Novel role of thiadiazolidine derivatives in inducing cell death through Myc-Max, Akt, FKHR, and FasL pathway

5-hydroxytryptamine synthesized in the aorta-gonad-mesonephros regulates hematopoietic stem and progenitor cell survival

Lv et al. show that in mice, 5-HT can be synthesized in the aorta-gonad-mesonephros and acts as a novel endogenous regulator of hematopoietic stem and progenitor cell (HSPC) development. The promoting effect of 5-HT on the survival of HSPCs in the intraaortic hematopoietic cluster is mediated through Htr5a-AKT-Foxo1 signaling.

The in vitro or ex vivo production of transplantable hematopoietic stem cells (HSCs) holds great promise for the treatment of hematological diseases in the clinic. However, HSCs have not been produced from either embryonic or induced pluripotent stem cells. In this study, we report that 5-hydroxytryptamine (5-HT; also called serotonin) can enhance the generation of hematopoietic stem and progenitor cells (HSPCs) in vitro and is essential for the survival of HSPCs in vivo during embryogenesis. In tryptophan hydroxylase 2–deficient embryos, a decrease in 5-HT synthesized in the aorta-gonad-mesonephros leads to apoptosis of nascent HSPCs. Mechanistically, 5-HT inhibits the AKT-Foxo1 signaling cascade to protect the earliest HSPCs in intraaortic hematopoietic clusters from excessive apoptosis. Collectively, our results reveal an unexpected role of 5-HT in HSPC development and suggest that 5-HT signaling may be a potential therapeutic target for promoting HSPC survival.

A phthalide derivative isolated from endophytic fungi Pestalotiopsis photiniae induces G1 cell cycle arrest and apoptosis in human HeLa cells

MP [4-(3′,3′-dimethylallyloxy)-5-methyl-6-methoxyphthalide] was obtained from liquid culture of Pestalotiopsis photiniae isolated from the Chinese Podocarpaceae plant Podocarpus macrophyllus. MP significantly inhibited the proliferation of HeLa tumor cell lines. After treatment with MP, characteristic apoptotic features such as DNA fragmentation and chromatin condensation were observed in DAPI-stained HeLa cells. Flow cytometry showed that MP induced G1 cell cycle arrest and apoptosis in a dose-dependent manner. Western blotting and real-time reverse transcription-polymerase chain reaction were used to investigate protein and mRNA expression. MP caused significant cell cycle arrest by upregulating the cyclin-dependent kinase inhibitor p27^KIP1 protein and p21^CIP1 mRNA levels in HeLa cells. The expression of p73 protein was increased after treatment with various MP concentrations. mRNA expression of the cell cycle-related genes, p21^CIP1, p16^INK4a and Gadd45α, was significantly upregulated and mRNA levels demonstrated significantly increased translation of p73, JunB, FKHR, and Bim. The results indicate that MP may be a potential treatment for cervical cancer.

Involvement of post-transcriptional regulation of FOXO1 by HuR in 5-FU-induced apoptosis in breast cancer cells

The post-transcriptional control of specific mRNAs is a widespread mechanism of gene regulation, which contributes to numerous biological processes in a number of cell types. The Forkhead box O (FoxO) transcription factor FOXO1 is an important tumor suppressor involved in apoptosis, the cell cycle, DNA damage repair and oxidative stress. Bioinformatic prediction identified that the 3' untranslated region (UTR) of FOXO1 is enriched with binding motifs for the human ELAV/Hu protein (HuR), indicating that FOXO1 is a potential target of HuR. Luciferase reporter assays demonstrate that HuR specifically regulates FOXO1 expression through AU-rich elements (AREs) within the FOXO1 3' UTR. Immunoprecipitation studies confirmed that HuR associates with FOXO1 mRNA in MDA-MB-231 breast cancer cells and that HuR upregulates FOXO1 mRNA levels through increased mRNA stability. Using a HuR loss- and gain-of-function approach, we revealed that FOXO1 expression was correspondingly decreased or increased in MDA-MB-231 cells. Functional assays demonstrated that HuR and FOXO1 expression levels were markedly enhanced upon 5-fluorouracil (5-FU) stimulation in MDA-MB-231 cells. Knockdown of HuR apparently abrogated 5-FU-induced apoptosis detected by caspase-3 activities. Furthermore, in HuR knockdown cells, additional overexpression of FOXO1 moderately recovered 5-FU-induced apoptosis, which verified that HuR-modulated apoptosis upon 5-FU treatment was partially mediated by its post-transcriptional regulation of FOXO1. Therefore, modulating FOXO1 expression has been suggested to lead to the development of new therapeutic treatments for certain types of cancer.

Targeting the Fas/FasL signaling pathway in cancer therapy

INTRODUCTION

The Fas/FasL system plays a significant role in tumorigenesis. Research has shown that its impairment in cancer cells may lead to apoptosis resistance and contribute to tumor progression. Thus, the development of effective therapies targeting the Fas/FasL system may play an important role in the fight against cancer.

AREAS COVERED

In this review the recent literature on targeting the Fas/FasL system for therapeutic exploitation at different levels is reviewed. Promising pre-clinical approaches and various exceptions are highlighted. The potential of combined therapies is also explored, whereby tumor sensitivity to Fas-mediated apoptosis is restored, before an effective targeted therapy is employed.

EXPERT OPINION

The success of the Fas/FasL system targeting for therapeutics will require a better understanding of the alterations conferring resistance, in order to use the most appropriate sensitizing chemotherapeutic or radiotherapeutic agents in combination with effective targeted therapies.

Hippo/Mst1 stimulates transcription of the proapoptotic mediator NOXA in a FoxO1-dependent manner

The proapoptotic protein Noxa, a member of the BH3-only Bcl-2 protein family, can effectively induce apoptosis in cancer cells, although the relevant regulatory pathways have been obscure. Previous studies of the cytotoxic effects of α-tocopheryl succinate (α-TOS) on cancer cells identified a mechanism whereby α-TOS caused apoptosis requiring the Noxa-Bak axis. In the present study, ab initio analysis revealed a conserved FoxO-binding site (DBE; DAF-16 binding element) in the NOXA promoter, and specific affinity of FoxO proteins to this DBE was confirmed by fluorescence anisotropy. FoxO1 and FoxO3a proteins accumulated in the nucleus of α-TOS-treated cells, and the drug-induced specific FoxO1 association with the NOXA promoter and its activation were validated by chromatin immunoprecipitation. Using siRNA knockdown, a specific role for the FoxO1 protein in activating NOXA transcription in cancer cells was identified. Furthermore, the proapoptotic kinase Hippo/Mst1 was found to be strongly activated by α-TOS, and inhibiting Hippo/Mst1 by specific siRNA prevented phosphorylation of FoxO1 and its nuclear translocation, thereby reducing levels of NOXA transcription and apoptosis in cancer cells exposed to α-TOS. Thus, we have demonstrated that anticancer drugs, exemplified by α-TOS, induce apoptosis by a mechanism involving the Hippo/Mst1-FoxO1-Noxa pathway. We propose that activation of this pathway provides a new paradigm for developing targeted cancer treatments.