MDM2 Protein Overexpression Inhibits Apoptosis of TF-1 Granulocyte-Macrophage Colony-Stimulating Factor–Dependent Acute Myeloblastic Leukemia Cells

Antigen-Specific TCR-T Cells for Acute Myeloid Leukemia: State of the Art and Challenges

The cytogenetic abnormalities and molecular mutations involved in acute myeloid leukemia (AML) lead to unique treatment challenges. Although adoptive T-cell therapies (ACT) such as chimeric antigen receptor (CAR) T-cell therapy have shown promising results in the treatment of leukemias, especially B-cell malignancies, the optimal target surface antigen has yet to be discovered for AML. Alternatively, T-cell receptor (TCR)-redirected T cells can target intracellular antigens presented by HLA molecules, allowing the exploration of a broader territory of new therapeutic targets. Immunotherapy using adoptive transfer of WT1 antigen-specific TCR-T cells, for example, has had positive clinical successes in patients with AML. Nevertheless, AML can escape from immune system elimination by producing immunosuppressive factors or releasing several cytokines. This review presents recent advances of antigen-specific TCR-T cells in treating AML and discusses their challenges and future directions in clinical applications.

LC-MS/MS-based targeted proteomics quantitatively detects the interaction between p53 and MDM2 in breast cancer

In breast cancer, p53 could be functionally compromised by interaction with several proteins. Among those proteins, MDM2 serves as a pivotal negative regulator and counteracts p53 activation. Thus, the ability to quantitatively and accurately monitor the changes in level of p53-MDM2 interaction with disease state can enable an improved understanding of this protein-protein interaction (PPI), provide a better insight into cancer development and allow the emergence of advanced treatments. However, rare studies have evaluated the quantitative extent of PPI including p53-MDM2 interaction so far. In this study, a LC-MS/MS-based targeted proteomics assay was developed and coupled with co-immunoprecipitation (Co-IP) for the quantification of p53-MDM2 complex. A p53 antibody with the epitope residing at 156-214 residues achieved the greatest IP efficiency. 321KPLDGEYFTLQIR333 (p53) and 327ENWLPEDK334 (MDM2) were selected as surrogate peptides in the targeted analysis. Stable isotope-labeled synthetic peptides were used as internal standards. An LOQ (limit of quantification) of 2ng/mL was obtained. Then, the assay was applied to quantitatively detect total p53, total MDM2 and p53-MDM2 in breast cells and tissue samples. Western blotting was performed for a comparison. Finally, a quantitative time-course analysis in MCF-7 cells with the treatment of nutlin-3 as a PPI inhibitor was also monitored.

BIOLOGICAL SIGNIFICANCE

Proteins do not function as single entities but rather as a team player that has to communicate. Protein-protein interaction (PPI), normally by means of non-covalent contact among binary or large protein complex, is essential for many cellular processes including cancer progression. Thus, the ability to quantitatively and accurately monitor the changes in level of PPI with disease state can enable an improved understanding of PPI, provide a better insight into cancer development and allow the emergence of advanced treatments. However, rare studies have evaluated the quantitative extent of PPI so far. The major issue of current available approaches is the trade-off between sensitivity and specificity. Thus, techniques with the ability to quantify PPIs with both high sensitivity (low false-negative rate) and high specificity (low false-positive rate) are eagerly desired. Liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based targeted proteomics has shown its potential to study biomolecules because of its high sensitivity, high selectivity and wide dynamic range. In this study, we made an effort to develop a LC-MS/MS-based targeted proteomics assay for the quantitative detection of p53-MDM2 interaction in breast cells and tissue samples.

Modelling the onset of senescence at the G1/S cell cycle checkpoint

BACKGROUND

DNA damage (single or double-strand breaks) triggers adapted cellular responses. These responses are elicited through signalling pathways, which activate cell cycle checkpoints and basically lead to three cellular fates: cycle arrest promoting DNA repair, senescence (permanent arrest) or cell death. Cellular senescence is known for having a tumour-suppressive function and its regulation arouses a growing scientific interest. Here, we advance a qualitative model covering DNA damage response pathways, focusing on G1/S checkpoint enforcement, supposedly more sensitive to arrest than G2/M checkpoint.

RESULTS

We define a discrete, logical model encompassing ATM (ataxia telangiectasia mutated) and ATR (ATM and Rad3-related) pathways activation upon DNA damage, as well as G1/S checkpoint main components. It also includes the stress responsive protein p38MAPK (mitogen-activated protein kinase 14) known to be involved in the regulation of senescence. The model has four outcomes that convey alternative cell fates: proliferation, (transient) cell cycle arrest, apoptosis and senescence. Different levels of DNA damage are considered, defined by distinct combinations of single and double-strand breaks. Each leads to a single stable state denoting the cell fate adopted upon this specific damage. A range of model perturbations corresponding to gene loss-of-function or gain-of-function is compared to experimental mutations.

CONCLUSIONS

As a step towards an integrative model of DNA-damage response pathways to better cover the onset of senescence, our model focuses on G1/S checkpoint enforcement. This model qualitatively agrees with most experimental observations, including experiments involving mutations. Furthermore, it provides some predictions.

Dissecting the transcriptional phenotype of ribosomal protein deficiency: implications for Diamond-Blackfan Anemia

Defects in genes encoding ribosomal proteins cause Diamond Blackfan Anemia (DBA), a red cell aplasia often associated with physical abnormalities. Other bone marrow failure syndromes have been attributed to defects in ribosomal components but the link between erythropoiesis and the ribosome remains to be fully defined. Several lines of evidence suggest that defects in ribosome synthesis lead to “ribosomal stress” with p53 activation and either cell cycle arrest or induction of apoptosis. Pathways independent of p53 have also been proposed to play a role in DBA pathogenesis.

We took an unbiased approach to identify p53-independent pathways activated by defects in ribosome synthesis by analyzing global gene expression in various cellular models of DBA. Ranking-Principal Component Analysis (Ranking-PCA) was applied to the identified datasets to determine whether there are common sets of genes whose expression is altered in these different cellular models. We observed consistent changes in the expression of genes involved in cellular amino acid metabolic process, negative regulation of cell proliferation and cell redox homeostasis.

These data indicate that cells respond to defects in ribosome synthesis by changing the level of expression of a limited subset of genes involved in critical cellular processes. Moreover, our data support a role for p53-independent pathways in the pathophysiology of DBA.

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Ribosomopathies such as DBA are caused by ribosome dysfunction that activates p53.

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p53-independent pathways may suggest possible treatments for DBA.

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Expression analysis was performed in three p53-null models of DBA.

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Genes involved in apoptosis and cell redox homeostasis were especially affected.

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DBA is due to cumulative effects of p53-dependent and independent pathways.

PIM1 kinase is destabilized by ribosomal stress causing inhibition of cell cycle progression

PIM1 is a constitutively active serine/threonine kinase regulated by cytokines, growth factors and hormones. It has been implicated in the control of cell cycle progression and apoptosis and its overexpression has been associated with various kinds of lymphoid and hematopoietic malignancies. The activity of PIM1 is dependent on the phosphorylation of several targets involved in transcription, cell cycle and apoptosis. We have recently observed that PIM1 interacts with ribosomal protein (RP)S19 and cosediments with ribosomes. Defects in ribosome synthesis (ribosomal stress) have been shown to activate a p53-dependent growth arrest response. To investigate if PIM1 could have a role in the response to ribosomal stress, we induced ribosome synthesis alterations in TF-1 and K562 erythroid cell lines. We found that RP deficiency, induced by RNA interference or treatment with inhibitor of nucleolar functions, causes a drastic destabilization of PIM1. The lower level of PIM1 induces an increase in the cell cycle inhibitor p27(Kip1) and blocks cell proliferation even in the absence of p53. Notably, restoring PIM1 level by transfection causes a recovery of cell growth. Our data indicate that PIM1 may act as a sensor for ribosomal stress independently of or in concert with the known p53-dependent mechanisms.

Granulocyte-macrophage colony-stimulating factor: inhibitor of tumor necrosis factor-induced apoptosis

Tumor necrosis factor (TNF) can induce proliferation as well as apoptosis in acute myeloid leukemia (AML)-derived cells. We have shown recently that these seemingly contradictory effects are based on the divergent capacities of the cells to produce granulocyte-macrophage colony-stimulating factor (GM-CSF) upon stimulation with TNF. Only those cells that produce GM-CSF survive the TNF attack and start growing. Here, we set out to elucidate the mechanisms of the antiapoptotic effect of GM-CSF. Protection from apoptosis was achieved by preincubating TF-1 cells with exogeneous GM-CSF. Cycloheximide prevented protection, indicating that GM-CSF might induce synthesis of antiapoptotic proteins. Regulation of protective genes was analyzed using cDNA expression arrays and the results were verified by Northern and Western blot analysis. This screen revealed the elevated expression of BCL-2, BCL-2A1, BAG-1 and TACE upon stimulation with GM-CSF. The major novelty of our study is that GM-CSF carries protective effects against TNF-induced apoptosis, not only against apoptosis induced by irradiation or cytokine-starvation. This protection requires de novo protein synthesis and is not-or at least not exclusively-the consequence of a direct crosstalk between the GM-CSF and TNF signaling pathways.

Clinical use of topoisomerase I inhibitors in anticancer treatment

The camptothecin analogs topotecan and irinotecan have shown to be among the most effective anticancer agents and, as S-phase specific agents, their antitumor effect is maximized when they are administered in protracted schedules. The documented activity as single agents in many adult and pediatric malignancies has been followed by their use in combination with other anticancer agents. These studies have shown promising results, and have placed topotecan and irinotecan in the first line treatment for some malignancies. However, studies to better determine the optimal schedules and sequence of combinations are needed.

Diphtheria toxin fused to human interleukin-3 is toxic to blasts from patients with myeloid leukemias

Leukemic blasts from patients with acute phase chronic myeloid leukemic and refractory acute myeloid leukemia are highly resistant to a number of cytotoxic drugs. To overcome multi-drug resistance, we engineered a diphtheria fusion protein by fusing human interleukin-3 (IL3) to a truncated form of diphtheria toxin (DT) with a (G4S)2 linker (L), expressed and purified the recombinant protein, and tested the cytotoxicity of the DTLIL3 molecule on human leukemias and normal progenitors. The DTLIL3 construct was more cytotoxic to interleukin-3 receptor (IL3R) bearing human myeloid leukemia cell lines than receptor-negative cell lines based on assays of cytotoxicity using thymidine incorporation, growth in semi-solid medium and induction of apoptosis. Exposure of mononuclear cells to 680 pM DTLIL3 for 48 h in culture reduced the number of cells capable of forming colonies in semi-solid medium (colony-forming units leukemia) > or =10-fold in 4/11 (36%) patients with myeloid acute phase chronic myeloid leukemia (CML) and 3/9 (33%) patients with acute myeloid leukemia (AML). Normal myeloid progenitors (colony-forming unit granulocyte-macrophage) from five different donors treated and assayed under identical conditions showed intermediate sensitivity with three- to five-fold reductions in colonies. The sensitivity to DTLIL3 of leukemic progenitors from a number of acute phase CML patients suggests that this agent could have therapeutic potential for some patients with this disease.

The relationship between angiogenesis and the immune response in carcinogenesis and the progression of malignant disease

Recent studies have demonstrated that angiogenesis and suppressed cell-mediated immunity (CMI) play a central role in the pathogenesis of malignant disease facilitating tumour growth, invasion and metastasis. In the majority of tumours, the malignant process is preceded by a pathological condition or exposure to an irritant which itself is associated with the induction of angiogenesis and/or suppressed CMI. These include: cigarette smoking, chronic bronchitis and lung cancer; chronic oesophagitis and oesophageal cancer; chronic viral infections such as human papilloma virus and ano-genital cancers, chronic hepatitis B and C and hepatocellular carcinoma, and Epstein-Barr virus (EBV) and lymphomas; chronic inflammatory conditions such as Crohn's disease and ulcerative colitis and colorectal cancer; asbestos exposure and mesothelioma and excessive sunlight exposure/sunburn and malignant melanoma. Chronic exposure to growth factors (insulin-like growth factor-I in acromegaly), mutations in tumour suppressor genes (TP53 in Li Fraumeni syndrome) and long-term exposure to immunosuppressive agents (cyclosporin A) may also give rise to similar environments and are associated with the development of a range of solid tumours. The increased blood supply would facilitate the development and proliferation of an abnormal clone or clones of cells arising as the result of: (a) an inherited genetic abnormality; and/or (b) acquired somatic mutations, the latter due to local production and/or enhanced delivery of carcinogens and mutagenic growth factors. With progressive detrimental mutations and growth-induced tumour hypoxia, the transformed cell, to a lesser or greater extent, may amplify the angiogenic process and CMI suppression, thereby facilitating further tumour growth and metastasis. There is accumulating evidence that long-term treatment with cyclo-oxygenase inhibitors (aspirin and indomethacin), cytokines such as interferon-alpha, anti-oestrogens (tamoxifen and raloxifene) and captopril significantly reduces the incidence of solid tumours such as breast and colorectal cancer. These agents are anti-angiogenic and, in the case of aspirin, indomethacin and interferon-alpha have proven immunomodulatory effects. Collectively these observations indicate that angiogenesis and suppressed CMI play a central role in the development and progression of malignant disease.