Systematic Dissection of the Metabolic-Apoptotic Interface in AML Reveals Heme Biosynthesis to Be a Regulator of Drug Sensitivity

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Differentiation agents increase the potential AraC therapy of AML by reactivating cell death pathways without enhancing ROS generation

Acute myeloid leukemia (AML) has a poor prognosis and requires new approaches for treatment. We have reported that a combination of vitamin D-based cell differentiation agents (doxercalciferol/carnosic acid [D2/CA]) added following the cytotoxic drug arabinocytosine (AraC) increases AML cell death (CD), a model for improved therapy of this disease. Because AraC-induced CD is known to involve reactive oxygen species (ROS) generation, here we investigated if the modulation of cellular REDOX status plays a role in the enhancement of cell death (ECD) by D2/CA. Using thiol antioxidants, such as N-acetyl cysteine (NAC), we found a significant inhibition of ECD, yet this occurred in the absence of any detectable change in cellular ROS levels. In contrast, NAC reduced the vitamin D receptor (VDR) abundance and its signaling of ECD. Importantly, VDR knockdown and NAC similarly inhibited ECD without producing an additive effect. Thus, the proposed post-AraC therapy may be compromised by agents that reduce VDR levels in AML blasts.     

Reactivating PP2A by FTY720 as a novel therapy for AML with C-KIT tyrosine kinase domain mutation

The tyrosine kinase domain (TKD) mutations of receptor tyrosine kinase C-KIT are associated with a poor prognosis in acute myeloid leukemia (AML). However, the underlying mechanisms are not fully understood. We found the activity of protein phosphatase 2A (PP2A), a human tumor suppressor whose dysfunction contributes to malignant cell behavior, was significantly decreased in AML subgroups harboring C-KIT/D816V and AML cell line Kasumi-1 bearing C-KIT/N822K mutation. Primary AML cells and various AML cell lines were treated with PP2A activator FTY720. FTY720 showed a toxic effect in all leukemic cells, especially for cells harboring C-KIT/TKD mutation. Furthermore, FTY720-induced toxicity in AML leukemic cells was mediated by restoration of PP2A activity, via down-regulation of PP2A inhibitor SET, dephosporylation of PP2A-C(TYR307), and up-regulation of relevant PP2A subunit A and B55α. Our research indicates that the decreased PP2A activity in AML harboring C-KIT/TKD mutation may make the restoration of PP2A activity a novel therapy for AML patients with C-KIT/TKD mutation.     

The role,mechanism and potentially therapeutic application of microRNA-29 family in acute myeloid leukemia

Abnormal proliferation, apoptosis repression and differentiation blockage of hematopoietic stem/progenitor cells have been characterized to be the main reasons leading to acute myeloid leukemia (AML). Previous studies showed that miR-29a and miR-29b could function as tumor suppressors in leukemogenesis. However, a comprehensive investigation of the function and mechanism of miR-29 family in AML development and their potentiality in AML therapy still need to be elucidated. Herein, we reported that the family members, miR-29a, -29b and -29c, were commonly downregulated in peripheral blood mononuclear cells and bone marrow (BM) CD34+ cells derived from AML patients as compared with the healthy donors. Overexpression of each miR-29 member in THP1 and NB4 cells markedly inhibited cell proliferation and promoted cell apoptosis. AKT2 and CCND2 mRNAs were demonstrated to be targets of the miR-29 members, and the role of miR-29 family was attributed to the decrease of Akt2 and CCND2, two key signaling molecules. Significantly increased Akt2, CCND2 and c-Myc levels in the AML cases were detected, which were correlated with the decreased miR-29 expression in AML blasts. Furthermore, a feed-back loop comprising of c-Myc, miR-29 family and Akt2 were found in myeloid leukemogenesis. Reintroduction of each miR-29 member partially corrected abnormal cell proliferation and apoptosis repression and myeloid differentiation arrest in AML BM blasts. An intravenous injection of miR-29a, -29b and -29c in the AML model mice relieved leukemic symptoms significantly. Taken together, our finding revealed a pivotal role of miR-29 family in AML development and rescue of miR-29 family expression in AML patients could provide a new therapeutic strategy.     

Functional proteomics of the epigenetic regulators ASXL1, ASXL2 and ASXL3: a convergence of proteomics and epigenetics for translational medicine

ASXL1, ASXL2 and ASXL3 are epigenetic scaffolds for BAP1, EZH2, NCOA1, nuclear receptors and WTIP. Here, functional proteomics of the ASXL family members are reviewed with emphasis on mutation spectra, the ASXM2 domain and the plant homeodomain (PHD) finger. Copy number gains of ASXL1 occur in chromosome 20q11.2 duplication syndrome and cervical cancer. Truncation mutations of ASXLs occur in autism, Bohring–Opitz and related syndromes, hematological malignancies and solid tumors, such as prostate cancer, breast cancer and high-grade glioma, which are gain- or loss-of-function mutations. The ASXM2 domain is a binding module for androgen receptor and estrogen receptor α, while the PHD finger is a ligand of WTIP LIM domains and a putative chromatin-binding module. Phylogenetic analyses of 139 human PHD fingers revealed that ASXL PHD fingers cluster with those of BPTF, DIDO, ING1, KDM5A (JARID1A), KMT2E (MLL5), PHF2, PHF8 and PHF23. The cell context-dependent epigenetic code of ASXLs should be deciphered to develop therapeutics for human diseases.     

Direct modulation of the outer mitochondrial membrane channel,voltage-dependent anion channel 1 (VDAC1) by cannabidiol: a novel mechanism for cannabinoid-induced cell death

Cannabidiol (CBD) is a non-psychoactive plant cannabinoid that inhibits cell proliferation and induces cell death of cancer cells and activated immune cells. It is not an agonist of the classical CB1/CB2 cannabinoid receptors and the mechanism by which it functions is unknown. Here, we studied the effects of CBD on various mitochondrial functions in BV-2 microglial cells. Our findings indicate that CBD treatment leads to a biphasic increase in intracellular calcium levels and to changes in mitochondrial function and morphology leading to cell death. Density gradient fractionation analysis by mass spectrometry and western blotting showed colocalization of CBD with protein markers of mitochondria. Single-channel recordings of the outer-mitochondrial membrane protein, the voltage-dependent anion channel 1 (VDAC1) functioning in cell energy, metabolic homeostasis and apoptosis revealed that CBD markedly decreases channel conductance. Finally, using microscale thermophoresis, we showed a direct interaction between purified fluorescently labeled VDAC1 and CBD. Thus, VDAC1 seems to serve as a novel mitochondrial target for CBD. The inhibition of VDAC1 by CBD may be responsible for the immunosuppressive and anticancer effects of CBD.     

The hypoxic peri-arteriolar glioma stem cell niche,an integrated concept of five types of niches in human glioblastoma

Glioblastoma is the most lethal primary brain tumor and poor survival of glioblastoma patients is attributed to the presence of glioma stem cells (GSCs). These therapy-resistant, quiescent and pluripotent cells reside in GSC niches, which are specific microenvironments that protect GSCs against radiotherapy and chemotherapy. We previously showed the existence of hypoxic peri-arteriolar GSC niches in glioblastoma tumor samples. However, other studies have described peri-vascular niches, peri-hypoxic niches, peri-immune niches and extracellular matrix niches of GSCs. The aim of this review was to critically evaluate the literature on these five different types of GSC niches. In the present review, we describe that the five niche types are not distinct from one another, but should be considered to be parts of one integral GSC niche model, the hypoxic peri-arteriolar GSC niche. Moreover, hypoxic peri-arteriolar GSC niches are structural and functional look-alikes of hematopoietic stem cell (HSC) niches in the bone marrow. GSCs are maintained in peri-arteriolar niches by the same receptor-ligand interactions as HSCs in bone marrow. Our concept should be rigidly tested in the near future and applied to develop therapies to expel and keep GSCs out of their protective niches to render them more vulnerable to standard therapies.     

Mutation and expression analysis of the IDH1, IDH2, DNMT3A, and MYD88 genes in colorectal cancer

Colorectal cancer (CRC) is one of the leading causes of death around the world. Its genetic mechanism was intensively investigated in the past decades with findings of a number of canonical oncogenes and tumor-suppressor genes such as APC, KRAS, and TP53. Recent genome-wide association and sequencing studies have identified a series of promising oncogenes including IDH1, IDH2, DNMT3A, and MYD88 in hematologic malignancies. However, whether these genes are involved in CRC remains unknown. In this study, we screened the hotspot mutations of these four genes in 305 CRC samples from Han Chinese by direct sequencing. mRNA expression levels of these genes were quantified by quantitative real-time PCR (RT-qPCR) in paired cancerous and paracancerous tissues. Association analyses between mRNA expression levels and different cancerous stages were performed. Except for one patient harboring IDH1 mutation p.I99M, we identified no previously reported hotspot mutations in colorectal cancer tissues. mRNA expression levels of IDH1, DNMT3A, and MYD88, but not IDH2, were significantly decreased in the cancerous tissues comparing with the paired paracancerous normal tissues. Taken together, the hotspot mutations of IDH1, IDH2, DNMT3A, and MYD88 gene were absent in CRC. Aberrant mRNA expression of IDH1, DNMT3A, and MYD88 gene might be actively involved in the development of CRC.