(P)H-quinone oxidoreductase I by disrupting the Nrf2 x Keap1 x Cul3 complex and recruiting Nrf2 x Maf to the antioxidant response element enhancer.

The ubiquitous toxic metalloid arsenic elicits pleiotropic adverse and adaptive responses in mammalian species. The biological targets of arsenic are largely unknown at present. We analyzed the signaling pathway for induction of detoxification gene NAD(P)H-quinone oxidoreductase (Nqo1) by arsenic. Genetic and biochemical evidence revealed that induction required cap 'n' collar basic leucine zipper transcription factor Nrf2 and the antioxidant response element (ARE) of Nqo1. Arsenic stabilized Nrf2 protein, extending the t(1/2) of Nrf2 from 21 to 200 min by inhibiting the Keap1 x Cul3-dependent ubiquitination and proteasomal turnover of Nrf2. Arsenic markedly inhibited the ubiquitination of Nrf2 but did not disrupt the Nrf2 x Keap1 x Cul3 association in the cytoplasm. In the nucleus, arsenic, but not phenolic antioxidant tert-butylhydroquinone, dissociated Nrf2 from Keap1 and Cul3 followed by dimerization of Nrf2 with a Maf protein (Maf G/Maf K). Chromatin immunoprecipitation demonstrated that Nrf2 and Maf associated with the endogenous Nqo1 ARE enhancer constitutively. Arsenic substantially increased the ARE occupancy by Nrf2 and Maf. In addition, Keap1 was shown to be ubiquitinated in the cytoplasm and deubiquitinated in the nucleus in the presence of arsenic without changing the protein level, implicating nuclear-cytoplasmic recycling of Keap1. Our data reveal that arsenic activates the Nrf2/Keap1 signaling pathway through a distinct mechanism from that by antioxidants and suggest an "on-switch" model of Nqo1 transcription in which the binding of Nrf2 x Maf to ARE controls both the basal and inducible expression of Nqo1.

Phase II trial of infusional cyclophosphamide, doxorubicin, and etoposide in patients with HIV-associated non-Hodgkin's lymphoma: an Eastern Cooperative Oncology Group Trial (E1494).

PURPOSE: To determine the effectiveness of an infusional chemotherapy regimen in patients with HIV-associated lymphoma treated before and after the use of highly active antiretroviral therapy (HAART) in routine clinical practice. PATIENTS AND METHODS: Ninety-eight assessable patients with HIV-associated intermediate- or high-grade non-Hodgkin's lymphoma received cyclophosphamide 200 mg/m(2)/d, doxorubicin 12.5 mg/m(2)/d, and etoposide 60 mg/m(2)/d (CDE) given by continuous intravenous infusion for 4 days (96 hours) every 4 weeks plus filgrastim. Concurrent antiretroviral treatment consisted of the nucleoside analog didanosine in the first 43 patients enrolled before December 1996 (pre-HAART group), or HAART in the remaining 55 patients enrolled after that time (HAART group). RESULTS: Complete response occurred in 44 patients (45%; 95% CI, 35% to 55%). Failure-free survival and overall survival (OS) at 2 years was 36% (95% CI, 26% to 46%) and 43% (95% CI, 33% to 53%), respectively. At the time of the analysis, 30% in the pre-HAART group were alive compared with 47% in the HAART group; when adjusted for varying length of follow-up, patients in the HAART group had improved OS (P =.039). Patients in the HAART group experienced less grade 4 nonhematologic toxicity (22% v 42%; P =.037), thrombocytopenia (31% v 52%; P =.033), and anemia (9% v 27%; P =.021), and had fewer treatment-associated deaths (0% v 10%; P =.013). CONCLUSION: Infusional CDE is an effective and potentially curative regimen for patients with HIV-associated lymphoma. Patients treated in the HAART era have less chemotherapy-associated toxicity and improved survival.

Stem cell transplantation for the management of primary systemic amyloidosis.

PURPOSE: To review the characteristics and outcomes of amyloidosis patients treated with high-dose chemotherapy and stem cell reconstitution. SUBJECTS AND METHODS: Sixty-six patients with biopsy-proven amyloidosis received transplants between March 1996 and January 2001. All patients had evidence of a clonal plasma cell dyscrasia; those with nonimmunoglobulin forms of amyloidosis were excluded, as were those who had no symptoms of amyloidosis, purpura, carpal tunnel syndrome, or symptomatic multiple myeloma. RESULTS: Amyloid was seen clinically in the kidneys (n = 45 patients), heart (n = 32), peripheral nerves (n = 11), and liver (n = 11). A monoclonal protein was found in the serum in 46 patients and in the urine in 57 patients. The median daily urinary protein loss was 4.1 g. Septal thickness, measured by echocardiography, ranged from 7 to 24 mm (median, 12 mm); 8 patients had a septal thickness > or =16 mm. Ten patients received transplants 1 year or more after diagnosis. All patients received melphalan-based chemotherapy; 17 patients were conditioned with total body irradiation. Nine patients required dialysis, 7 of whom died. Treatment-related mortality for stem cell transplantation was 14% (9/66). After a median of 25 months of follow-up after transplantation, the percentage of patients alive with one organ involved was 91% (31 of 34); two organs, 82% (18 of 22); three organs, 33% (3 of 9); and four organs, 0% (0 of 1). Hematologic responses were seen in 33 patients and organ responses in 32 patients. The 2-year actuarial survival of all patients was 70%. CONCLUSION: The number of organs involved before stem cell transplantation for amyloidosis is the most important factor in predicting subsequent survival. Stem cell transplantation should be considered as a treatment option for selected patients with amyloidosis.

Veno-occlusive disease of the liver after blood and marrow transplantation: analysis of pre- and post-transplant risk factors associated with severity and results of therapy with tissue plasminogen activator.

We reviewed our blood and marrow transplantation (BMT) database from April 1982 to July 1996 and identified 111 of 474 patients with serum bilirubin concentration (SBR) > or = 34 micromol/l for two consecutive days within the first 20 days after related allogeneic or autologous BMT. Of the 111, 73 fulfilled the Seattle criteria for veno-occlusive disease of the liver (VOD) and had no other obvious cause for liver dysfunction. The patients were 16-60 years old (median, 39 years), and 41 were male (56%). Fourteen patients (19%) had autologous BMT, and 59 (81%) had allogeneic BMT. Twenty-eight (38%), 12 (16%), and 33 (45%) patients had severe, moderate, and mild VOD, respectively, by Seattle criteria. None of 23 patients with maximum (max) SBR > or = 257 micromol/l survived, all patients with max SBR < or = 128 micromol/l survived, and 7 of 15 patients (47%) with max SBR 128-257 micromol/l survived. The only pre-transplantation risk factor predictive of severe VOD was advanced disease state (P = 0.035), and the only transplant factors that predicted severe VOD were max SBR (P = 0.01) and maximum blood urea level (P = 0.03). Ten patients (all with creatinine levels > or = 150 micromol/l) were treated with tissue plasminogen activator; only two had a significant response and only one survived beyond day 120.