Caimin Xu

Sodium selenite induces apoptosis by ROS-mediated endoplasmic reticulum stress and mitochondrial dysfunction in human acute promyelocytic leukemia NB4 cells

IntroductionIn this study, we delineated the apoptotic signaling pathways activated by sodium selenite in NB4 cells.Materials and methodsNB4 cells were treated with 20 μM sodium selenite for different times. The activation of caspases and ER stress markers, ROS levels, mitochondrial membrane potential and cell apoptosis induced by sodium selenite were analyzed by immunoblotting analysis, DCF fluorescence and flow cytometric respectively. siRNA was used to detect the effect of GADD153 on selenite-induced cell apoptosis.ConclusionsSodium selenite-induced reactive oxygen species generation is an early event that triggers endoplasmic reticulum stress mitochondrial apoptotic pathways in NB4 cells.

Heat shock protein 90–mediated inactivation of nuclear factor-κB switches autophagy to apoptosis through becn1 transcriptional inhibition in selenite-induced NB4 cells

Here we report the novel function of heat shock protein 90 in regulating autophagy and apoptosis in human acute promyelocytic leukemia (APL)-derived NB4 cells, via decreased nuclear factor-κB activity and nucleus translocation, thus leading to down-regulation of autophagy-related component Beclin1. This study may be helpful in understanding the detail mechanism for sodium selenite in APL therapy.

ROS leads to MnSOD upregulation through ERK2 translocation and p53 activation in selenite‐induced apoptosis of NB4 cells

Following our previous finding that sodium selenite induces apoptosis in human leukemia NB4 cells, we now show that the expression of the critical antioxidant enzyme manganese superoxide dismutase (MnSOD) is remarkably elevated during this process. We further reveal that reactive oxygen species (ROS), especially superoxide radicals, play a crucial role in selenite‐induced MnSOD upregulation, with extracellular regulated kinase (ERK) and p53 closely implicated. Specifically, ERK2 translocates into the nucleus driven by ROS, where it directly phosphorylates p53, leading to dissociation of p53 from its inhibitory protein mouse double minute 2 (MDM2). Active p53 directly mediates the expression of MnSOD, serving as the link between ERK2 translocation and MnSOD upregulation.

The anticancer effects of sodium selenite and selenomethionine on human colorectal carcinoma cell lines in nude mice.

The studies were carried out on nude mice bearing human colorectal carcinoma SW480 cell line xenografts to evaluate the chemotherapeutic potential of selenium containing compounds such as sodium selenite (SSe) and selenomethionine (SeMet). Three doses of anticancer drugs were used, including 0.1 mg/kg/day SSe (LSSe), 2 mg/kg/day SSe (HSSe), and 2 mg/kg/day SeMet. We explored the anticancer effect of SSe and SeMet administered by IP injection for 21 days. We observed the pathologic changes and the cell apoptosis in tumor tissue by HE staining and TUNNEL assay after HSSe and SeMet treatment. GSH level and antioxidant enzyme GPX activity in tumor tissues were assessed. In addition, Western blotting was used to detect the expression of apoptosis-related proteins. The results suggested that HSSe and SeMet had significantly inhibited tumor growth in vivo. We also observed the pathologic changes and cell apoptosis in tumor tissues after HSSe and SeMet treatment. GSH level was a bit increased but the GPX activity was reduced. Moreover, SSe and SeMet treatment downregulated the expression of the protein Bcl-xL, increased the expression of Bax, Bad, and Bim, and activated caspase-9. SSe and SeMet may be the selective, low-toxic anticancer agents to treat human colorectal carcinoma cancer.

Selenite induces apoptosis in colorectal cancer cells via AKT-mediated inhibition of β-catenin survival axis

Mounting evidence reveals that selenium possesses chemotherapeutic potential against cancer cells. However, the molecular mechanisms underlying the anti-cancer effect of selenium remain elusive. In this study, with the aim to explore the detailed mechanisms how selenite induces apoptosis in colorectal cancer cells, we investigated the role of AKT/β-catenin signaling, a critical regulator of cell proliferation, survival and tumorigenesis, in selenite-induced apoptosis of colorectal cancer cells and xenograft tumors. We showed that selenite exerted a remarkable inhibitory effect on activation of AKT, leading to suppression of β-catenin activity and expression of its targets: cyclin D1 and survivin. Further experiments by transient expression of AKT and β-catenin revealed that inhibition of AKT/β-catenin was closely correlated with selenite-triggered apoptosis. Importantly, MnTMPyP pretreatment implied reactive oxygen species (ROS) was a crucial upstream signal for selenite-triggered inhibition of AKT/β-catenin. Overall, these observations demonstrate that selenite could induce apoptosis through ROS-dependent inhibition of AKT/β-catenin signaling in colorectal cancer cells in vitro and in vivo, and our findings yield novel insights into elucidating the mechanisms involved in the anti-cancer effect of selenium.

Exposure of human leukemia NB4 cells to increasing concentrations of selenite switches the signaling from pro-survival to pro-apoptosis

Selenium at low concentrations has a chemopreventive role against cancer, while at high concentrations, selenite exerts a direct antitumor effect. However, the mechanisms behind these effects remain elusive. In this study, we found that different concentrations of selenite triggered different signal pathways in human leukemia NB4 cells. Low concentrations of selenite elicited mild endoplasmic reticulum (ER) stress and mediated cell survival by activating unfolded protein response signaling, whereas high concentrations of selenite induced severe ER stress and caused cell death by activation of the pro-apoptotic transcription factors GADD153. In addition, selenite at low concentrations activated other anti-apoptotic pathways, such as AKT and ERK, whereas high concentrations of selenite induced activation of p53 and oxidative stress, which mediated the antitumor activity of selenite by causing mitochondrial dysfunction and caspase activation. These findings uncover the molecular mechanisms of the chemopreventive and antitumor effects of different concentrations of selenite.

ATF4 activation by the p38MAPK–eIF4E axis mediates apoptosis and autophagy induced by selenite in Jurkat cells

Previous studies have shown that selenite exerts pro‐apoptosis and pro‐autophagy effects and is associated with the activation of ER stress in T‐cell acute lymphoblastic leukemia (T‐ALL). Herein we demonstrate the underlying mechanisms by which the activation of p38MAPK plays essential roles in apoptosis and autophagy and the coordination of cellular metabolic processes during leukemia therapy. MKK3/6‐dependent activation of p38MAPK is required for the phosphorylation of eIF4E, thus initiating the translation of ER stress‐related transcription factor ATF4. Upregulated ATF4 results in the transcriptional initiation of the apoptosis‐related chop gene and autophagy‐related map1lc3b gene, through which selenite links ER stress to apoptosis and autophagy during leukemia treatment. Moreover, autophagy induction enhances cell apoptosis under this condition.

The p38 MAPK-regulated PKD1/CREB/Bcl-2 pathway contributes to selenite-induced colorectal cancer cell apoptosis in vitro and in vivo.

Supranutritional selenite has anti-cancer therapeutic effects in vivo; however, the detailed mechanisms underlying these effects are not clearly understood. Further studies would broaden our understanding of the anti-cancer effects of this compound and provide a theoretical basis for its clinical application. In this study, we primarily found that selenite exposure inhibited phosphorylation of cyclic adenosine monophosphate (cAMP)-response element binding protein (CREB), leading to suppression of Bcl-2 in HCT116 and SW480 colorectal cancer (CRC) cells. Moreover, the selenite-induced inhibitory effect on PKD1 activation was involved in suppression of the CREB signalling pathway. Additionally, we discovered that selenite treatment can upregulate p38 MAPK phosphorylation, which results in inhibition of the PKD1/CREB/Bcl-2 survival pathway and triggers apoptosis. Finally, we established a colorectal cancer xenograft model and found that selenite treatment markedly inhibits tumour growth through the MAPK/PKD1/CREB/Bcl-2 pathway in vivo. Our results demonstrated that a supranutritional dose of selenite induced CRC cell apoptosis through inhibition of the PKD1/CREB/Bcl-2 axis both in vitro and in vivo.

Sodium selenite alters microtubule assembly and induces apoptosis in vitro and in vivo

BackgroundPrevious studies demonstrated that selenite induced cancer-cell apoptosis through multiple mechanisms; however, effects of selenite on microtubules in leukemic cells have not been demonstrated.MethodsThe toxic effect of selenite on leukemic HL60 cells was performed with cell counting kit 8. Selenite effects on cell cycle distribution and apoptosis induction were determined by flow cytometry. The contents of cyclin B1, Mcl-1, AIF, cytochrome C, insoluble and soluble tubulins were detected with western blotting. Microtubules were visualized with indirect immunofluorescence microscopy. The interaction between CDK1 and Mcl-1 was assessed with immunoprecipitation. Decreasing Mcl-1 and cyclin B1 expression were carried out through siRNA interference. The alterations of Mcl-1 and cyclin B1 in animal model were detected with either immunohistochemical staining or western blotting. In situ detection of apoptotic ratio was performed with TUNEL assay.ResultsOur current results showed that selenite inhibited the growth of HL60 cells and induced mitochondrial-related apoptosis. Furthermore, we found that microtubule assembly in HL60 cells was altered, those cells were arrested at G2/M phase, and Cyclin B1 was up-regulated and interacted with CDK1, which led to down-regulation of the anti-apoptotic protein Mcl-1. Finally, in vivo experiments confirmed the in vitro microtubule disruption effect and alterations in Cyclin B1 and Mcl-1 levels by selenite.ConclusionsTaken together, the results from our study indicate that microtubules are novel targets of selenite in leukemic HL60 cells.

Comparative proteomic analysis of apoptosis induced by sodium selenite in human acute promyelocytic leukemia NB4 cells

Selenium (Se) is an essential trace element possessing anticarcinogenic properties. Sodium selenite (Na2SeO3) induced apoptosis in human acute promyelocytic leukemia (APL) cell line NB4 with dose and time dependency. In this study, proteomic techniques were used to study the apoptosis of NB4 cells induced by sodium selenite. Twenty‐six downregulated and four upregulated proteins were identified, which exhibited a 1.5‐fold change or greater. The identified proteins included key regulators of signal transduction such as Rho GDP dissociation inhibitor (Rho GDI) alpha and beta members of the MAPK family, and proteins involved in the regulation of c‐fos or c‐myc expression. Importantly, the identified proteins, hnRNP D0B and Rho GDI beta, which were related with the regulation of c‐myc, c‐fos, and c‐jun, were determined by reverse transcription‐polymerase chain reaction (RT‐PCR) to confirm their downregulation in proteomic study. Western blot analysis and RT‐PCR were then performed on three associated proteins: c‐Myc, c‐Fos, and c‐Jun, and their expression were observed to be significantly downregulated. Results showed that certain regulation involved in c‐myc, c‐fos, and c‐jun was present in the apoptosis, and the c‐Myc dependent‐on and Jun N‐terminal kinase (JNK) pathway also play roles. J. Cell. Biochem.