Kejian Shi

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.

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.

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.

Sodium selenite-induced activation of DAPK promotes autophagy in human leukemia HL60 cells

Autophagy has been suggested as a possible mechanism for non-apoptotic death despite evidence from many species that autophagy represents a survival strategy of cells under stress. From our previous findings that supranutritional doses of sodium selenite induced apoptosis in human leukemia cells, now we show autophagic cell death occurred after selenite exposure in HL60, suggested an alternative mechanism for the potential therapeutic properties of selenite. Additionally, Death-associated Protein Kinase (DAPK) performed a significantly increased expression during this process, concomitantly with gradually decreased phosphorylation at Ser(308). We further reveal that the up-regulation of DAPK which depends on selenite-activated ERK had no effect on autophagy. However, activation of DAPK via PP2A-mediated dephosphorylation at Ser(308) serves as a new strategy for autophagy induction. In conclusion, these results indicate that PP2A-mediated activated DAPK sensitizes HL60 cells to selenite, ultimately triggers autophagic cell death pathway to commit cell demise.

Downregulation of protein kinase Cα was involved in selenite-induced apoptosis of NB4 cells.

We revealed in our previous research that sodium selenite induced obvious apoptosis of human leukemia NB4 cells, with reactive oxygen species (ROS), mitochondrial apoptosis pathway, and endoplasmic reticulum stress (ER stress) involved. In the present study, we revealed protein kinase Ca (PKCalpha) was dramatically downregulated in selenite-induced apoptosis, which was mediated by ROS. Besides, we confirmed PKCalpha played an antiapoptotic role through its effects on ERK1/2 and Akt, while its downregulation was attributed to caspase-3 and PP2Ac under the regulation of ROS. In summary, we speculated that in apoptosis of NB4 cells induced by selenite, PKCalpha functioned to counteract apoptosis, thus its downregulation seemed a mechanism aggravating apoptosis.

Selenite-induced autophagy antagonizes apoptosis in colorectal cancer cells in vitro and in vivo.

In the present study, we aimed to investigate the relationship between autophagy and apoptosis in selenite-treated colorectal cancer (CRC) cells. The effects of selenite on HCT116 and SW480 cell apoptosis were investigated with an Annexin V/propidium iodide (PI) double staining kit by flow cytometry. The punctate of LC3 protein following treatment with selenite was observed by a laser scanning confocal microscope and by transmission electron microscopy. Using western blot assays, we detected the apoptotic and autophagic markers in both CRC cells and mouse xenograft tumor models. We found that sodium selenite induced autophagy in the two CRC cell lines. Consistent with the in vitro results, we observed that the expression of autophagy marker LC3 was increased. Finally, we discovered that modulation of reactive oxygen species by MnTMPyP inhibited autophagy, while H2O2 activated autophagy. These results help to elucidate the anticancer effect of selenium, providing further evidence to exploit novel anticancer drugs targeting selenium.

Activation of p53 by sodium selenite switched human leukemia NB4 cells from autophagy to apoptosis.

It was revealed by our previous research that sodium selenite repressed autophagy accompanied by the induction of apoptosis in human leukemia NB4 cells. The inhibition of autophagy exerted a facilitative effect on apoptosis. In the present study, we further explored the mechanisms underlying the switch from autophagy to apoptosis and elucidated p53 played a key role. Selenite induced phosphorylation of p53 at the vital site Ser15 via p38MAPK and ERK. Subsequently p53 dissociated with its inhibitory protein mouse double minute 2 (MDM2). Meanwhile, the nucleolar protein B23 transferred from the nucleolus to the nucleoplasm and associated with MDM2, probably stabilizing p53. The active p53 participated in the decrease of autophagic protein Beclin-1 and LC-3, as well as activation of apoptosis-related caspases. Furthermore, in p53 mutant U937 leukemia cells, selenite could not elicit such a switch from autophagy to apoptosis, laying emphasis on the crucial role p53 played in this process.