Adaptive responses to mTOR gene targeting in hematopoietic stem cells reveal a proliferative mechanism evasive to mTOR inhibition.

The mechanistic target of rapamycin (mTOR) is a central regulator of cell growth and an attractive anticancer target that integrates diverse signals to control cell proliferation. Previous studies using mTOR inhibitors have shown that mTOR targeting suppresses gene expression and cell proliferation. To date, however, mTOR-targeted therapies in cancer have seen limited efficacy, and one key issue is related to the development of evasive resistance. In this manuscript, through the use of a gene targeting mouse model, we have found that inducible deletion of mTOR in hematopoietic stem cells (HSCs) results in a loss of quiescence and increased proliferation. Adaptive to the mTOR loss, mTOR-/- HSCs increase chromatin accessibility and activate global gene expression, contrary to the effects of short-term inhibition by mTOR inhibitors. Mechanistically, such genomic changes are due to a rewiring and adaptive activation of the ERK/MNK/eIF4E signaling pathway that enhances the protein translation of RNA polymerase II, which in turn leads to increased c-Myc gene expression, allowing the HSCs to thrive despite the loss of a functional mTOR pathway. This adaptive mechanism can also be utilized by leukemia cells undergoing long-term mTOR inhibitor treatment to confer resistance to mTOR drug targeting. The resistance can be counteracted by MNK, CDK9, or c-Myc inhibition. These results provide insights into the physiological role of mTOR in mammalian stem cell regulation and implicate a mechanism of evasive resistance in the context of mTOR targeting.

Annexin II receptor induces apoptosis independent of Annexin II.

Annexin II receptor (AXIIR) is also known as chromosome 5 open reading frame 39 (C5orf39), it was originally identified as a cell surface receptor for Annexin II. AXIIR gene is peculiar to human. So far, the only known function about AXIIR is mediating Annexin II signal. In this study, we find that over-expression of AXIIR induces apoptosis, and this phenomenon is found in multiple human cell types. AXIIR is located in cytoplasm, binds to and activates pro-Caspase-8, which subsequently activates Caspase-3/7. AXIIR also down-regulates BCL2, BCL-XL, and activates Caspase-9, which finally activates Caspase-3/7 as well. Over-expression of BCL-XL does not affect AXIIR-induced apoptosis, whereas inhibition of Caspase-8 partially abolished AXIIR-induced apoptosis. AXIIR induces apoptosis independent of Annexin II and FADD. AXIIR is neither required for TRAIL-induced Caspase-8 activation. Although the transcriptional level of AXIIR in multiple cell types is considerably high, the translational level of AXIIR can hardly be detected. And inhibition of protein degradation pathways does not elevate AXIIR expression. Taken together, our observations reveal that besides being a cell surface receptor of Annexin II, AXIIR can also be located in cytoplasm and act as a novel inducer of apoptosis in human cells, partially through activating Caspase-8 in a manner that is different from conventional apoptotic pathways. The translation of AXIIR is generally tightly inhibited in cells. The physiological significance of such inhibition might be to prevent cells from apoptosis.

[Knockdown of proteasome subunit α7 with small interfering RNA inhibits cell proliferation of K562 cell line].

OBJECTIVE: To study the effect of human proteasome subunit Α7(PSMA7)gene silencing by small interfering RNA(siRNA)on human myeloid leukemia cell line K562. METHODS: PSMA7 gene-specific siRNA was chemically synthesized and transfected into K562 cell line by HiPerFect. The expression level of PSMA7 protein was detected by Western blot analysis. Cell proliferation was determined by MTS and cell counting. Cell cycle distribution was measured by flow cytometry. The expressions of Cyclin A, D, and E were detected by Western blot analysis. The apoptotic ratio was determined by flow cytometry. RESULTS: PSMA7 protein was evidently silenced 48 hours after transfection of the PSMA7-specific siRNA into K562 cell line. The proliferation of the cells was markedly inhibited, and the percentage of S phase cells decreased. However, no apoptosis was observed. The expressions of Cyclin A and E were down-regulated. CONCLUSION: Knockdown of PSMA7 down-regulates the expression of Cyclin A and E and thus decreases the proportion of cells in S phase as a result, the proliferation of K562 cell line is inhibited.

Kinase-independent role of mTOR and on-/off-target effects of an mTOR kinase inhibitor.

mTOR, as a serine/threonine kinase, is a widely pursued anticancer target. Multiple clinical trials of mTOR kinase inhibitors are ongoing, but their specificity and safety features remain lacking. Here, we have employed an inducible kinase-inactive D2338A mTOR knock-in mouse model (mTOR-/KI) together with a mTOR conditional knockout model (mTOR-/-) to assess the kinase-dependent/-independent function of mTOR in hematopoiesis and the on-/off-target effects of mTOR kinase inhibitor AZD2014. Despite exhibiting many similar phenotypes to mTOR-/- mice in hematopoiesis, the mTOR-/KI mice survived longer and showed differences in hematopoietic progenitor cells compared to mTOR-/- mice, suggesting a kinase-independent function of mTOR in hematopoiesis. Gene expression signatures in hematopoietic stem cells (HSCs) further revealed both kinase-dependent and independent effects of mTOR. AZD2014, a lead mTOR kinase inhibitor, appeared to work mostly on-target in suppressing mTOR kinase activity, mimicking that of mTOR-/KI HSCs in transcriptome analysis, but it also induced a small set of off-target responses in mTOR-/KI HSCs. In murine and human myeloid leukemia, besides kinase-inhibitory on-target effects, AZD2014 displayed similar off-target and growth-inhibitory cytostatic effects. These studies provide new insights into kinase-dependent/-independent effects of mTOR in hematopoiesis and present a genetic means for precisely assessing the specificity of mTOR kinase inhibitors.

Autism-associated chromatin remodeler CHD8 regulates erythroblast cytokinesis and fine-tunes the balance of Rho GTPase signaling.

CHD8 is an ATP-dependent chromatin-remodeling factor whose monoallelic mutation defines a subtype of autism spectrum disorders (ASDs). Previous work found that CHD8 is required for the maintenance of hematopoiesis by integrating ATM-P53-mediated survival of hematopoietic stem/progenitor cells (HSPCs). Here, by using Chd8F/FMx1-Cre combined with a Trp53F/F mouse model that suppresses apoptosis of Chd8-/- HSPCs, we identify CHD8 as an essential regulator of erythroid differentiation. Chd8-/-P53-/- mice exhibited severe anemia conforming to congenital dyserythropoietic anemia (CDA) phenotypes. Loss of CHD8 leads to drastically decreased numbers of orthochromatic erythroblasts and increased binucleated and multinucleated basophilic erythroblasts with a cytokinesis failure in erythroblasts. CHD8 binds directly to the gene bodies of multiple Rho GTPase signaling genes in erythroblasts, and loss of CHD8 results in their dysregulated expression, leading to decreased RhoA and increased Rac1 and Cdc42 activities. Our study shows that autism-associated CHD8 is essential for erythroblast cytokinesis.

Small interfering RNAs screened from random siRNA library direct neuronal differentiation.

Directed neuronal differentiation is crucial for development of cell therapy and investigation of neurogenesis. However, limited differentiation-inducing agents are available and most of current differentiation regimens are complicated. Here we carried out a combinatorial high-throughput screen with a random siRNA library on murine P19 cell differentiation toward neuronal lineage. Two siRNAs screened from the library were able to direct neuronal differentiation, determined by nestin, neurofilament-M and MAP-2 up-regulation. This is the first trial of a screening procedure for neuronal differentiation-directing agents arising from a random siRNA library and demonstrates that a random siRNA library can be considered as a new resource in efforts to seek new agents for directed differentiation. As the random siRNA library has a broad coverage for the entire genome, screening using random siRNA library can be expected to greatly augment the repertoire of siRNAs for directed differentiation.

Genetic variants and clinical significance of pediatric acute lymphoblastic leukemia.

BACKGROUND: Acute lymphoblastic leukemia (ALL), the most common childhood malignancy, is characterized by molecular aberrations. Recently, genetic profiling has been fully investigated on ALL; however, the interaction between its genetic alterations and clinical features is still unclear. Therefore, we investigated the effects of genetic variants on ALL phenotypes and clinical outcomes. METHODS: Targeted exome sequencing technology was used to detect molecular profiling of 140 Chinese pediatric patients with ALL. Correlation of genetic features and clinical outcomes was analyzed. RESULTS: T-cell ALL (T-ALL) patients had higher initial white blood cell (WBC) count (34.8×109/L), higher incidence of mediastinal mass (26.9%), more relapse (23.1%), and enriched NOTCH1 (23.1%), FBXW7 (23.1%) and PHF6 (11.5%) mutations. Among the 18 recurrently mutated genes, SETD2 and TP53 mutations occurred more in female patients (P=0.041), NOTCH1 and SETD2 mutants were with higher initial WBC counts (≥50×109/L) (P=0.047 and P=0.041), JAK1 mutants were with higher minimal residual disease (MRD) level both on day 19 and day 46 (day 19 MRD ≥1%, P=0.039; day 46 MRD ≥0.01%, P=0.031) after induction chemotherapy. Multivariate analysis revealed that initial WBC counts (≥50×109/L), MLLr, and TP53 mutations were independent risk factors for 3-year relapse free survival (RFS) in ALL. Furthermore, TP53 mutations, age (<1 year or ≥10 years), and MLLr were independently associated with adverse outcome in B-cell ALL (B-ALL). CONCLUSIONS: MLLr and TP53 mutations are powerful predictors for adverse outcome in pediatric B-ALL and ALL. Genetic profiling can contribute to the improvement of prognostication and management in ALL patients.

Autophagy is dispensable for Kmt2a/Mll-Mllt3/Af9 AML maintenance and anti-leukemic effect of chloroquine.

Recently, macroautophagy/autophagy has emerged as a promising target in various types of solid tumor treatment. However, the impact of autophagy on acute myeloid leukemia (AML) maintenance and the validity of autophagy as a viable target in AML therapy remain unclear. Here we show that Kmt2a/Mll-Mllt3/Af9 AML (MA9-AML) cells have high autophagy flux compared with normal bone marrow cells, but autophagy-specific targeting, either through Rb1cc1-disruption to abolish autophagy initiation, or via Atg5-disruption to prevent phagophore (the autophagosome precursor) membrane elongation, does not affect the growth or survival of MA9-AML cells, either in vitro or in vivo. Mechanistically, neither Atg5 nor Rb1cc1 disruption impairs endolysosome formation or survival signaling pathways. The autophagy inhibitor chloroquine shows autophagy-independent anti-leukemic effects in vitro but has no efficacy in vivo likely due to limited achievable drug efficacy in blood. Further, vesicular exocytosis appears to mediate chloroquine resistance in AML cells, and exocytotic inhibition significantly enhances the anti-leukemic effect of chloroquine. Thus, chloroquine can induce leukemia cell death in vitro in an autophagy-independent manner but with inadequate efficacy in vivo, and vesicular exocytosis is a possible mechanism of chloroquine resistance in MA9-AML. This study also reveals that autophagy-specific targeting is unlikely to benefit MA9-AML therapy.

[Cytogenetic characteristics of 163 children with acute lymphoblastic leukemia].

OBJECTIVE: To further understand the cytogenetic characteristics of pediatric acute lymphoblastic leukemia (ALL). METHODS: Cytogenetic abnormalities of 163 children with newly diagnosed ALL (0-17 years of age) were evaluated by conventional cytogenetic analysis and fluorescent in situ hybridization findings. RESULTS: Chromosome abnormalities were detected in 87.7% of patients (143/163). The ploidy levels most frequently observed among ALL patients were high hyperdiploidy (51-67 chromosomes) (45 cases, 27.6%), Chromosomes X and 21 were gained in 100% of these cases. The most common genetic alterations were t(12;21)/ETV6/RUNX1 (26 cases, 16.0%), followed by t(1;19)/TCF3/PBX1 (13 patients, 8.0%), t(4;11)/MLL rearrangement and t(8;14) IGH/MYC (6 cases, 3.7%), t(9;22)/BCR/ABL(2 cases, 1.2%), and iAMP21 (1 patient, 0.6%). The no-classical structural abnormalities included dup(1q) in 20.2%, del(6q) and del(9p) in 10.4%, del(12p) in 12.9% and del(13q) in 5.5%. The incidences of t(12;21), t(1;19), t(9;22) and high hyperdiploidy were consistent with reports in Western children (P>0.25). The incidence of (9;22) seemed to be much lower in our study than that in Korea (1.5% vs 9.5%, P<0.005). CONCLUSION: Cytogenetic findings of childhood ALL patients are similar to that of Western countries, it seems no more adverse risk factors.

Isolation of siRNA target by biotinylated siRNA reveals that human CCDC12 promotes early erythroid differentiation.

Erythroid differentiation is a tightly regulated multi-step process that has not been fully elucidated. We previously reported that a siRNA screened from random siRNA library, siRNA clone-67, induced erythroid differentiation in human erythroleukemia K-562cell line. Here we identified that human CCDC12 (coiled-coil domain containing 12) is a target of siRNA clone-67, by target capture with biotinylated siRNA. Over-expression of CCDC12 in K-562cell up-regulated the expression of CD235, ε-globin and γ-globin, accelerated cell growth, and slightly down-regulated the expression of GATA-2. Knockdown of CCDC12 slowed down the cell growth. These data indicate that CCDC12 is a new participant that promotes early erythroid differentiation.

Random small interfering RNA library screen identifies siRNAs that induce human erythroleukemia cell differentiation.

Cancers are characterized by poor differentiation. Differentiation therapy is a strategy to alleviate malignant phenotypes by inducing cancer cell differentiation. Here we carried out a combinatorial high-throughput screen with a random siRNA library on human erythroleukemia K-562 cell differentiation. Two siRNAs screened from the library were validated to be able to induce erythroid differentiation to varying degrees, determined by CD235 and globin up-regulation, GATA-2 down-regulation, and cell growth inhibition. The screen we performed here is the first trial of screening cancer differentiation-inducing agents from a random siRNA library, demonstrating that a random siRNA library can be considered as a new resource in efforts to seek new therapeutic agents for cancers. As a random siRNA library has a broad coverage for the entire genome, including known/unknown genes and protein coding/non-coding sequences, screening using a random siRNA library can be expected to greatly augment the repertoire of therapeutic siRNAs for cancers.