Altered myelopoiesis and the development of acute myeloid leukemia in transgenic mice overexpressing cyclin A1

G-CSF/GM-CSF-induced hematopoietic dysregulation in the progression of solid tumors

There are two types of abnormal hematopoiesis in solid tumor occurrence and treatment: pathological hematopoiesis, and myelosuppression induced by radiotherapy and chemotherapy. In this review, we primarily focus on the abnormal pathological hematopoietic differentiation in cancer induced by tumor-released granulocyte colony stimulating factor (G-CSF) and granulocyte-macrophage colony stimulating factor (GM-CSF). As key factors in hematopoietic development, G-CSF/GM-CSF are well-known facilitators of myelopoiesis and mobilization of hematopoietic stem cells (HSCs). In addition, these two cytokines can also promote or inhibit tumors, dependent on tumor type. In multiple cancer types, hematopoiesis is greatly enhanced and abnormal lineage differentiation is induced by these two cytokines. Here, dysregulated hematopoiesis induced by G-CSF/GM-CSF in solid tumors and its mechanism are summarized, and the prognostic value of G-CSF/GM-CSF-associated dysregulated hematopoiesis for tumor metastasis is also briefly highlighted.

Evaluation of cyclin A1-specific T cells as a potential treatment for acute myeloid leukemia

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the only curative option for relapsed or refractory acute myeloid leukemia (AML). However, more than half ultimately experience disease relapse that is associated with a dismal median survival of just 6 months, highlighting the need for novel therapies. In the current study we explore the therapeutic potential of targeting cyclin A1 (CCNA1), a cancer-testis antigen that is overexpressed in malignant blasts and leukemic stem cells. We demonstrate the immunogenicity of this antigen to native T cells, with >90% of donors screened mounting a specific response. The expanded cells were Th1 polarized, polyfunctional, and cytotoxic toward CCNA1+/HLA-matched tumor cell lines. Furthermore, these cells were exquisitely specific for CCNA1 and exhibited no reactivity against other cyclin family members, including CCNA2, which shares 56% homology with CCNA1 and is ubiquitously expressed in dividing cells. Lastly, the detection of CCNA1-specific T cells in AML patients post-HSCT was associated with prolonged disease remission, suggesting the protective potential of such endogenous cells. Taken together, our findings demonstrate the feasibility of targeting CCNA1 and the potential for therapeutic benefit associated with the adoptive transfer of reactive cells.

PTPN11 Knockdown Prevents Changes in the Expression of Genes Controlling Cell Cycle, Chemotherapy Resistance, and Oncogene-Induced Senescence in Human Thyroid Cells Overexpressing BRAF V600E Oncogenic Protein

The MAPK (RAS/BRAF/MEK/ERK) signaling pathway is a kinase cascade involved in the regulation of cell proliferation, differentiation, and survival in response to external stimuli. The V600E mutation in the BRAF gene has been detected in various tumors, resulting in a 500-fold increase in BRAF kinase activity. However, monotherapy with selective BRAF V600E inhibitors often leads to reactivation of MAPK signaling cascade and emergence of drug resistance. Therefore, new targets are being developed for the inhibition of components of the aberrantly activated cascade. It was recently discovered that resistance to BRAF V600E inhibitors may be associated with the activity of the tyrosine phosphatase SHP-2 encoded by the PTPN11 gene. In this paper, we analyzed transcriptional effects of PTPN11 gene knockdown and selective suppression of BRAF V600E in a model of thyroid follicular epithelium. We found that the siRNA-mediated knockdown of PTPN11 after vemurafenib treatment prevented an increase in the expression CCNA1 and NOTCH4 genes involved in the formation of drug resistance of tumors. On the other hand, downregulation of PTPN11 expression blocked the transcriptional activation of genes (p21, p15, p16, RB1, and IGFBP7) involved in cell cycle regulation and oncogene-induced senescence in response to BRAF V600E expression. Therefore, it can be assumed that SHP-2 participates not only in emergence of drug resistance in cancer cells, but also in oncogene-induced cell senescence.

Cancer testis antigen Cyclin A1 harbors several HLA-A*02:01-restricted T cell epitopes, which are presented and recognized in vivo

Cyclin A1 is a promising antigen for T cell therapy being selectively expressed in high-grade ovarian cancer (OC) and acute myeloid leukemia (AML) stem cells. For adoptive T cell therapy, a single epitope has to be selected, with high affinity to MHC class I and adequate processing and presentation by malignant cells to trigger full activation of specific T cells. In silico prediction with three algorithms indicated 13 peptides of Cyclin A1 9 to 11 amino acids of length to have high affinity to HLA-A*02:01. Ten of them proved to be affine in an HLA stabilization assay using TAP-deficient T2 cells. Their immunogenicity was assessed by repetitive stimulation of CD8⁺ T cells from two healthy donors with single-peptide-pulsed dendritic cells or monocytes. Intracellular cytokine staining quantified the enrichment of peptide-specific functional T cells. Seven peptides were immunogenic, three of them against both donors. Specific cell lines were cloned and used in killing assays to demonstrate recognition of endogenous Cyclin A1 in the HLA-A*02:01-positive AML cell line THP-1. Immunopeptidome analysis based on direct isolation of HLA-presented peptides by mass spectrometry of primary AML and OC samples identified four naturally presented epitopes of Cyclin A1. The immunopeptidome of HeLa cells transfected with Cyclin A1 and HLA-A*02:01 revealed six Cyclin A1-derived HLA ligands. Epitope p410–420 showed high affinity to HLA-A*02:01 and immunogenicity in both donors. It proved to be naturally presented on primary AML blast and provoked spontaneous functional response of T cells from treatment naïve OC and, therefore, warrants further development for clinical application.

DUX4 Suppresses MHC Class I to Promote Cancer Immune Evasion and Resistance to Checkpoint Blockade

Advances in cancer immunotherapies make it critical to identify genes that modulate antigen presentation and tumor-immune interactions. We report that DUX4, an early embryonic transcription factor that is normally silenced in somatic tissues, is re-expressed in diverse solid cancers. Both cis-acting inherited genetic variation and somatically acquired mutations in trans-acting repressors contribute to DUX4 re-expression in cancer. Although many DUX4 target genes encode self-antigens, DUX4-expressing cancers were paradoxically characterized by reduced markers of anti-tumor cytolytic activity and lower major histocompatibility complex (MHC) class I gene expression. We demonstrate that DUX4 expression blocks interferon-γ-mediated induction of MHC class I, implicating suppressed antigen presentation in DUX4-mediated immune evasion. Clinical data in metastatic melanoma confirmed that DUX4 expression was associated with significantly reduced progression-free and overall survival in response to anti-CTLA-4. Our results demonstrate that cancers can escape immune surveillance by reactivating a normal developmental pathway and identify a therapeutically relevant mechanism of cell-intrinsic immune evasion.

High expression of FLT3 is a risk factor in leukemia

Several studies have shown that internal tandem duplication (ITD) of FMS-like tyrosine kinase 3 (FLT3) can result in the failure of leukemia treatment and contribute to a poor prognosis. However, the role of the overexpression of FLT3 in leukemia remains to be fully elucidated. By mining public database, the present study first identified that the expression of FLT3 in leukemia was markedly higher, compared with that in other types of tumor and cell lines, indicating that FLT3 is important in leukemia. In leukemia, FLT3 was found to be significantly upregulated in acute myeloid leukemia and acute lymphoblastic leukemia, and a high expression of FLT3 contributed to reduced survival rates. By analyzing Gene Expression Omnibus and The Cancer Genome Atlas data, it was found that genetic alterations and modification of DNA methylation increased the expression of FLT3 in leukemia. FLT3-ITD and FLT3 tyrosine kinase domain point mutations increased the expression of FLT3 in four independent datasets. In addition, the status of FLT3 gene methylation was negatively correlated with the expression of FLT3, and haploinsufficiency of DNA methyltransferase 1 increased the expression of Flt3 in mouse leukemia cells. By analyzing the enrichment of differentially-expressed genes in chemical and genetic perturbation datasets, it was found that genes, which were upregulated in the FLT3 high expression group had myeloid lymphoid leukemia- and nucleophosmin 1-like signatures, indicating that the overexpression of FLT3 may use the same mechanism to promote leukemia. Collectively, the results of the present study showed that the overexpression of FLT3 is a potential risk factor in leukemia.

Cyclin A1 expression and paclitaxel resistance in human ovarian cancer cells

BACKGROUND

The development of intrinsic and acquired resistance to antineoplastic agents is a major obstacle to successful chemotherapy in ovarian cancers. Identification and characterisation of chemoresponse-associated biomarkers are of paramount importance for novel therapeutic development.

METHODS

Global RNA expression profiles were obtained by high-throughput microarray analysis. Cell cycle, proliferation rate, and paclitaxel sensitivity of ovarian cancer cells harbouring cyclin A1-inducible expression construct were compared with and without tetracycline induction, as well as when the cyclin A1 expression was suppressed by short inhibiting RNA (siRNA). Cellular senescence was evaluated by β-galactosidase activity staining.

RESULTS

Global RNA expression profiling and subsequent correlation studies of gene expression level and drug response has identified that elevated expression of cyclin A1 (CCNA1) was significantly associated with cellular resistance to paclitaxel, doxorubicin and 5-fluorouracil. The role of cyclin A1 in paclitaxel resistance was confirmed in ovarian cancer cells that harbour an inducible cyclin A1 expression construct, which showed reduced paclitaxel-mediated growth inhibition and apoptosis when cyclin A1 expression was induced, whereas downregulation of cyclin A1 expression in the same cell lines using cyclin A1-specific siRNAs sensitised the cells to paclitaxel toxicity. However, ovarian cancer cells with ectopic expression of cyclin A1 demonstrated slowdown of proliferation and senescence-associated β-galactosidase activity.

CONCLUSIONS

Our profiling and correlation studies have identified cyclin A1 as one chemoresistance-associated biomarker in ovarian cancer. The results of the characterisation studies suggest that cyclin A1 functions as an oncogene that controls proliferative and survival activities in tumourigenesis and chemoresistance of ovarian cancer.

Characterization of children with FLT3-ITD acute myeloid leukemia: a report from the AIEOP AML-2002 study group

Recurrent molecular markers have been routinely used in acute myeloid leukemia (AML) for risk assessment at diagnosis, whereas their post-induction monitoring still represents a debated issue. We evaluated the prognostic value and biological impact of minimal residual disease (MRD) and of the allelic ratio (AR) of FLT3-internal-tandem duplication (ITD) in childhood AML. We retrospectively screened 494 children with de novo AML for FLT3-ITD mutation, identifying 54 harboring the mutation; 51% of them presented high ITD-AR at diagnosis and had worse event-free survival (EFS, 19.2 versus 63.5% for low ITD-AR, <0.05). Forty-one percent of children with high levels of MRD after the 1st induction course, measured by a patient-specific real-time-PCR, had worse EFS (22.2 versus 59.4% in low-MRD patients, P<0.05). Next, we correlated these parameters with gene expression, showing that patients with high ITD-AR or persistent MRD had characteristic expression profiles with deregulated genes involved in methylation and acetylation. Moreover, patients with high CyclinA1 expression presented an unfavorable EFS (20.3 versus 51.2% in low CyclinA1 group, P<0.01). Our results suggest that ITD-AR levels and molecular MRD should be considered in planning clinical management of FLT3-ITD patients. Different transcriptional activation of epigenetic and oncogenic profiles may explain variability in outcome among these patients, for whom novel therapeutic approaches are desirable.

Cyclin A1 regulates the interactions between mouse haematopoietic stem and progenitor cells and their niches

It remains poorly understood how the haematopoietic stem/progenitor cells (HSPC) are attracted to their niches and the functional consequences of such interaction. In the present study, we show that the cell cycle regulator cyclin A1 in association with vascular endothelial growth factor receptor 1 (VEGFR1), is required for HSPC and their niches to maintain their function and proper interaction. In the absence of cyclin A1, the HSPC in the BM are increased in their frequency and display an increased migratory and homing ability. Concomitantly, the ability of the endosteal and central BM niche zones to attract and home the wild-type HSPC is significantly reduced in cyclin A1-null mice as compared to the wild-type controls. The impaired proliferation and homing of HSPC in the BM of cyclin A1-null mice are attributed to the increased density of microvessels in the endosteal and central BM niche zones, which is associated with the increased VEGFR1 expression. Thus, modulation of cyclin A1 and VEGFR1 in HSPC and their niches may provide new insights into therapeutic approaches.

A Limited Role for the Cell Cycle Regulator Cyclin A1 in Murine Leukemogenesis

The quest for novel therapeutic targets in acute myeloid leukemia (AML) is still ongoing. One of such targets, cyclin A1, was shown to be overexpressed in AML including AML stem cells. However, the function of cyclin A1 in AML is largely unknown, and the data on its impact on patients´ survival remain controversial. Therefore, we developed a transgenic mouse model of stem cell-directed inducible cyclin A1 overexpression and crossed these mice with PML-RARα-knockin mice, which develop an AML M3-like phenotype. To observe the effects of cyclin A1 loss-of-function, we also crossed PML-RARα-knockin mice to cyclin A1-knockout mice. Neither overexpression nor loss of cyclin A1 significantly altered leukemogenesis in PML-RARα-knockin mice. These findings imply that upregulation of cyclin A1 is not essential for leukemogenesis. Our data suggest that cyclin A1 does not represent a suitable target for AML therapy.

Cyclin A1 expression predicts progression in pT1 urothelial carcinoma of bladder: a tissue microarray study of 149 patients treated by transurethral resection

AIMS

To evaluate the immunoexpression of cyclin A1 in pT1 urothelial carcinomas of the bladder (UC) from a cohort of patients treated by transurethral resection of the bladder (TURB), to determine its value in predicting tumour recurrence, tumour progression, or systemic metastases.

METHODS AND RESULTS

Five tissue microarrays (TMAS) were constructed from representative paraffin blocks of high-grade pT1 UC from 149 consecutive patients. Cyclin A1 immunoexpression was evaluated as the percentage of tumour cells with positive nuclear staining estimated at each TMA spot. The cutoff for cyclin A1 positivity was set at 10% of cells. Outcome variables included tumour recurrence and tumour progression as the primary endpoints. Cyclin A1 positivity was associated with tumour progression but not with tumour recurrence or the presence of adjacent carcinoma in situ in the biopsy. Also, patients with pT1b at biopsy and cyclin A1 expression showed higher progression rates than patients with pT1a at biopsy and without cyclin A1 expression, respectively. Combining pT1 stage at biopsy and cyclin A1 expression more accurately predicted tumour progression than pT1 stage at biopsy alone and cyclin A1 expression alone.

CONCLUSIONS

Cyclin A1 immunoexpression is of potential utility in predicting disease progression in patients with pT1 UC.

Cyclin A1 modulates the expression of vascular endothelial growth factor and promotes hormone-dependent growth and angiogenesis of breast cancer

Alterations in cellular pathways related to both endocrine and vascular endothelial growth factors (VEGF) may contribute to breast cancer progression. Inhibition of the elevated levels of these pathways is associated with clinical benefits. However, molecular mechanisms by which endocrine-related pathways and VEGF signalling cooperatively promote breast cancer progression remain poorly understood. In the present study, we show that the A-type cyclin, cyclin A1, known for its important role in the initiation of leukemia and prostate cancer metastasis, is highly expressed in primary breast cancer specimens and metastatic lesions, in contrasting to its barely detectable expression in normal human breast tissues. There is a statistically significant correlation between cyclin A1 and VEGF expression in breast cancer specimens from two patient cohorts (p<0.01). Induction of cyclin A1 overexpression in breast cancer cell line MCF-7 results in an enhanced invasiveness and a concomitant increase in VEGF expression. In addition, there is a formation of protein–protein complexes between cyclin A1 and estrogen receptor ER-α cyclin A1 overexpression increases ER-α expression in MCF-7 and T47D cells. In mouse tumor xenograft models in which mice were implanted with MCF-7 cells that overexpressed cyclin A1 or control vector, cyclin A1 overexpression results in an increase in tumor growth and angiogenesis, which is coincident with an enhanced expression of VEGF, VEGFR1 and ER-α Our findings unravel a novel role for cyclin A1 in growth and progression of breast cancer, and suggest that multiple cellular pathways, including cell cycle regulators, angiogenesis and estrogen receptor signalling, may cooperatively contribute to breast cancer progression.

In Vivo RNAi screening identifies a leukemia-specific dependence on integrin beta 3 signaling

We used an in vivo small hairpin RNA (shRNA) screening approach to identify genes that are essential for MLL-AF9 acute myeloid leukemia (AML). We found that Integrin Beta 3 (Itgb3) is essential for murine leukemia cells in vivo and for human leukemia cells in xenotransplantation studies. In leukemia cells, Itgb3 knockdown impaired homing, downregulated LSC transcriptional programs, and induced differentiation via the intracellular kinase Syk. In contrast, loss of Itgb3 in normal hematopoietic stem and progenitor cells did not affect engraftment, reconstitution, or differentiation. Finally, using an Itgb3 knockout mouse model, we confirmed that Itgb3 is dispensable for normal hematopoiesis but is required for leukemogenesis. Our results establish the significance of the Itgb3 signaling pathway as a potential therapeutic target in AML.

Regulation of APC(Cdh1) E3 ligase activity by the Fbw7/cyclin E signaling axis contributes to the tumor suppressor function of Fbw7

Fbw7 and Cdh1 are substrate-recognition subunits of the SCF- and APC-type E3 ubiquitin ligases, respectively. There is emerging evidence suggesting that both Fbw7 and Cdh1 function as tumor suppressors by targeting oncoproteins for destruction. Loss of Fbw7, but not Cdh1, is frequently observed in various human tumors. However, it remains largely unknown how Fbw7 mechanistically functions as a tumor suppressor and whether there is a signaling crosstalk between Fbw7 and Cdh1. Here, we report that Fbw7-deficient cells not only display elevated expression levels of SCF(Fbw7) substrates, including cyclin E, but also have increased expression of various APC(Cdh1) substrates. We further defined cyclin E as the critical signaling link by which Fbw7 governs APC(Cdh1) activity, as depletion of cyclin E in Fbw7-deficient cells results in decreased expression of APC(Cdh1) substrates to levels comparable to those in wild-type (WT) cells. Conversely, ectopic expression of cyclin E recapitulates the aberrant APC(Cdh1) substrate expression observed in Fbw7-deficient cells. More importantly, 4A-Cdh1 that is resistant to Cdk2/cyclin E-mediated phosphorylation, but not WT-Cdh1, reversed the elevated expression of various APC(Cdh1) substrates in Fbw7-deficient cells. Overexpression of 4A-Cdh1 also resulted in retarded cell growth and decreased anchorage-independent colony formation. Altogether, we have identified a novel regulatory mechanism by which Fbw7 governs Cdh1 activity in a cyclin E-dependent manner. As a result, loss of Fbw7 can lead to aberrant increase in the expression of both SCF(Fbw7) and APC(Cdh1) substrates. Our study provides a better understanding of the tumor suppressor function of Fbw7, and suggests that Cdk2/cyclin E inhibitors could serve as effective therapeutic agents for treating Fbw7-deficient tumors.

Cyclin-A1 represents a new immunogenic targetable antigen expressed in acute myeloid leukemia stem cells with characteristics of a cancer-testis antigen

Targeted T-cell therapy is a potentially less toxic strategy than allogeneic stem cell transplantation for providing a cytotoxic antileukemic response to eliminate leukemic stem cells (LSCs) in acute myeloid leukemia (AML). However, this strategy requires identification of leukemia-associated antigens that are immunogenic and exhibit selective high expression in AML LSCs. Using microarray expression analysis of LSCs, hematopoietic cell subpopulations, and peripheral tissues to screen for candidate antigens, cyclin-A1 was identified as a candidate gene. Cyclin-A1 promotes cell proliferation and survival, has been shown to be leukemogenic in mice, is detected in LSCs of more than 50% of AML patients, and is minimally expressed in normal tissues with exception of testis. Using dendritic cells pulsed with a cyclin-A1 peptide library, we generated T cells against several cyclin-A1 oligopeptides. Two HLA A*0201-restricted epitopes were further characterized, and specific CD8 T-cell clones recognized both peptide-pulsed target cells and the HLA A*0201-positive AML line THP-1, which expresses cyclin-A1. Furthermore, cyclin-A1-specific CD8 T cells lysed primary AML cells. Thus, cyclin-A1 is the first prototypic leukemia-testis-antigen to be expressed in AML LSCs. The pro-oncogenic activity, high expression levels, and multitude of immunogenic epitopes make it a viable target for pursuing T cell-based therapy approaches.

The ubiquitin-specific protease USP2a enhances tumor progression by targeting cyclin A1 in bladder cancer

The deubiquitinating enzyme USP2a has shown oncogenic properties in many cancer types by impairing ubiquitination of FASN, MDM2, MDMX or Aurora A. Aberrant expression of USP2a has been linked to progression of human tumors, particularly prostate cancer. However, little is known about the role of USP2a or its mechanism of action in bladder cancer. Here, we provide evidence that USP2a is an oncoprotein in bladder cancer cells. Enforced expression of USP2a caused enhanced proliferation, invasion, migration and resistance to several chemotherapeutic reagents, while USP2a loss resulted in slower proliferation, greater chemosensitivity and reduced migratory/invasive capability compared with control cells. USP2a, but not a catalytically inactive mutant, enhanced proliferation in immortalized TRT-HU1 normal human bladder epithelial cells. USP2a bound to cyclin A1 and prevented cyclin A1 ubiquitination, leading to accumulation of cyclin A1 by a block in degradation. Enforced expression of wild type USP2a, but not an inactive USP2a mutant, resulted in cyclin A1 accumulation and increased cell proliferation. We conclude that USP2a impairs ubiquitination and stabilizes an important cell cycle regulator, cyclin A1, raising the possibility of USP2a targeting as a therapeutic strategy against bladder tumors in combination with chemotherapy.

SERPINB13 is a novel RUNX1 target gene

RUNX1 is a critical transcription factor during embryogenesis and neoplastic disease. To identify novel transcriptional targets of RUNX1 in the context of chromatin, we performed genome wide location analysis (ChIP-on-chip). Here we report that SERPINB13, a gene downregulated in head and neck cancers, is a novel RUNX1transcriptional target. RUNX1 binds the SERPINB13 promoter in chromatin to repress its transcription. Mutation of either RUNX1 binding site in the SERPINB13 promoter increased the activity of the promoter. Finally, overexpression of RUNX1 and concomitant decrease in SERPINB13 expression led to increased activity of cathepsin K, an enzyme inhibited by SERPINB13. These data demonstrate that RUNX1 is an important regulator of SERPINB13 and cathepsin K activity.

Inhibitor of cyclin-dependent kinase (CDK) interacting with cyclin A1 (INCA1) regulates proliferation and is repressed by oncogenic signaling

The cell cycle is driven by the kinase activity of cyclin·cyclin-dependent kinase (CDK) complexes, which is negatively regulated by CDK inhibitor proteins. Recently, we identified INCA1 as an interaction partner and a substrate of cyclin A1 in complex with CDK2. On a functional level, we identified a novel cyclin-binding site in the INCA1 protein. INCA1 inhibited CDK2 activity and cell proliferation. The inhibitory effects depended on the cyclin-interacting domain. Mitogenic and oncogenic signals suppressed INCA1 expression, whereas it was induced by cell cycle arrest. We established a deletional mouse model that showed increased CDK2 activity in spleen with altered spleen architecture in Inca1(-/-) mice. Inca1(-/-) embryonic fibroblasts showed an increase in the fraction of S-phase cells. Furthermore, blasts from acute lymphoid leukemia and acute myeloid leukemia patients expressed significantly reduced INCA1 levels highlighting its relevance for growth control in vivo. Taken together, this study identifies a novel CDK inhibitor with reduced expression in acute myeloid and lymphoid leukemia. The molecular events that control the cell cycle occur in a sequential process to ensure a tight regulation, which is important for the survival of a cell and includes the detection and repair of genetic damage and the prevention of uncontrolled cell division.

Function of the A-type cyclins during gametogenesis and early embryogenesis

The cyclins and their cyclin-dependent kinase partners, the Cdks, are the basic components of the machinery that regulates the passage of cells through the cell cycle. Among the cyclins, those known as the A-type cyclins are unique in that in somatic cells, they appear to function at two stages of the cell cycle, at the G1-S transition and again as the cells prepare to enter M-phase. Higher vertebrate organisms have two A-type cyclins, cyclin A1 and cyclin A2, both of which are expressed in the germ line and/or early embryo, following highly specialized patterns that suggest functions in both mitosis and meiosis. Insight into their in vivo functions has been obtained from gene targeting experiments in the mouse model. Loss of cyclin A1 results in disruption of spermatogenesis and male sterility due to cell arrest in the late diplotene stage of the meiotic cell cycle. In contrast, cyclin A2-deficiency is marked by early embryonic lethality; thus, understanding the function of cyclin A2 in the adult germ line awaits conditional mutagenesis or other approaches to knock down its expression.

Favorable prognostic impact of NPM1 mutations in older patients with cytogenetically normal de novo acute myeloid leukemia and associated gene- and microRNA-expression signatures: a Cancer and Leukemia Group B study

PURPOSE

To analyze the prognostic significance of NPM1 mutations, and the associated gene- and microRNA-expression signatures in older patients with de novo, cytogenetically normal acute myeloid leukemia (CN-AML) treated with intensive chemotherapy.

PATIENTS AND METHODS

One hundred forty-eight adults age >or= 60 years with de novo CN-AML, enrolled onto Cancer and Leukemia Group B protocols 9720 and 10201, were studied at diagnosis for NPM1, FLT3, CEBPA, and WT1 mutations, and gene- and microRNA-expression profiles.

RESULTS

Patients with NPM1 mutations (56%) had higher complete remission (CR) rates (84% v 48%; P < .001) and longer disease-free survival (DFS; P = .047; 3-year rates, 23% v 10%) and overall survival (OS; P < .001; 3-year rates, 35% v 8%) than NPM1 wild-type patients. In multivariable analyses, NPM1 mutations remained independent predictors for higher CR rates (P < .001) and longer DFS (P = .004) and OS (P < .001), after adjustment for other prognostic clinical and molecular variables. Unexpectedly, the prognostic impact of NPM1 mutations was mainly observed in patients >or= 70 years. Gene- and microRNA-expression profiles associated with NPM1 mutations were similar across older patient age groups and similar to those in younger (< 60 years) patients with CN-AML. These profiles were characterized by upregulation of HOX genes and their embedded microRNAs and downregulation of the prognostically adverse MN1, BAALC, and ERG genes.

CONCLUSION

NPM1 mutations have favorable prognostic impact in older patients with CN-AML, especially those age >or= 70 years. The gene- and microRNA-expression profiles suggest that NPM1 mutations constitute a marker defining a biologically homogeneous entity in CN-AML that might be treated with specific and/or targeted therapies across age groups.

The shared tumor associated antigen cyclin-A2 is recognized by high-avidity T-cells

Cyclin-A2, a key cell cycle regulator, has been shown to be overexpressed in various types of malignancies with little expression in normal tissue. Such tumor-associated genes potentially are useful targets for cancer immunotherapy. However, high-avidity cyclin-specific T cells are considered to be thymically deleted. We identified at least one nonameric HLA-A*0201 binding cyclin-A2 epitope by a reverse immunology approach. Using a highly efficient T-cell expansion system that is based on CD40-activated B (CD40-B) cells as sole antigen-presenting cells we successfully generated cyclin-A2 specific CTL from HLA-A*0201(+) donors. Interestingly, high-avidity cyclin-A2 specific CTL lines, which recognized peptide-pulsed and antigen expressing target cells, were indeed generated by stimulation with CD40-B cells when pulsed with low concentrations of peptide, whereas CD40-B cells pulsed at saturating concentrations could only induce low-avidity CTL, which recognized peptide-pulsed target cells only. One high-avidity CTL line was subcloned and CTL clones, whose peptide concentration required for half-maximal lysis were less than 1 nM, could lyse cyclin-A2 expressing tumor cells. Taken together, cyclin A2 is an attractive candidate for immune intervention in a significant number of cancer patients and high-avidity T cells can be readily generated using CD40-B cells as antigen-presenting cells.

Expression of retinoic acid receptor alpha in the germline is essential for proper cellular association and spermiogenesis during spermatogenesis

Signaling through vitamin A metabolites is indispensable for spermatogenesis, and disruption of retinoic acid receptor alpha (RARalpha) function resulted in male sterility and aberrant spermatogenesis, which resembled vitamin A deficiency. Here we investigated the lineage- and cell-specific role of RARalpha-mediated signaling during spermatogenesis using germ-cell transplantation and genetically manipulated mouse models. We demonstrated that RARalpha-deficient germ-cell stem cells were able to repopulate germ-cell-depleted wild-type testes and initiate spermatogenesis; however, improper cellular associations and abnormal sperm formation were observed. We further generated RARalpha-deficient mice that expressed RARalpha-EGFP fusion protein uniquely in haploid germ cells. Strikingly, spermatid orientation, alignment and release, as well as sperm morphology, were normal and there was a partial rescue of sterility. These data provide the first direct evidence for a distinct requirement of RARalpha-mediated retinoid signaling specifically in germ cells.

NGF inhibits human leukemia proliferation by downregulating cyclin A1 expression through promoting acinus/CtBP2 association

Cyclin A1 is essential for leukemia progression, and its expression is tightly regulated by acinus, a nuclear speckle protein. However, the molecular mechanism of how acinus mediates cyclin A1 expression remains elusive. Here we show that transcription corepressor CtBP2 directly binds acinus, which is regulated by nerve growth factor (NGF), inhibiting its stimulatory effect on cyclin A1, but not cyclin A2, expression in leukemia. NGF, a cognate ligand for the neurotrophic receptor TrkA, promotes the interaction between CtBP2 and acinus through triggering acinus phosphorylation by Akt. Overexpression of CtBP2 diminishes cyclin A1 transcription, whereas depletion of CtBP2 abolishes NGF's suppressive effect on cyclin A1 expression. Strikingly, gambogic amide, a newly identified TrkA agonist, potently represses cyclin A1 expression, thus blocking K562 cell proliferation. Moreover, gambogic amide ameliorates the leukemia progression in K562 cells inoculated nude mice. Hence, NGF downregulates cyclin A1 expression through escalating CtBP2/acinus complex formation, and gambogic amide might be useful for human leukemia treatment.

Polo-like kinase 1 is overexpressed in acute myeloid leukemia and its inhibition preferentially targets the proliferation of leukemic cells

Polo-like kinase 1 (Plk1) is a major mitotic regulator overexpressed in many solid tumors. Its role in hematopoietic malignancies is still poorly characterized. In this study, we demonstrate that Plk1 is highly expressed in leukemic cell lines, and overexpressed in a majority of samples from patients with acute myeloid leukemia compared with normal progenitors. A pharmacologic inhibitor, BI2536, blocks proliferation in established cell lines, and dramatically inhibits the clonogenic potential of leukemic cells from patients. Plk1 knockdown by small interfering RNA also blocked proliferation of leukemic cell lines and the clonogenic potential of primary cells from patients. Interestingly, normal primary hematopoietic progenitors are less sensitive to Plk1 inhibition than leukemic cells, whose proliferation is dramatically decreased by the inhibitor. These results highlight Plk1 as a potentially interesting therapeutic target for the treatment of acute myeloid leukemia.

Post-translational modification of cyclin A1 is associated with staurosporine and TNFalpha induced apoptosis in leukemic cells

Understanding of molecular mechanisms underlying the effects of cell cycle proteins in response to the chemotherapeutic agents is of great importance for improving the efficacy of targeted therapeutics and overcoming resistance to chemotherapeutic agents. Staurosporine and tumor necrosis factor alpha (TNFalpha) are the therapeutic agents that inhibit tumor cell growth by inducing cell death. Staurosporine induces apoptosis through the intrinsic pathway, while TNFalpha trigger the cell death via the extrinsic apoptotic pathway. We have previously demonstrated that the cell cycle regulatory protein, cyclin A1 played an important role in the development of acute myeloid leukemia (AML), and cyclin A1 expression correlated with disease characteristics and patient outcome in leukemia. However, it remains unknown how cyclin A1 expression is regulated in leukemic cells treated with the therapeutic agents. Here, we demonstrate that cyclin A1 protein is regulated by proteasome-mediated ubiquitination and degradation in untreated U-937 cells. Interestingly, ubiquitination- and proteasomal-mediated degradation of cyclin A1 is prevented in cells treated with staurosporine or TNFalpha. Induction of apoptosis in U-937 cells by staurosporine or TNFalpha resulted in an increase in cyclin A1 protein expression, which correlated well with cyclin A1 protein modification and the activation of caspase-3. Blocking caspases activity by Z-VAD-FMK had no effect on the increased cyclin A1 expression, suggesting that cyclin A1 might be regulated by caspase-3 independent pathways. We further propose that CDC25C may be associated with cyclin A1 protein modification in response to staurosporine or TNFalpha treatment. Our results suggest that cyclin A1 protein is stabilized via post-transcriptional modification in response to apoptosis induced by staurosporine or TNFalpha.

Serine/arginine protein-specific kinase 2 promotes leukemia cell proliferation by phosphorylating acinus and regulating cyclin A1

Serine/arginine (SR) protein-specific kinase (SRPK), a family of cell cycle-regulated protein kinases, phosphorylate SR domain-containing proteins in nuclear speckles and mediate the pre-mRNA splicing. However, the physiologic roles of this event in cell cycle are incompletely understood. Here, we show that SRPK2 binds and phosphorylates acinus, an SR protein essential for RNA splicing, and redistributes it from the nuclear speckles to the nucleoplasm, resulting in cyclin A1 but not A2 up-regulation. Acinus S422D, an SRPK2 phosphorylation mimetic, enhances cyclin A1 transcription, whereas acinus S422A, an unphosphorylatable mutant, blocks the stimulatory effect of SRPK2. Ablation of acinus or SRPK2 abrogates cyclin A1 expression in leukemia cells and arrest cells at G(1) phase. Overexpression of acinus or SRPK2 increases leukemia cell proliferation. Furthermore, both SRPK2 and acinus are overexpressed in some human acute myelogenous leukemia patients and correlate with elevated cyclin A1 expression levels, fitting with the oncogenic activity of cyclin A1 in leukemia. Thus, our findings establish a molecular mechanism by which SR splicing machinery regulates cell cycle and contributes to leukemia tumorigenesis.

Dissecting the role of p53 phosphorylation in homologous recombination provides new clues for gain-of-function mutants

Regulation of homologous recombination (HR) represents the best-characterized DNA repair function of p53. The role of p53 phosphorylation in DNA repair is largely unknown. Here, we show that wild-type p53 repressed repair of DNA double-strand breaks (DSBs) by HR in a manner partially requiring the ATM/ATR phosphorylation site, serine 15. Cdk-mediated phosphorylation of serine 315 was dispensable for this anti-recombinogenic effect. However, without targeted cleavage of the HR substrate, serine 315 phosphorylation was necessary for the activation of topoisomerase I-dependent HR by p53. Moreover, overexpression of cyclin A1, which mimics the situation in tumors, inappropriately stimulated DSB-induced HR in the presence of oncogenic p53 mutants (not Wtp53). This effect required cyclin A1/cdk-mediated phosphorylation for stable complex formation with topoisomerase I. We conclude that p53 mutants have lost the balance between activation and repression of HR, which results in a net increase of potentially mutagenic DNA rearrangements. Our data provide new insight into the mechanism underlying gain-of-function of mutant p53 in genomic instability.

Multiple cellular mechanisms related to cyclin A1 in prostate cancer invasion and metastasis

BACKGROUND

Cyclin A1 is a cell cycle regulator that has been implicated in the progression of prostate cancer. Its role in invasion and metastasis of this disease has not been characterized.

METHODS

Immunohistochemistry and cDNA microarray analyses were used to assess protein and mRNA expression of cyclin A1 and proteins with roles in metastasis, including vascular endothelial growth factor (VEGF), metalloproteinase 2 (MMP2), and MMP9, in human prostate cancer. Transient transfection and infection with viral vectors expressing cyclin A1 and short hairpin RNA (shRNA) targeting cyclin A1 were used to study the effects of altered cyclin A1 expression in PC3 prostate cancer cells. The BrdU assay, annexin V staining, and invasion chambers were used to examine cyclin A1 effects on proliferation, apoptosis, and invasion, respectively. The role of cyclin A1 and androgen receptor (AR) in transcription of VEGF and MMP2 was assessed by promoter mutation and chromatin immunoprecipitation. The effect of cyclin A1 expression on tumor growth and metastasis was analyzed in a mouse model of metastasis. All statistical tests were two-sided.

RESULTS

Cyclin A1 protein and mRNA expression were statistically significantly higher in prostate cancers than in adjacent benign tissues. A statistically significant correlation between expression of cyclin A1 and of MMP2, MMP9, and VEGF was observed in prostate tumors from 482 patients (P values from Spearman rank correlation tests < .001). PC3 cells that overexpressed cyclin A1 showed increased invasiveness, and inhibition of cyclin A1 expression via shRNA expression reduced invasiveness of these cells. Eight of 10 mice (80%) bearing PC3 cells overexpressing cyclin A1 had infiltration of tumor cells in lymph node, liver, and lung, but all 10 mice bearing tumors expressing control vector were free of liver and lung metastases and only one mouse from this group had lymph node metastasis (P values from Fisher exact tests < .001). Cyclin A1, in concert with AR, bound to and increased expression from the VEGF and MMP2 promoters.

CONCLUSIONS

Cyclin A1 contributes to prostate cancer invasion by modulating the expression of MMPs and VEGF and by interacting with AR.

Six1 overexpression in mammary cells induces genomic instability and is sufficient for malignant transformation

Homeoproteins are transcription factors that act as master regulators of development and are frequently dysregulated in cancers. During embryogenesis, the Six1 homeoprotein is essential for the expansion of precursor cell populations that give rise to muscle and kidney, among other organs. Six1 overexpression is observed in numerous cancers, resulting in increased proliferation, survival, and metastasis. Here, we investigate whether Six1 can play a causal role in mammary tumor initiation. We show that Six1 overexpression in MCF12A mammary epithelial cells promotes multiple properties associated with malignant transformation, including increased proliferation, genomic instability, and anchorage-independent growth. We further show that this transformation is dependent on up-regulation of its transcriptional target, cyclin A1, which is normally expressed in the embryonic mammary gland but dramatically reduced in the adult gland. Six1-transformed MCF12A cells are tumorigenic in nude mice, forming aggressive tumors that are locally invasive and exhibit peritumoral lymphovascular invasion. In human breast carcinomas, expression of Six1 and cyclin A1 mRNA correlate strongly with each other (P < 0.0001), and expression of Six1 and cyclin A1 each correlate with Ki67, a marker of proliferation (P < 0.0001 and P = 0.014, respectively). Together, our data indicate that Six1 overexpression is sufficient for malignant transformation of immortalized, nontumorigenic mammary epithelial cells, and suggest that the mechanism of this transformation involves inappropriate reexpression of cyclin A1 in the adult mammary gland.

Interleukin-6 activates PI3K/Akt pathway and regulates cyclin A1 to promote prostate cancer cell survival

Interleukin-6 (IL6) is a growth and survival factor in human prostate cancer (PCa) cells with aggressive phenotypes and has been implicated in the progression of hormone refractory PCas. In the present study, we characterized the IL6-triggered PI3K/Akt and MAPK/Erk signaling. We identified the A-type cyclin, cyclin A1 as an important downstream target of PI3K/Akt. Treatment of cells with PI3K inhibitor or cotransfection with a vector expressing wild-type PTEN decreased cyclin A1 promoter activity. Cyclin A1 promoter activity and its expression were upregulated by constitutively active myristoylated Akt and were downregulated by dominant negative Akt in response to IL6 stimulation. LNCaP cells overexpressing cyclin A1 are resistant to camptothecin-induced apoptosis. Conversely, targeted knockdown of cyclin A1 via shRNA in LNCaP IL6+ cells resulted in decreased survival after treatment with camptothecin. This suggests that cyclin A1 is an important downstream target of PI3K/Akt that transduces survival signals in response to IL6 stimulation. Xenograft tumors generated from LNCaP-IL6+ cells expressing IL6 had higher levels of cyclin A1 and had rapid tumor growth compared to LNCaP xenograft tumors. Taken together, IL6 might utilize PI3K/Akt and cyclin A1 to promote tumor cell survival in PCa.

Review: genetic models of acute myeloid leukaemia

The use of genetically engineered mice (GEM) have been critical in understanding disease states such as cancer, and none more so than acute myelogenous leukaemia (AML), a disease characterized by over 100 distinct chromosomal translocations. A substantial proportion of cases exhibiting recurrent reciprocal translocations at diagnosis, such as t(8;21) or t(15;17) have been exhaustively studied and are currently employed in clinical diagnosis. However, a definitive conclusion regarding the leukaemogenic potential of defined transgenes for this disease remains elusive. While it is increasingly apparent that a number of cooperating mutations are necessary to develop a leukaemic phenotype, the number of models reflecting these synergisms remains few. Furthermore, little emphasis has been paid to the effect of chromosomal translocations other than recurrent genetic abnormalities, with no models reflecting the multiple abnormalities observed in high-risk cases of AML accounting for 8-10% of adult AML. Here we review the differing technologies employed in generation of GEM of AML. We discuss the relevance of GEM AML from embryonic stem cell-mediated (for example retinoic acid receptor-alpha fusions and AML1/ETO) models; through to the valuable retroviral-mediated gene transfer models. The latter have been used to great effect in defining the transforming properties of chromosomal translocation products such as MLL (found in 5-6% of all AML cases) and NUP98 (denoting poor prognosis in therapy-related disease) and particularly when co-transduced with bad prognostic factors such as Flt3 mutations. Finally, we comment on the emergence of newer transduction technologies, which can regulate the level of expression to defined cell lineages in both primary murine and human xenografts, and discuss how combining multiple genetic modalities, more relevant models of this complex disease are being generated.

Identification of genes with abnormal expression changes in acute myeloid leukemia

Acute myeloid leukemia (AML) is one of the most common and deadly forms of hematopoietic malignancies. We hypothesized that microarray studies could identify previously unrecognized expression changes that occur only in AML blasts. We were particularly interested in those genes with increased expression in AML, believing that these genes may be potential therapeutic targets. To test this hypothesis, we compared gene expression profiles between normal hematopoietic cells from 38 healthy donors and leukemic blasts from 26 AML patients. Normal hematopoietic samples included CD34+ selected cells (N = 18), unselected bone marrows (N = 10), and unselected peripheral bloods (N = 10). Twenty genes displayed AML-specific expression changes that were not found in the normal hematopoietic cells. Subsequent analyses using microarray data from 285 additional AML patients confirmed expression changes for 13 of the 20 genes. Seven genes (BIK, CCNA1, FUT4, IL3RA, HOMER3, JAG1, WT1) displayed increased expression in AML, while 6 genes (ALDHA1A, PELO, PLXNC1, PRUNE, SERPINB9, TRIB2) displayed decreased expression. Quantitative RT/PCR studies for the 7 over-expressed genes were performed in an independent set of 9 normal and 21 pediatric AML samples. All 7 over-expressed genes displayed an increased expression in the AML samples compared to normals. Three of the 7 over-expressed genes (WT1, CCNA1, and IL3RA) have already been linked to leukemogenesis and/or AML prognosis, while little is known about the role of the other 4 over-expressed genes in AML. Future studies will determine their potential role in leukemogenesis and their clinical significance.

Distinct roles for the mammalian A-type cyclins during oogenesis

There are two A-type cyclins in higher vertebrates, cyclin A1 and A2. Targeted mutagenesis has shown that cyclin A2 is essential for early embryonic development while cyclin A1 is required only for male meiosis. The embryonic lethality of cyclin A2 knockout mice has obviated understanding its role in other aspects of mammalian development, including the germ line. We reported previously that cyclin A2 expression in the male germ line is consistent with a role in both mitotic and meiotic cell cycles. Using in situ hybridization and immunohistochemistry, we now observe high levels of cyclin A2 in granulosa cells and less-abundant but readily detectable expression in ovarian and ovulated oocytes. A decrease in cyclin A2 protein was observed in oocytes from embryonic stages to post-natal and adult ovaries. Interestingly, cyclin A2 protein was nuclear in oocytes from embryonic day 13.5 to 15.5, changing to largely cytoplasmic in oocytes from embryonic day 16.5 to post-natal and adults. Readily detectable expression of the cyclin-dependent kinases Cdk1 and Cdk2, two common partners for the A-type cyclins, was observed in granulosa cells and oocytes at all stages of folliculogenesis. Cdk1 was predominantly cytoplasmic, whereas Cdk2 was both cytoplasmic and nuclear in oocytes. No cyclin A1 expression, at either the mRNA level or the protein level was detected in either embryonic or adult ovaries, consistent with the full fertility observed in female cyclin A1-deficient mice. These results suggest that in the female germ line, cyclin A2 but not cyclin A1 has distinct roles in both mitosis and meiosis.

Cyclin A1 expression and associations with disease characteristics in childhood acute lymphoblastic leukemia

A critical cell cycle regulatory protein, cyclin A1, has been implicated in the development of acute myeloid leukemia (AML). Here, we have examined the expression and clinical significance of cyclin A1 in childhood acute lymphoblastic leukemia (ALL). Cyclin A1 was highly expressed in lymphoblastic leukemic cell lines and in 22 of 30 ALL patients (73%). Cyclin A1 expression correlated with patient age (P=0.006), but not with cytogenetic abnormalities. Patients with high levels of cyclin A1 had poorer event-free survival (57.9%) compared to patients with lower levels (75%).

Increased expression of cyclin A1 protein is associated with all-trans retinoic acid-induced apoptosis

Deregulated cell growth and inhibition of apoptosis are hallmarks of cancer. All-trans retinoic acid induces clinical remission in patients with acute promyelocytic leukemia by inhibiting cell growth and inducing differentiation and apoptosis of the leukemic blasts. An important role of the cell cycle regulatory protein, cyclin A1, in the development of acute myeloid leukemia has previously been demonstrated in a transgenic mouse model. We have recently shown that there was a direct interaction between cyclin A1 and a major all-trans retinoic acid receptor, RAR alpha, following all-trans retinoic acid treatment of leukemic cells. In the present study, we investigated whether cyclin A1 might be involved in all-trans retinoic acid-induced apoptosis in U-937 leukemic cells. We found that all-trans retinoic acid-induced apoptosis was associated with concomitant increase in cyclin A1 expression. However, there was no induction of cyclin A1 mRNA expression following the all-trans retinoic acid-induced apoptosis. Treatment of cells with a caspase inhibitor was not able to prevent all-trans retinoic acid-induced up-regulation of cyclin A1 expression. Interestingly, induced cyclin A1 expression in U-937 cells led to a significant increase in the proportion of apoptotic cells. Further, U-937 cells overexpressing cyclin A1 appeared to be more sensitive to all-trans retinoic acid-induced apoptosis indicating the ability of cyclin A1 to mediate all-trans retinoic acid-induced apoptosis. Induced cyclin E expression was not able to initiate cell death in U-937 cells. Our results indicate that cyclin A1 might have a role in apoptosis by mediating all-trans retinoic acid-induced apoptosis.

A role for cyclin A1 in mediating the autocrine expression of vascular endothelial growth factor in prostate cancer

Elevated levels of cyclin A1 expression have been implicated in acute myeloid leukemia and in male germ cell tumors. However, a role of cyclin A1 in tumorigenesis of prostate cancer has not been reported. In the present study, expression of cyclin A1 in patients with prostate cancer and a role of cyclin A1 in mediating expression of vascular endothelial growth factor (VEGF) were investigated. Cyclin A1 was highly expressed in aggressive tumors and was significantly correlated with VEGF expression in 96 patients with prostate cancer. Treatment of LNCaP cells with R1881, a synthetic androgen resulted in increased cyclin A1 expression. Induction of cyclin A1 expression in LNCaP cells led to an increase in VEGF expression and this effect was manifested upon the R1881 treatment. Cyclin A1 failed to mediate VEGF activation in DU-145 cells lacking a functional Rb and an androgen receptor (AR). Although AR expression was induced into DU-145 cells, cyclin A1 was unable to mediate VEGF expression. However, induced coexpression of cyclin A1, Rb and AR in DU-145 cells in the presence of R1881 greatly promoted VEGF promoter activity. This suggests that cyclin A1 mediates VEGF expression in cooperation with Rb- and androgen-dependent pathways in prostate cancer.

The molecular pathogenesis of acute myeloid leukemia

The description of the molecular pathogenesis of acute myeloid leukemias (AML) has seen dramatic progress over the last years. Two major types of genetic events have been described that are crucial for leukemic transformation: alterations in myeloid transcription factors governing hematopoietic differentiation and activating mutations of signal transduction intermediates. These processes are highly interdependent, since the molecular events changing the transcriptional control in hematopoietic progenitor cells modify the composition of signal transduction molecules available for growth factor receptors, while the activating mutations in signal transduction molecules induce alterations in the activity and expression of several transcription factors that are crucial for normal myeloid differentiation. The purpose of this article is to review the current literature describing these genetic events, their biological consequences and their clinical implications. As the article will show, the recent description of several critical transforming mutations in AML may soon give rise to more efficient and less toxic molecularly targeted therapies of this deadly disease.

Interferon-gamma-induced gene expression in CD34 cells: identification of pathologic cytokine-specific signature profiles

Hematopoietic effects of interferon-gamma (IFN-gamma) may be responsible for certain aspects of the pathology seen in bone marrow failure syndromes, including aplastic anemia (AA), paroxysmal nocturnal hemoglobinuria (PNH), and some forms of myelodysplasia (MDS). Overexpression of and hematopoietic inhibition by IFN-gamma has been observed in all of these conditions. In vitro, IFN-gamma exhibits strong inhibitory effects on hematopoietic progenitor and stem cells. Previously, we have studied the transcriptome of CD34 cells derived from patients with bone marrow failure syndromes and identified characteristic molecular signatures common to some of these conditions. In this report, we have investigated genome-wide expression patterns after exposure of CD34 and bone marrow stroma cells derived from normal bone marrow to IFN-gamma in vitro and have detected profound changes in the transcription profile. Some of these changes were concordant in both stroma and CD34 cells, whereas others were specific to CD34 cells. In general, our results were in agreement with the previously described function of IFN-gamma in CD34 cells involving activation of apoptotic pathways and immune response genes. Comparison between the IFN-gamma transcriptome in normal CD34 cells and changes previously detected in CD34 cells from AA and PNH patients reveals the presence of many similarities that may reflect molecular signature of in vivo IFN-gamma exposure.

Expression of the cyclin-dependent kinase inhibitor p27 and its deregulation in mouse B cell lymphomas

CDKN1B (p27) regulates cell-cycle progression at the G1-S transition by suppressing the cyclin E/CDK2 kinase complex. In normal lymphocytes and most human B cell non-Hodgkin lymphomas (NHL), there is an inverse correlation between proliferative activity and expression of p27; however, a subset of NHL with high mitotic indices expresses p27, which is inactive due to sequestration in nuclear protein complexes or due to cytoplasmic retention. Our studies of mouse B cell NHL also identified cases with high proliferative activity and high levels of p27 at a surprisingly high frequency. Here, p27 was complexed with D-type cyclins 1 and 3 and with the COPS9 protein, JAB1. In addition, we found cytoplasmic sequestration following phosphorylation by activated AKT.

IgH and TCRgamma gene rearrangements, cyclin A1 and HOXA9 gene expression in biphenotypic acute leukemias

In this study we investigated IgH and TCRgamma gene rearrangements, cyclin A1 and HOXA9 gene expression as well as the in vitro growth of biphenotypic acute leukemia (BAL) blasts in relation to acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML). The aim of the study was to correlate BAL morphology and its biological parameters in order to get information that might be used for additional stratification of BAL. This rare form of AL was identified in a total of 10 patients, comprising 4.3% of adult and 3.0% of pediatric patients with de novo AL referred to our institution during the 1999-2003 period. Our results indicate that IgH and TCRgamma gene rearrangements correlated well with lymphoid BAL morphology, whereas the expression of cyclin A1 correlated with myeloid and undifferentiated BAL morphology. Surprisingly, HOXA9 expression, a marker associated with myeloid cell lineage, showed no strong correlation with BAL morphology. Finally, in vitro growth of blasts during a 7-day culture showed autonomous cell growth in 3/10 AML and 3/8 myeloid BAL samples tested, but not in any of the AL with lymphoid features. Further studies are needed to confirm these findings and to extend research to a broader spectrum of cell markers.

Cyclin A1, the alternative A-type cyclin, contributes to G1/S cell cycle progression in somatic cells

Cyclin A1 is an alternative A-type cyclin that is essential for spermatogenesis, but it is also expressed in hematopoietic progenitor cells and in acute myeloid leukemia. Its functions during cell cycle progression of somatic cells are incompletely understood. Here, we have analysed the cell cycle functions of cyclin A1 in transformed and nontransformed cells. Murine embryonic fibroblasts derived from cyclin A1-deficient mice were significantly impaired in their proliferative capacity. In accordance, cyclin A1-/- cells accumulated in G1 and G2/M phase while the percentage of S phase cells decreased. Also, lectin stimulated splenic lymphocytes from cyclin A1-/- mice proliferated slower than their wild-type counterparts. Forced cyclin A1 overexpression in NIH3T3 cells and in U937 leukemic cells either by transient transfection or by retroviral infection enhanced S phase entry. Consequently, siRNA mediated silencing of cyclin A1 in highly cyclin A1 expressing ML1 leukemic cells significantly slowed S phase entry, decreased proliferation and inhibited colony formation. Taken together, these analyses demonstrate that cyclin A1 contributes to G1 to S cell cycle progression in somatic cells. Cyclin A1 overexpression enhances S phase entry consistent with an oncogenic function. Finally, cyclin A1 might be a therapeutic target since its silencing inhibited leukemia cell growth.

Expression of cyclin A1 and cell cycle proteins in hematopoietic cells and acute myeloid leukemia and links to patient outcome

Abnormal expression of several key regulators essential for G1/S transitions has been implicated in tumorigenesis. A critical role of cyclin A1 in the development of acute myeloid leukemia (AML) has previously been demonstrated in transgenic mice. Our present study focused on the expression and prognostic significance of cyclin A1 and a panel of cell cycle regulatory proteins including cyclin A2, cyclin B1, cyclin E, CDK1, CDK2, p21 and p27 in bone marrow samples from 40 patients with AML. Freshly isolated CD34+ hematopoietic cells and bone marrow samples from 10 healthy donors were also assessed for cell type- and subcellular-specific expression of the cell cycle regulatory proteins. The level of cyclin A1 expression was the only factor that showed a significant correlation with patient outcome. In log-rank test stratified by levels of cyclin A1 expression, patients with high levels of cyclin A1 had significantly worse overall survival (OS) (P = 0.012) compared to those with low levels. Further, patients with high levels of cyclin A1 had significantly lower disease-free survival (DFS) (P = 0.028). Multivariate analysis indicated that cyclin A1 protein expression was an independent prognostic factor for predicting DFS (P = 0.035) and OS (P = 0.045). No correlation between cyclin A1 expression and age was found. However, expression of cyclin A2, cyclin B1, cyclin E, CDK1, CDK2, p21 and p27 did not show prognostic significance in these AML patients.

Animal models of acute myelogenous leukaemia - development, application and future perspectives

From the early inception of the transplant models through to contemporary genetic and xenograft models, evolution of murine leukaemic model systems have been critical to our general comprehension and treatment of cancer, and, more specifically, disease states such as acute myelogenous leukaemia (AML). However, even with modern advances in therapeutics and molecular diagnostics, the majority of AML patients die from their disease. Thus, in the absence of definitive in vitro models which precisely recapitulate the in vivo setting of human AMLs and failure of significant numbers of new drugs late in clinical trials, it is essential that murine AML models are developed to exploit more specific, targeted therapeutics. While various model systems are described and discussed in the literature from initial transplant models such as BNML and spontaneous murine leukaemia virus models, to the more definitive genetic and clinically significant NOD/SCID xenograft models, there exists no single compendium which directly assesses, reviews or compares the relevance of these models. Thus, the function of this article is to provide clinicians and experimentalists a chronological, comprehensive appraisal of all AML model systems, critical discussion on the elucidation of their roles in our understanding of AML and consideration to their efficacy in the development of AML chemotherapeutics.

The role of CREB as a proto-oncogene in hematopoiesis and in acute myeloid leukemia

CREB is a transcription factor that functions in glucose homeostasis, growth factor-dependent cell survival, and memory. In this study, we describe a role of CREB in human cancer. CREB overexpression is associated with increased risk of relapse and decreased event-free survival. CREB levels are elevated in blast cells from patients with acute myeloid leukemia. To understand the role of CREB in leukemogenesis, we studied the biological consequences of CREB overexpression in primary human leukemia cells, leukemia cell lines, and transgenic mice. Our results demonstrate that CREB promotes abnormal proliferation and survival of myeloid cells in vitro and in vivo through upregulation of specific target genes. Thus, we report that CREB is implicated in myeloid cell transformation.

Stroma-Mediated Dysregulation of Myelopoiesis in Mice Lacking IκBα

Hematopoiesis occurs in the liver and the bone marrow (BM) during murine development. Newborn mice with a ubiquitous deletion of I kappa B alpha develop a severe hematological disorder characterized by an increase of granulocyte/erythroid/monocyte/macrophage colony-forming units (CFU-GEMM) and hypergranulopoiesis. Here, we report that this particular myeloproliferative disturbance is mediated by continuously deregulated perinatal expression of Jagged1 in I kappa B alpha-deficient hepatocytes. The result is a permanent activation of Notch1 in neutrophils. In contrast, in mice with a conditional deletion of I kappa B alpha only in the myeloid lineage (ikba(flox/flox) x LysM-Cre) and in fetal liver cell chimeras (ikba(FL delta/FL delta)), a cell-autonomous induction of the myeloproliferative disease was not observed. Coculture of I kappa B alpha-deficient hepatocytes with wild-type (wt) BM cells induced a Jagged1-dependent increase in CFUs. In summary, we show that cell-fate decisions leading to a premalignant hematopoietic disorder can be initiated by nonhematopoietic cells with inactive I kappa B alpha.

Regulation of the cyclin A1 protein is associated with its differential subcellular localization in hematopoietic and leukemic cells

An important role of the cell cycle regulatory protein cyclin A1 in the development of acute myeloid leukemia (AML) was previously demonstrated in a transgenic mouse model. We have now turned our attention to study specific aspects of the activity and subcellular distribution of cyclin A1 using bone marrow samples from normal donors and patients with AML, as well as leukemic cell lines. We show that the localization of cyclin A1 in normal hematopoietic cells is nuclear, whereas in leukemic cells from AML patients and cell lines, it is predominantly cytoplasmic. In leukemic cell lines treated with all-trans retinoic acid (ATRA), cyclin A1 localized to the nucleus. Further, there was a direct interaction between cyclin A1 and cyclin-dependent kinase 1, as well as a major ATRA receptor, RARalpha, in ATRA-treated cells but not in untreated leukemic cells. Our results indicate that the altered intracellular distribution of cyclin A1 in leukemic cells correlates with the status of the leukemic phenotype.

Systems Biology and the Molecular Circuits of Cancer

Proliferative disorders are a major challenge for human health. The understanding of the organization of cell-cycle events is of the utmost importance to devise effective therapeutic strategies for cancer. The awareness that cells and organisms are complex, modular, hierarchical systems and the availability of genome-wide gene expression and protein analyses, should make it feasible to elucidate human diseases in terms of dysfunctions of molecular systems. Here we review evidence in support of a systems model of the cell cycle, in which two sequential growth-sensitive thresholds control entry into S-phase. The putative molecular determinants that set the threshold for entry into S-phase are consistently altered in cancer cells. Such a framework could be useful in guiding both experimental investigation and data analysis by allowing wiring to other relevant cell modules thereby highlighting the differential responses, or lack of response of cancer cells to intra- and extracellular factors. Pharmacological approaches that take advantage of transformation-induced fragility to glucose shortage are discussed. Extension of this hierarchical, modular approach to tumors as a whole holds promise for the development of effective drug discovery approaches and more efficient therapeutic protocols.

Identification of interaction partners and substrates of the cyclin A1-CDK2 complex

The CDK2-associated cyclin A1 is essential for spermatogenesis and contributes to leukemogenesis. The detailed molecular functions of cyclin A1 remain unclear, since the molecular networks involving cyclin A1-CDK2 have not been elucidated. Here, we identified novel cyclin A1/CDK2 interaction partners in a yeast triple-hybrid approach. Several novel proteins (INCA1, KARCA1, and PROCA1) as well as the known proteins GPS2 (G-protein pathway suppressor 2), Ku70, receptor for activated protein kinase C1/guanine nucleotide-binding protein beta-2-like-1, and mRNA-binding motif protein 4 were identified as interaction partners. These proteins link the cyclin A1-CDK2 complex to diverse cellular processes such as DNA repair, signaling, and splicing. Interactions were confirmed by GST pull-down assays and co-immunoprecipitation. We cloned and characterized the most frequently isolated unknown gene, which we named INCA1 (inhibitor of CDK interacting with cyclin A1). The nuclear INCA1 protein is evolutionarily conserved and lacks homology to any known gene. This novel protein and two other interacting partners served as substrates for the cyclin A1-CDK2 kinase complex. Cyclin A1 and all interaction partners were highly expressed in testis with varying degrees of tissue specificity. The highest expression levels were observed at different time points during testis maturation, whereas expression levels in germ cell cancers and infertile testes decreased. Taken together, we identified testicular interaction partners of the cyclin A1-CDK2 complex and studied their expression pattern in normal organs, testis development, and testicular malignancies. Thereby, we establish a new basis for future functional analyses of cyclin A1. We provide evidence that the cyclin A1-CDK2 complex plays a role in several signaling pathways important for cell cycle control and meiosis.

Cyclin A2 mediates cardiomyocyte mitosis in the postmitotic myocardium

Cell cycle withdrawal limits proliferation of adult mammalian cardiomyocytes. Therefore, the concept of stimulating myocyte mitotic divisions has dramatic implications for cardiomyocyte regeneration and hence, cardiovascular disease. Previous reports describing manipulation of cell cycle proteins have not shown induction of cardiomyocyte mitosis after birth. We now report that cyclin A2, normally silenced in the postnatal heart, induces cardiac enlargement because of cardiomyocyte hyperplasia when constitutively expressed from embryonic day 8 into adulthood. Cardiomyocyte hyperplasia during adulthood was coupled with an increase in cardiomyocyte mitosis, noted in transgenic hearts at all time points examined, particularly during postnatal development. Several stages of mitosis were observed within cardiomyocytes and correlated with the nuclear localization of cyclin A2. Magnetic resonance analysis confirmed cardiac enlargement. These results reveal a previously unrecognized critical role for cyclin A2 in mediating cardiomyocyte mitosis, a role that may significantly impact upon clinical treatment of damaged myocardium.