Rapamycin inhibits pre-B acute lymphoblastic leukemia cells by downregulating DNA and RNA polymerases

Autophagy in Hematological Malignancies: Molecular Aspects in Leukemia and Lymphoma

The organization of the hematopoietic system is dependent on hematopoietic stem cells (HSCs) that are capable of self-renewal and multilineage differentiation to produce different blood cell lines. Autophagy has a central role in energy production and metabolism of the cells during starvation, cellular stress adaption, and removing mechanisms for aged or damaged organelles. The role and importance of autophagy pathways are becoming increasingly recognized in the literature because these pathways can be useful in organizing intracellular circulation, molecular complexes, and organelles to meet the needs of various hematopoietic cells. There is supporting evidence in the literature that autophagy plays an emerging role in the regulation of normal cells and that it also has important features in malignant hematopoiesis. Understanding the molecular details of the autophagy pathway can provide novel methods for more effective treatment of patients with leukemia. Overall, our review will emphasize the role of autophagy and its different aspects in hematological malignant neoplasms.

Autophagy-deficient mice are more susceptible to engrafted leukemogenesis

Autophagy is primarily considered as an important survival mechanism for both normal cells and cancer cells in response to metabolic stress or chemotherapy; but the role of autophagy in leukemogenesis is not fully understood. The aim of this study is to explore the role of intrinsic autophagy in the leukemogenesis of B-cell acute lymphoblastic leukemia (B-ALL). In this study, conditional knockout mice Atg7^f/f;Ubc-Cre, in which an autophagy-essential gene Atg7 is universally deleted, were used as recipients, B-ALL cell line 697 was used as donor cells to generate leukemia mouse model. Compared to wild-type mice, Atg7 knockout mice were more susceptible to engrafted leukemogenesis, shown by increase in white blood cells, lymphocytes, and platelets, decrease in HSPC number and its colony-forming unit (CFU). The liver and spleen displayed hepatosplenomegaly and inflammatory cell infiltration. Furthermore, second competitive transplantation revealed dysfunction of the HSPC in Atg7-knockout leukemia mice represented by destructive self-renew ability (CFU) and reconstitution ability including decreased B220, Ter 119 cells, and increased Gr-1 cell percentage. In summary, Mice with universal deletion of Atg7 are more inclined to the occurrence of engrafted human leukemia, which is largely attributed to the deterioration of the function of HSPC in autophagy deficient mice.

Therapeutic Modulation of Autophagy in Leukaemia and Lymphoma

Haematopoiesis is a tightly orchestrated process where a pool of hematopoietic stem and progenitor cells (HSPCs) with high self-renewal potential can give rise to both lymphoid and myeloid lineages. The HSPCs pool is reduced with ageing resulting in few HSPC clones maintaining haematopoiesis thereby reducing blood cell diversity, a phenomenon called clonal haematopoiesis. Clonal expansion of HSPCs carrying specific genetic mutations leads to increased risk for haematological malignancies. Therefore, it comes as no surprise that hematopoietic tumours develop in higher frequency in elderly people. Unfortunately, elderly patients with leukaemia or lymphoma still have an unsatisfactory prognosis compared to younger ones highlighting the need to develop more efficient therapies for this group of patients. Growing evidence indicates that macroautophagy (hereafter referred to as autophagy) is essential for health and longevity. This review is focusing on the role of autophagy in normal haematopoiesis as well as in leukaemia and lymphoma development. Attenuated autophagy may support early hematopoietic neoplasia whereas activation of autophagy in later stages of tumour development and in response to a variety of therapies rather triggers a pro-tumoral response. Novel insights into the role of autophagy in haematopoiesis will be discussed in light of designing new autophagy modulating therapies in hematopoietic cancers.

Abnormally high expression of POLD1, MCM2, and PLK4 promotes relapse of acute lymphoblastic leukemia

This study aimed to explore the underlying mechanism of relapsed acute lymphoblastic leukemia (ALL).Datasets of GSE28460 and GSE18497 were downloaded from Gene Expression Omnibus (GEO). Differentially expressed genes (DEGs) between diagnostic and relapsed ALL samples were identified using Limma package in R, and a Venn diagram was drawn. Next, functional enrichment analyses of co-regulated DEGs were performed. Based on the String database, protein-protein interaction network and module analyses were also conducted. Moreover, transcription factors and miRNAs targeting co-regulated DEGs were predicted using the WebGestalt online tool.A total of 71 co-regulated DEGs were identified, including 56 co-upregulated genes and 15 co-downregulated genes. Functional enrichment analyses showed that upregulated DEGs were significantly enriched in the cell cycle, and DNA replication, and repair related pathways. POLD1, MCM2, and PLK4 were hub proteins in both protein-protein interaction network and module, and might be potential targets of E2F. Additionally, POLD1 and MCM2 were found to be regulated by miR-520H via E2F1.High expression of POLD1, MCM2, and PLK4 might play positive roles in the recurrence of ALL, and could serve as potential therapeutic targets for the treatment of relapsed ALL.

[Rapamycin decreases irradiation-induced hematopoietic system damage]

目的

探讨雷帕霉素对⁶⁰Co辐照小鼠造血系统损伤的保护作用。

方法

6~8周龄C57BL/6J小鼠分为未辐照组与辐照组，每组再分为雷帕霉素预处理组和对照组。雷帕霉素预处理组小鼠给予雷帕霉素4 mg/kg，隔日腹腔注射，共5次，辐照组小鼠于末次注射后第2天接受⁶⁰Co全身照射(5 Gy)。辐照后第0.5、1、2、3、5、7、40、70天取外周血检测白细胞计数（WBC)、淋巴细胞计数（LYM)、红细胞计数（RBC)、血红蛋白含量（HGB）及血小板计数(PLT)，辐照后第5天观察小鼠胸骨骨髓有核细胞数量及内源性脾集落情况。

结果

①未辐照组：雷帕霉素预处理组WBC和LYM低于对照组(P值均<0.01），RBC和HGB高于对照组（P值均<0.05），PLT差异无统计学意义；两组小鼠骨髓有核细胞分布无差异。②辐照组：辐照后第0.5~7天雷帕霉素预处理组和对照组小鼠WBC、LYM均降低，两组比较差异无统计学意义，辐照后第40、70天均恢复，雷帕霉素预处理组均高于对照组(P<0.05)；辐照后第3~7天RBC和HGB均降低，但雷帕霉素预处理组均高于单独辐照组(P<0.05)，在辐照后第40、70天两组之间差异无统计学意义；PLT变化无明显规律。辐照后第5天，对照组小鼠骨髓有核细胞显著减少，但雷帕霉素预处理组有核细胞减少程度较对照组轻；雷帕霉素预处理组小鼠内源性脾集落数多于对照组（40.00±12.86对13.20±2.31，P=0.035）。

结论

雷帕霉素预处理可以减轻⁶⁰Co辐照引起的小鼠外周血细胞和骨髓有核细胞的减少，促进造血系统恢复，保护脾造血单位。

Autophagy Induction by Endothelial-Monocyte Activating Polypeptide II Contributes to the Inhibition of Malignant Biological Behaviors by the Combination of EMAP II with Rapamycin in Human Glioblastoma

This study aims to investigate the effect of endothelial-monocyte activating polypeptide II (EMAP II) on human glioblastoma (GBM) cells and glioblastoma stem cells (GSCs) as well as its possible mechanisms. In this study, EMAP II inhibited the cell viability and decreased the mitochondrial membrane potential in human GBM cells and GSCs, and autophagy inhibitor 3-methyl adenine (3-MA) blocked these effects. Autophagic vacuoles were formed in these cells after EMAP II treatment and this phenomenon was blocked by 3-MA. In addition, the up-regulation of microtubule-associated protein-1 light chain-3 (LC3)-II and the down-regulation of autophagic degraded substrate p62/SQSTM1 caused by EMAP II were observed. Cells treated with EMAP-II inhibited the PI3K/Akt/mTOR signal pathway, and PI3K/Akt agonist insulin-like growth factor-1 (IGF-1) blocked the effect of EMAP II on the expression of LC3-II and p62/SQSTM1. Cells exposed to EMAP-II experienced mitophagy and ER stress. Furthermore, the inhibition of cell proliferation, migration and invasion of GBM cells and GSCs were more remarkable by the combination of EMAP II and rapamycin than either agent alone in vitro and in vivo. The current study demonstrated that the cytotoxicity of EMAP II in human GBM cells and GSCs was induced by autophagy, accompanied by the inhibition of PI3K/Akt/mTOR signal pathway, mitophagy and ER stress. The combination of EMAP II with rapamycin demonstrated the inhibitory effect on the malignant biological behaviors of human GBM cells and GSCs in vitro and in vivo.

Autophagy collaborates with ubiquitination to downregulate oncoprotein E2A/Pbx1 in B-cell acute lymphoblastic leukemia

B-cell acute lymphoblastic leukemia (B-ALL) accounts for the most cancer incidences in children. We present here that autophagy is downregulated in pediatric B-ALL, suggesting a possible link between autophagy failure and pediatric B-ALL leukemogenesis. With a pediatric t(1;19) B-ALL xenograft mouse model, we show here that activation of autophagy by preventive administration of rapamycin improved the survival of leukemia animals by partial restoration of hematopoietic stem/progenitor cells, whereas treatment of the animals with rapamycin caused leukemia bone marrow cell-cycle arrest. Activation of autophagy in vitro or in vivo by rapamycin or starvation downregulated oncogenic fusion protein E2A/Pbx1. Furthermore, E2A/Pbx1 was found to be colocalized with autophagy marker LC3 in autolysosomes and with ubiquitin in response to autophagy stimuli, whereas autophagy or ubiquitination inhibitor blocked these colocalizations. Together, our data suggest a collaborative action between autophagy and ubiquitination in the degradation of E2A/Pbx1, thereby revealing a novel strategy for targeted preventive or treatment therapy on the pediatric ALL.