Lineage-specific regulation of cell cycle control gene expression during haematopoietic cell differentiation

Immunophenotypic expression profile of multiple myeloma cases at a tertiary hospital in Nairobi Kenya

Introduction

Multiple myeloma (MM) is a plasma cell neoplasm that constitutes 10-15% of all hematopoietic neoplasms. Kenya is placed among the top five African countries for MM incidence and MM-related mortality. Prior studies have suggested that the aberrant expression of Cyclin D1, CD56, CD117 and Ki-67 on neoplastic plasma cells is useful in disease prognostication. The prevalence and significance of expression of these markers in a cohort of MM cases in Kenya has not been studied previously.

Methods

A retrospective cross-sectional study was carried out at the Aga Khan University Hospital, Nairobi. The study population included 83 MM cases with available trephine blocks archived between 1st of January 2009 and 31st of March 2020. Immunohistochemical expression of Cyclin D1, CD56, CD117, and Ki-67 was analyzed and scored. The biomarkers were described using frequencies based on the positive and negative results. Fisher's exact test was used to determine the association between the immunophenotypic markers and categorical variables.

Results

Of the 83 selected cases, expression of Cyclin D1, CD56, CD117 and Ki-67 was identified in 28.9, 34.9, 7.2, and 50.6%, respectively. Cyclin D1 positivity was significantly associated with hypercalcemia. Absence of CD117 expression was noted to be associated with adverse risk parameters including an IgA isotype or light chain disease, International Staging System (ISS) stage III disease, abnormal baseline serum free light chains (sFLC) and a high plasma cell burden.

Conclusion

Cyclin D1 expression was congruent with previously reported studies. The frequency of CD56 and CD117 expression was lower than previously reported. This may be due to differences in disease biology between the study populations. Approximately half of cases were Ki-67 positive. Our data showed limited associations between the expression of studied markers and clinicopathologic variables. However, this could be attributed to the small study sample size. We would recommend further characterization of the disease in a larger prospective study with the inclusion of survival outcomes and cytogenetic studies.

Matrix Stiffness Activating YAP/TEAD1-Cyclin B1 in Nucleus Pulposus Cells Promotes Intervertebral Disc Degeneration

Intervertebral disc degeneration is a leading cause of disability in the elderly population. Rigid extracellular matrix is a critical pathological feature of disc degeneration, leading to aberrant nucleus pulposus cells (NPCs) proliferation. However, the underlying mechanism is unclear. Here, we hypothesize that increased matrix stiffness induces proliferation and thus degenerative phenotypes of NPCs through YAP/TEAD1 signaling pathway. We established hydrogel substrates to mimic stiffness of degenerated human nucleus pulposus tissues. RNA-sequencing identified differentially expressed genes between primary rat NPCs cultured on rigid and soft hydrogels. Dual luciferase assay and gain- and loss-function experiments evaluated the correlation between YAP/TEAD1 and Cyclin B1. Furthermore, single-cell RNA-sequencing of human NPCs was performed to identify specific cell clusters with high YAP expression. Matrix stiffness increased in severely degenerated human nucleus pulposus tissues (p < 0.05). Rigid substrate enhanced rat NPCs proliferation mainly through Cyclin B1, which was directly targeted and positively regulated by YAP/TEAD1. Depletion of YAP or Cyclin B1 arrested G2/M phase progression of rat NPCs and reduced fibrotic phenotypes including MMP13 and CTGF (p < 0.05). Fibro NPCs with high YAP expression were identified in human tissues and responsible for fibrogenesis during degeneration. Furthermore, inhibition of YAP/TEAD interaction by verteporfin suppressed cell proliferation and alleviated degeneration in the disc needle puncture model (p < 0.05). Our results demonstrate that elevated matrix stiffness stimulates fibro NPCs proliferation through YAP/TEAD1-Cyclin B1 axis, indicating a therapeutic target for disc degeneration.

Mesenchymal Stromal Cell-Derived Extracellular Vesicles Modulate Hematopoietic Stem and Progenitor Cell Viability and the Expression of Cell Cycle Regulators in an Age-dependent Manner

Aging of the hematopoietic system is characterized by an expansion of hematopoietic stem and progenitor cells (HSPCs) with reduced capacity for engraftment, self-renewal, and lymphoid differentiation, resulting in myeloid-biased hematopoiesis. This process is mediated by both HSPC intrinsic and extrinsic factors, e.g., the stromal environment. A relevant cellular component of the bone marrow (BM) microenvironment are mesenchymal stromal cells (MSCs) which regulate fate and differentiation of HSPCs. The bi-directional communication with HSPCs is mediated either by direct cell-cell contacts or by extracellular vesicles (EVs) which carry bioactive substances such as small RNA, DNA, lipids and proteins. So far, the impact of MSC-derived EVs on human hematopoietic aging is poorly investigated. BM MSCs were isolated from young (n = 3, median age: 22 years) and aged (n = 3, median age: 70 years) donors and the EVs were isolated after culturing the confluent cell layer in serum-free medium for 48 h. CD34⁺ HSPCs were purified from peripheral blood of healthy donors (n = 3, median age: 65 years) by magnetic sorting. Nanoparticle tracking analysis (NTA), transmission electron microscopy (TEM) and western blot detection of EV markers CD63, CD81 and Flotillin-1 revealed no significant differences between young and aged MSC-EVs. Interestingly, young MSCs secreted a significantly higher miRNA concentration than aged cells. However, the amount of distinct miRNAs such as miR-29a and miR-34a was significantly higher in aged MSC-EVs. HSPCs incubated with young EVs showed a significant increase in cell number and a higher viability. The expression of the tumor suppressors PTEN, a known target of mir-29a, and CDKN2A was increased in HSPCs incubated with young EVs. The clonogenic assay demonstrated a decreased colony number of CFU-GM after treatment with young EVs and an increased number of BFU-E/CFU-E after incubation with aged MSC-EVs. Xenogenic transplantation experiments showed no significant differences concerning the engraftment of lymphoid or myeloid cell compartments, but the overall human chimerism 8–16 weeks after transplantation was higher after EV treatment. In conclusion, our data suggest that HSPC characteristics such as cell cycle activity and clonogenicity can be modulated by MSC-derived EVs. Further studies have to elucidate the potential therapeutic relevance of our findings.

BCL-2 Inhibitor ABT-737 Effectively Targets Leukemia-Initiating Cells with Differential Regulation of Relevant Genes Leading to Extended Survival in a NRAS/BCL-2 Mouse Model of High Risk-Myelodysplastic Syndrome

During transformation, myelodysplastic syndromes (MDS) are characterized by reducing apoptosis of bone marrow (BM) precursors. Mouse models of high risk (HR)-MDS and acute myelogenous leukemia (AML) post-MDS using mutant NRAS and overexpression of human BCL-2, known to be poor prognostic indicators of the human diseases, were created. We have reported the efficacy of the BCL-2 inhibitor, ABT-737, on the AML post-MDS model; here, we report that this BCL-2 inhibitor also significantly extended survival of the HR-MDS mouse model, with reductions of BM blasts and lineage negative/Sca1+/KIT+ (LSK) cells. Secondary transplants showed increased survival in treated compared to untreated mice. Unlike the AML model, BCL-2 expression and RAS activity decreased following treatment and the RAS:BCL-2 complex remained in the plasma membrane. Exon-specific gene expression profiling (GEP) of HR-MDS mice showed 1952 differentially regulated genes upon treatment, including genes important for the regulation of stem cells, differentiation, proliferation, oxidative phosphorylation, mitochondrial function, and apoptosis; relevant in human disease. Spliceosome genes, found to be abnormal in MDS patients and downregulated in our HR-MDS model, such as Rsrc1 and Wbp4, were upregulated by the treatment, as were genes involved in epigenetic regulation, such as DNMT3A and B, upregulated upon disease progression and downregulated upon treatment.

Specific Smad2/3 Linker Phosphorylation Indicates Esophageal Non-neoplastic and Neoplastic Stem-Like Cells and Neoplastic Development

BACKGROUND

There is little known about stem cells in human non-neoplastic and neoplastic esophageal epithelia. We have demonstrated expression of linker threonine-phosphorylated Smad2/3 (pSmad2/3L-Thr), suggesting presence of stem-like cells in mouse esophageal epithelium, and identified presence of pSmad2/3L-Thr-positive cells that might function as cancer stem cells in mouse model of colorectal carcinoma.

AIMS

We explore whether pSmad2/3L-Thr can be used as a biomarker for stem cells of human esophageal epithelia and/or neoplasms.

METHODS

We have used esophageal tissues from inpatients undergoing endoscopic submucosal dissection and performed double immunofluorescent staining of pSmad2/3L-Thr and Ki67, CDK4, p63, Sox2, CK14, p53, ALDH1, CD44 or D2-40 after which the sections were stained with hematoxylin and eosin.

RESULTS

pSmad2/3L-Thr-positive cells showed immunohistochemical co-localization with CDK4, p63, CD44 and Sox2 in the basal and parabasal layers of non-neoplastic esophageal epithelia. In esophageal neoplasms, they showed immunohistochemical co-localization with p53, CDK4, ALDH1 and CD44. There was a significant increase in the percentage of pSmad2/3L-Thr-positive cells in the p53-positive neoplastic cell population with development of esophageal neoplasia. pSmad2/3L-Thr-positive cells localized to the lower section of low-grade intraepithelial neoplasia and were observed up to the upper section in carcinoma in situ. In invasive squamous cell carcinoma, they were scattered throughout the tumor with disappearance of polarity and were found in intraepithelial primary lesions and sites of submucosal and vessel invasion.

CONCLUSIONS

We determined significant expression of pSmad2/3L-Thr in human esophageal non-neoplastic and neoplastic epithelia, indicating that these are epithelial stem-like cells and cancer stem cells, respectively, that correlate with developing esophageal neoplasms.

Immunomodulatory drugs downregulate IKZF1 leading to expansion of hematopoietic progenitors with concomitant block of megakaryocytic maturation

The immunomodulatory drugs, lenalidomide and pomalidomide yield high response rates in multiple myeloma patients, but are associated with a high rate of thrombocytopenia and increased risk of secondary hematologic malignancies. Here, we demonstrate that the immunomodulatory drugs induce self-renewal of hematopoietic progenitors and upregulate megakaryocytic colonies by inhibiting apoptosis and increasing proliferation of early megakaryocytic progenitors via down-regulation of IKZF1. In this process, the immunomodulatory drugs degrade IKZF1 and subsequently down-regulate its binding partner, GATA1. This results in the decrease of GATA1 targets such as ZFPM1 and NFE2, leading to expansion of megakaryocytic progenitors with concomitant inhibition of maturation of megakaryocytes. The down-regulation of GATA1 further decreases CCND1 and increases CDKN2A expression. Overexpression of GATA1 abrogated the effects of the immunomodulatory drugs and restored maturation of megakaryocytic progenitors. Our data not only provide the mechanism for the immunomodulatory drugs induced thrombocytopenia but also help to explain the higher risk of secondary malignancies and long-term cytopenia induced by enhanced cell cycling and subsequent exhaustion of the stem cell pool.

Single cell transcriptomics reveals unanticipated features of early hematopoietic precursors

Molecular changes underlying stem cell differentiation are of fundamental interest. scRNA-seq on murine hematopoietic stem cells (HSC) and their progeny MPP1 separated the cells into 3 main clusters with distinct features: active, quiescent, and an un-characterized cluster. Induction of anemia resulted in mobilization of the quiescent to the active cluster and of the early to later stage of cell cycle, with marked increase in expression of certain transcription factors (TFs) while maintaining expression of interferon response genes. Cells with surface markers of long term HSC increased the expression of a group of TFs expressed highly in normal cycling MPP1 cells. However, at least Id1 and Hes1 were significantly activated in both HSC and MPP1 cells in anemic mice. Lineage-specific genes were differently expressed between cells, and correlated with the cell cycle stages with a specific augmentation of erythroid related genes in the G2/M phase. Most lineage specific TFs were stochastically expressed in the early precursor cells, but a few, such as Klf1, were detected only at very low levels in few precursor cells. The activation of these factors may correlate with stages of differentiation. This study reveals effects of cell cycle progression on the expression of lineage specific genes in precursor cells, and suggests that hematopoietic stress changes the balance of renewal and differentiation in these homeostatic cells.

miR-125b modulates megakaryocyte maturation by targeting the cell-cycle inhibitor p19INK4D

A better understanding of the mechanisms involved in megakaryocyte maturation will facilitate the generation of platelets in vitro and their clinical applications. A microRNA, miR-125b, has been suggested to have important roles in the self-renewal of megakaryocyte-erythroid progenitors and in platelet generation. However, miR-125b is also critical for hematopoietic stem cell self-renewal. Thus, the function of miR-125b and the complex signaling pathways regulating megakaryopoiesis remain to be elucidated. In this study, an attentive examination of the endogenous expression of miR-125b during megakaryocyte differentiation was performed. Accordingly, the differentiation of hematopoietic stem cells requires the downregulation of miR-125b, whereas megakaryocyte determination and maturation synchronize with miR-125b accumulation. The overexpression of miR-125b improves megakaryocytic differentiation of K562 and UT-7 cells. Furthermore, stage-specific overexpression of miR-125b in primary cells demonstrates that miR-125b mediates an enhancement of megakaryocytic differentiation after megakaryocyte determination, the stage at which megakaryocytes are negative for the expression of the hematopoietic progenitor marker CD34. The identification of miR-125b targets during megakaryopoiesis was focused on negative regulators of cell cycle because the transition of the G1/S phase has been associated with megakaryocyte polyploidization. Real-time PCR, western blot and luciferase reporter assay reveal that p19^INK4D is a direct target of miR-125b. P19^INK4D knockdown using small interfering RNA (siRNA) in megakaryocyte-induced K562 cells, UT-7 cells and CD61⁺ promegakaryocytes results in S-phase progression and increased polyploidy, as well as improved megakaryocyte differentiation, similarly to the effects of miR-125b overexpression. P19^INK4D overexpression reverses these effects, as indicated by reduced expression of megakaryocyte markers, G1-phase arrest and polyploidy decrease. P19^INK4D knockdown in miR-125b downregulated cells or p19^INK4D overexpression in miR-125b upregulated cells rescued the effect of miR-125b. Taken together, these findings suggest that miR-125b expression positively regulates megakaryocyte development since the initial phases of megakaryocyte determination, and p19^INK4D is one of the key mediators of miR-125b activity during the onset of megakaryocyte polyploidization.

Smad2/3 linker phosphorylation is a possible marker of cancer stem cells and correlates with carcinogenesis in a mouse model of colitis-associated colorectal cancer

BACKGROUND

Epithelial cells affected by somatic mutations undergo transition from a tumour-suppressive to a carcinogenic Smad pathway during sporadic colorectal carcinogenesis, and the specific linker threonine phosphorylation of Smad2/3 in colon epithelial cells indicates stem-like cells. This study extends previous observations to a model of colitis-associated colorectal cancer.

METHODS

After Crl:CD-1 mice received an administration of azoxymethane [AOM], the mice were given dextran sodium sulfate [DSS] for 7 days. AOM/DSS-treated mice [AOM/DSS mice] were killed at 10 or 20 weeks. After macroscopic observations, a histopathological analysis was conducted. Immunohistochemical staining was performed using the avidin-biotin immunoperoxidase method [pSmad3C-Ser, pSmad3L-Ser, c-Myc] and immunofluorescent methods [Ki67, β-catenin, CDK4, cyclin D1, Sox9, pSmad2/3L-Thr].

RESULTS

The colons from AOM/DSS mice were shorter than those from control mice. The number of colon tumours at Week 20 was higher than at Week 10. The inflammation scores for AOM/DSS mice were greater than those for control mice. Immunostaining-positive cells (staining by Ki67, β-catenin [nuclear and cytoplasmic], cyclin D1, and Sox9) were diffusely distributed in colon tumours. The percentage of pSmad3L-Ser-positive cells in colon tumours was higher than in sites of pre-neoplastic colitis, and that in sites of pre-neoplastic colitis was higher than in control mice. pSmad2/3L-Thr-positive cells were sparsely detected around crypt bases in non-neoplastic colon epithelia and at the tops of tumours, and immunohistochemical co-localisation of pSmad2/3L-Thr with Ki67 was not observed. Immunohistochemical co-localisation of pSmad2/3L-Thr with β-catenin and CDK4 was observed.

CONCLUSIONS

pSmad3L-Ser signalling is an early event in colitis-associated colorectal cancer, and pSmad2/3L-Thr immunostaining-positive cells might be cancer stem cells.

Phosphorylation of Smad2/3 at specific linker threonine indicates slow-cycling intestinal stem-like cells before reentry to cell cycle

BACKGROUND

Quiescent (slow-cycling) and active (rapid-cycling) stem cells are demonstrated in small intestines. We have identified significant expression of Smad2/3, phosphorylated at specific linker threonine residues (pSmad2/3L-Thr), in murine stomach, and suggested these cells are epithelial stem cells.

AIM

Here, we explore whether pSmad2/3L-Thr could serve as a biomarker for small intestine and colon stem cells.

METHODS

We examined small intestines and colons from C57BL/6 mice and colons with dextran sulfate sodium (DSS)-induced colitis. We performed double-immunofluorescent staining of pSmad2/3L-Thr with Ki67, cytokeratin 8, chromogranin A, CDK4, DCAMKL1, and Musashi-1. Small intestines and colons from Lgr5-EGFP knock-in mice were examined by pSmad2/3L-Thr immunofluorescent staining. To examine BrdU label retention of pSmad2/3L-Thr immunostaining-positive cells, we collected specimens after BrdU administration and observed double-immunofluorescent staining of pSmad2/3L-Thr with BrdU.

RESULTS

In small intestines and colons, pSmad2/3L-Thr immunostaining-strongly positive cells were detected around crypt bases. Immunohistochemical co-localization of pSmad2/3L-Thr with Ki67 was not observed. pSmad2/3L-Thr immunostaining-strongly positive cells showed co-localization with cytokeratin 8, CDK4, and Musashi-1 and different localization from chromogranin A and DCAMKL1 immunostaining-positive cells. Under a light microscope, pSmad2/3L-Thr immunostaining-strongly positive cells were morphologically undifferentiated. In Lgr5-EGFP knock-in mice, some but not all pSmad2/3L-Thr immunostaining-strongly positive cells showed co-localization with Lgr5. pSmad2/3L-Thr immunostaining-strongly positive cells showed co-localization with BrdU at 5, 10, and 15 days after administration. In DSS-induced colitis, pSmad2/3L-Thr and Ki67 immunostaining-positive cells increased in the regeneration phase and decreased in the injury phase.

CONCLUSION

In murine small intestines and colons, we suggest pSmad2/3L-Thr immunostaining-strongly positive cells are epithelial stem-like cells just before reentry to the cell cycle.

Developmental and oncogenic radiation effects on neural stem cells and their differentiating progeny in mouse cerebellum

Neural stem cells are highly susceptible to radiogenic DNA damage, however, little is known about their mechanisms of DNA damage response (DDR) and the long-term consequences of genotoxic exposure. Patched1 heterozygous mice (Ptc1(+/-)) provide a powerful model of medulloblastoma (MB), a frequent pediatric tumor of the cerebellum. Irradiation of newborn Ptc1(+/-) mice dramatically increases the frequency and shortens the latency of MB. In this model, we investigated the mechanisms through which multipotent neural progenitors (NSCs) and fate-restricted progenitor cells (PCs) of the cerebellum respond to DNA damage induced by radiation, and the long-term developmental and oncogenic consequences. These responses were assessed in mice exposed to low (0.25 Gy) or high (3 Gy) radiation doses at embryonic day 13.5 (E13.5), when NSCs giving rise to the cerebellum are specified but the external granule layer (EGL) has not yet formed, or at E16.5, during the expansion of granule PCs to form the EGL. We found crucial differences in DDR and apoptosis between NSCs and fate-restricted PCs, including lack of p21 expression in NSCs. NSCs also appear to be resistant to oncogenesis from low-dose radiation exposure but more vulnerable at higher doses. In addition, the pathway to DNA repair and the pattern of oncogenic alterations were strongly dependent on age at exposure, highlighting a differentiation-stage specificity of DNA repair pathways in NSCs and PCs. These findings shed light on the mechanisms used by NSCs and PCs to maintain genome integrity during neurogenesis and may have important implications for radiation risk assessment and for development of targeted therapies against brain tumors.

Tumor suppressor gene p16/INK4A/CDKN2A-dependent regulation into and out of the cell cycle in a spontaneous canine model of breast cancer

p16/INK4A/CDKN2A is an important tumor suppressor gene that arrests cell cycle in G1 phase inhibiting binding of CDK4/6 with cyclin D1, leaving the Rb tumor suppressor protein unphosphorylated and E2F bound and inactive. We hypothesized that p16 has a role in exit from cell cycle that becomes defective in cancer cells. Well characterized p16-defective canine mammary cancer cell lines (CMT28, CMT27, and CMT12), derived stably p16-transfected CMT cell clones (CMT27A, CMT27H, CMT28A, and CMT28F), and normal canine fibroblasts (NCF), were used to investigate expression of p16 after serum starvation into quiescence followed by re-feeding to induce cell cycle re-entry. The parental CMT cell lines used lack p16 expression either at the mRNA or protein expression levels, while p27 and other p16-associated proteins, including CDK4, CDK6, cyclin D1, and Rb, were expressed. We have successfully demonstrated cell cycle arrest and relatively synchronous cell cycle re-entry in parental CMT12, CMT28 and NCF cells as well as p16 transfected CMT27A, CMT27H, CMT28A, and CMT28F cells and confirmed this by (3)H-thymidine incorporation and flow cytometric analysis of cell cycle phase distribution. p16-transfected CMT27A and CMT27H cells exited cell cycle post-serum-starvation in contrast to parental CMT27 cells. NCF, CMT27A, and CMT28F cells expressed upregulated levels of p27 and p16 mRNA, post-serum starvation, as cells exited cell cycle and entered quiescence. Because quiescence and differentiation are associated with increased levels of p27, our data demonstrating that p16 was upregulated along with p27 during quiescence, suggests a potential role for p16 in maintaining these non-proliferative states.

Phosphorylation of Smad2/3 at the specific linker threonine residue indicates slow-cycling esophageal stem-like cells before re-entry to the cell cycle

The stem cell compartment in the esophageal epithelium is possibly located in the basal layer. We have identified significant expression of Smad2/3, phosphorylated at specific linker threonine residues (pSmad2/3L-Thr), in the epithelial cells of murine stomach and intestine, and have suggested that these cells are epithelial stem cells. In this study, we explore whether pSmad2/3L-Thr could serve as a biomarker for esophageal stem cells. We examined esophageal tissues from normal C57BL/6 mice and those with esophagitis. Double immunofluorescent staining of pSmad2/3L-Thr with Ki67, CDK4, p63, or CK14 was performed. After immunofluorescent staining, we stained the same sections with hematoxylin-eosin and observed these cells under a light microscope. We used the 5-bromo-2-deoxyuridine (BrdU) labeling assay to examine label retention of pSmad2/3L-Thr immunostaining-positive cells. We collected specimens 5, 10, 15 and 20 days after repeated BrdU administrations and observed double immunofluorescent staining of pSmad2/3L-Thr with BrdU. In the esophagus, pSmad2/3L-Thr immunostaining-positive cells were detected in the basal layer. These cells were detected between Ki67 immunostaining-positive cells, but they were not co-localized with Ki67. pSmad2/3L-Thr immunostaining-positive cells showed co-localization with CDK4, p63, and CK14. Under a light microscope, pSmad2/3L-Thr immunostaining-positive cells indicated undifferentiated morphological features. Until 20 days follow-up period, pSmad2/3L-Thr immunostaining-positive cells were co-localized with BrdU. pSmad2/3L-Thr immunostaining-positive cells significantly increased in the regeneration phase of esophagitis mucosae, as compared with control mice (esophagitis vs.

CONTROL

6.889 ± 0.676/cm vs. 4.293 ± 0.659/cm; P < 0.001). We have identified significant expression of pSmad2/3L-Thr in the specific epithelial cells of murine esophagi. We suggest that these cells are slow-cycling epithelial stem-like cells before re-entry to the cell cycle.

Expression and promoter methylation changes of the P15INK4b during ex vivo cord blood CD34+ cell expansion following co-culture with mesenchymal stromal cells

BACKGROUND

Because of the insufficient number of cord blood hematopoietic stem cells (CB-HSC), expansion of these cells seems to be important for clinical application in adults. Cell cycle inhibitors are important regulators in normal hematopoietic regeneration. In this study, mRNA expression and promoter methylation status of p15(INK4b) were evaluated during CB-HSC ex vivo expansion using cytokines and in co-culture system with a mesenchymal stem cells (MSCs) feeder layer.

METHODS

ex vivo cultures of CB-HSCs were performed in three culture conditions for 14 days: cytokines with an MSCs feeder layer, cytokines without a MSCs feeder layer, and co-culture with MSCs without cytokines. After expansion, measuring the total number of cells, CD34(+) cells, and CFU assay was performed. Methylation status of the p15(INK4b) gene promoter was analyzed using methylation-specific polymerase chain reaction and p15 mRNA expression was evaluated by real-time reverse transcriptase polymerase chain reaction.

RESULTS

Maximum CB-HSC expansion was observed on day 10 of expansion. The data showed that after 10 days, p15 mRNA expression in the expanded cells in all the three culture conditions was higher than in CD34(+) fresh cells (P < 0.01). p15 gene promoter of expanded CD34(+) cells remained in an unmethylated form just like fresh CD34(+) cells in all the three culture conditions at days 5, 10, and 14 of culture.

CONCLUSIONS

Expression of p15(INK4b) in HSCs was not decreased during ex vivo expansion. Also, no methylation of p15 promoter was observed, otherwise it would be capable of initiating some leukemic cell progression or disruption in hematopoietic regeneration.

p53-Independent, normal stem cell sparing epigenetic differentiation therapy for myeloid and other malignancies

Cytotoxic chemotherapy for acute myeloid leukemia (AML) usually produces only temporary remissions, at the cost of significant toxicity and risk for death. One fundamental reason for treatment failure is that it is designed to activate apoptosis genes (eg, TP53) that may be unavailable because of mutation or deletion. Unlike deletion of apoptosis genes, genes that mediate cell cycle exit by differentiation are present in myelodysplastic syndrome (MDS) and AML cells but are epigenetically repressed: MDS/AML cells express high levels of key lineage-specifying transcription factors. Mutations in these transcription factors (eg, CEBPA) or their cofactors (eg., RUNX1) affect transactivation function and produce epigenetic repression of late-differentiation genes that antagonize MYC. Importantly, this aberrant epigenetic repression can be redressed clinically by depleting DNA methyltransferase 1 (DNMT1, a central component of the epigenetic network that mediates transcription repression) using the deoxycytidine analogue decitabine at non-cytotoxic concentrations. The DNMT1 depletion is sufficient to trigger upregulation of late-differentiation genes and irreversible cell cycle exit by p53-independent differentiation mechanisms. Fortuitously, the same treatment maintains or increases self-renewal of normal hematopoietic stem cells, which do not express high levels of lineage-specifying transcription factors. The biological rationale for this approach to therapy appears to apply to cancers other than MDS/AML also. Decitabine or 5-azacytidine dose and schedule can be rationalized to emphasize this mechanism of action, as an alternative or complement to conventional apoptosis-based oncotherapy.

Knockdown of ZNF268, which is transcriptionally downregulated by GATA-1, promotes proliferation of K562 cells

The human ZNF268 gene encodes a typical KRAB-C2H2 zinc finger protein that may participate in hematopoiesis and leukemogenesis. A recent microarray study revealed that ZNF268 expression continuously decreases during erythropoiesis. However, the molecular mechanisms underlying regulation of ZNF268 during hematopoiesis are not well understood. Here we found that GATA-1, a master regulator of erythropoiesis, repressed the promoter activity and transcription of ZNF268. Electrophoretic mobility shift assays and chromatin immunoprecipitation assays showed that GATA-1 directly bound to a GATA binding site in the ZNF268 promoter in vitro and in vivo. Knockdown of ZNF268 in K562 erythroleukemia cells with specific siRNA accelerated cellular proliferation, suppressed apoptosis, and reduced expression of erythroid-specific developmental markers. It also promoted growth of subcutaneous K562-derived tumors in nude mice. These results suggest that ZNF268 is a crucial downstream target and effector of GATA-1. They also suggest the downregulation of ZNF268 by GATA-1 is important in promoting the growth and suppressing the differentiation of K562 erythroleukemia cells.

JmjC-domain containing histone demethylase 1B-mediated p15(Ink4b) suppression promotes the proliferation of leukemic progenitor cells through modulation of cell cycle progression in acute myeloid leukemia

The histone demethylase JHDM1B has been implicated in cell cycle regulation and tumorigenesis. In addition, it has been reported that JHDM1B is highly expressed in various human tumors, including leukemias. However, it is not clearly understood how JHDM1B contributes to acute myeloid leukemia (AML) cell proliferation. In this study, we investigated the cellular and molecular function of JHDM1B in AML cells. In AML cell lines and AML-derived ALDH(hi) (high aldehyde dehydrogenase activity)/CD34(+) cells, the levels of JHDM1B mRNA were significantly higher than in normal ALDH(hi) /CD34(+) cells. Reduction of JHDM1B expression in AML cells inhibited cell proliferation compared to control cells, through induction of G1 cell cycle arrest, an increase in the p15(Ink4b) mRNA and protein expression. JHDM1B mRNA was overexpressed in all 133 AML clinical specimens tested (n = 22, 57, 34, and 20 for M1, 2, 4, and 5 subtypes respectively). Compared to normal ALDH(hi) /CD34(+) cells, JHDM1B gene expression was 1.57- to 1.87-fold higher in AML-derived ALDH(hi) /CD34(+) cells. Moreover, the JHDM1B protein was more strongly expressed in AML-derived ALDH(hi) /CD34(+) cells from compared to normal ALDH(hi) /CD34(+) cells. In addition, depletion of JHDM1B reduced colony formation of AML-derived ALDH(hi) /CD34(+) cells due to induction of p15(Ink4b) expression through direct binding to p15(Ink4b) promoter and loss of demethylation of H3K36me2. In summary, we found that JHDM1B mRNA is predominantly expressed in AML-derived ALDH(hi) /CD34(+) cells, and that aberrant expression of JHDM1B induces AML cell proliferation through modulation of cell cycle progression. Thus, inhibition of JHDM1B expression represents an attractive target for AML therapy.

p53 independent epigenetic-differentiation treatment in xenotransplant models of acute myeloid leukemia

Suppression of apoptosis by TP53 mutation contributes to resistance of acute myeloid leukemia (AML) to conventional cytotoxic treatment. Using differentiation to induce irreversible cell cycle exit in AML cells could be a p53-independent treatment alternative, however, this possibility requires evaluation. In vitro and in vivo regimens of the deoxycytidine analogue decitabine that deplete the chromatin-modifying enzyme DNA methyl-transferase 1 without phosphorylating p53 or inducing early apoptosis were determined. These decitabine regimens but not equimolar DNA-damaging cytarabine upregulated the key late differentiation factors CCAAT enhancer-binding protein ɛ and p27/cyclin dependent kinase inhibitor 1B (CDKN1B), induced cellular differentiation and terminated AML cell cycle, even in cytarabine-resistant p53- and p16/CDKN2A-null AML cells. Leukemia initiation by xenotransplanted AML cells was abrogated but normal hematopoietic stem cell engraftment was preserved. In vivo, the low toxicity allowed frequent drug administration to increase exposure, an important consideration for S phase specific decitabine therapy. In xenotransplant models of p53-null and relapsed/refractory AML, the non-cytotoxic regimen significantly extended survival compared with conventional cytotoxic cytarabine. Modifying in vivo dose and schedule to emphasize this pathway of decitabine action can bypass a mechanism of resistance to standard therapy.

The specific linker phosphorylation of Smad2/3 indicates epithelial stem cells in stomach; particularly increasing in mucosae of Helicobacter-associated gastritis

BACKGROUND

The gastric corpus and antrum are believed to contain epithelial stem cells in the isthmus. However, the lack of useful markers has hindered studies of their origin. We explored whether Smad2/3, phosphorylated at specific linker threonine residues (pSmad2/3L-Thr), could serve as a marker for stem cells.

METHODS

Stomachs, small intestines, and colons from Helicobacter felis-infected and noninfected C57BL/6 mice were examined. Double immunofluorescent staining of pSmad2/3L-Thr with Ki67, cytokeratin 8, or doublecortin and calcium/calmodulin-dependent protein kinase-like-1 (DCAMKL1) was performed, and pSmad2/3L-Thr immunostaining-positive cells were counted. After immunofluorescent staining, we stained the same sections with hematoxylin-eosin and observed these cells under a light microscope.

RESULTS

In infected mice, pSmad2/3L-Thr immunostaining-positive cells were significantly increased in the corpus and antrum compared with those of noninfected mice (p < 0.0001). The number of Ki67 immunostaining-positive cells in the corpus and antrum of infected mice was also much greater than in the noninfected mice. Although pSmad2/3L-Thr immunostaining-positive cells were detected among the Ki67 cells, immunohistochemical co-localization of pSmad2/3L-Thr with Ki67 was never observed. pSmad2/3L-Thr immunostaining-positive cells showed immunohistochemical co-localization with cytokeratin 8, but some of them showed co-localization or adjacent localization with DCAMKL1 immunostaining-positive cells. Under a light microscope, pSmad2/3L-Thr immunostaining-positive cells indicated undifferentiated morphological features and were confirmed in the isthmus. In small intestines and colons, pSmad2/3L-Thr immunostaining-positive cells were detected in specific epithelial cells around crypt bases, where the respective putative stem cells are thought to exist.

CONCLUSIONS

We have identified the significant expression of pSmad2/3L-Thr in specific epithelial cells of the murine stomach and have suggested these cells to be epithelial stem cells.

RNA interference reveals a requirement for both p18INK4c and p27Kip1 in B lymphopoiesis

Cyclin-dependent kinase inhibitors (CKIs) p18(INK4c) (p18) and p27(Kip1) (p27) were reported to be able to modulate self-renewal and differentiation of hematopoietic stem cells (HSCs) and hematopoietic progenitor cells, and regulate the lineage cell proliferation and maturation into the terminal elements; however, whether p18 and p27 in HSCs affect the development of lineage cells, especially B lymphocytes, in the reconstituted blood is unknown. Here we employed small-interference RNA (siRNA) technique, which provides a powerful tool for tissue-targeted knockdown of genes, to evaluate the biological functions of the p18 and p27 in the hematopoiesis process. We knocked down the expression of p18, p27 alone or both in the isolated sca-1(+) bone marrow cells by lentiviral vector-based siRNA system, and transplanted these cells into lethally irradiated C57BL/6J mice to evaluate the effect of these two genes on reconstituted lymphocyte development. The knockdown of p18 or p27 alone or both was proved to be effective as verified by western blotting. FACS analysis results showed that compared with the control group, the B lymphocytes were both significantly lower in p18, p27 alone and especially in both p18 and p27 knockdown group in reconstituted peripheral blood; and the B lymphocytes showed similar trend in bone marrow. Interestingly, the differentiation to T cells was not greatly changed, only with the dramatic decrease of the CD4/CD8 ratio. Overexpression of the antiapoptotic protein Bcl2 could not rescue the B lymphopoiesis. All these results demonstrate that p18 and p27 are collaboratively involved in B lymphopoiesis, and simultaneous knockdown of p18 and p27 probably blocks the differentiation from HSCs to B lymphocytes, but not triggers apoptosis of B cell precursors.

Two cyclin-dependent kinase pathways are essential for polarized trafficking of presynaptic components

Polarized trafficking of synaptic proteins to axons and dendrites is crucial to neuronal function. Through forward genetic analysis in C. elegans, we identified a cyclin (CYY-1) and a cyclin-dependent Pctaire kinase (PCT-1) necessary for targeting presynaptic components to the axon. Another cyclin-dependent kinase, CDK-5, and its activator p35, act in parallel to and partially redundantly with the CYY-1/PCT-1 pathway. Synaptic vesicles and active zone proteins mostly mislocalize to dendrites in animals defective for both PCT-1 and CDK-5 pathways. Unlike the kinesin-3 motor, unc-104/Kif1a mutant, cyy-1 cdk-5 double mutants have no reduction in anterogradely moving synaptic vesicle precursors (SVPs) as observed by dynamic imaging. Instead, the number of retrogradely moving SVPs is dramatically increased. Furthermore, this mislocalization defect is suppressed by disrupting the retrograde motor, the cytoplasmic dynein complex. Thus, PCT-1 and CDK-5 pathways direct polarized trafficking of presynaptic components by inhibiting dynein-mediated retrograde transport and setting the balance between anterograde and retrograde motors.

Histone deacetylases are critical targets of bortezomib-induced cytotoxicity in multiple myeloma

Bortezomib is now widely used for the treatment of multiple myeloma (MM); however, its action mechanisms are not fully understood. Despite the initial results, recent investigations have indicated that bortezomib does not inactivate nuclear factor-kappaB activity in MM cells, suggesting the presence of other critical pathways leading to cytotoxicity. In this study, we show that histone deacetylases (HDACs) are critical targets of bortezomib, which specifically down-regulated the expression of class I HDACs (HDAC1, HDAC2, and HDAC3) in MM cell lines and primary MM cells at the transcriptional level, accompanied by reciprocal histone hyperacetylation. Transcriptional repression of HDACs was mediated by caspase-8-dependent degradation of Sp1 protein, the most potent transactivator of class I HDAC genes. Short-interfering RNA-mediated knockdown of HDAC1 enhanced bortezomib-induced apoptosis and histone hyperacetylation, whereas HDAC1 overexpression inhibited them. HDAC1 overexpression conferred resistance to bortezomib in MM cells, and administration of the HDAC inhibitor romidepsin restored sensitivity to bortezomib in HDAC1-overexpressing cells both in vitro and in vivo. These results suggest that bortezomib targets HDACs via distinct mechanisms from conventional HDAC inhibitors. Our findings provide a novel molecular basis and rationale for the use of bortezomib in MM treatment.

Gli1 regulates the proliferation and differentiation of HSCs and myeloid progenitors

The Hedgehog (Hh) pathway is essential for normal embryonic development and tissue repair. The role of Hh signaling in hematopoiesis has been studied primarily by modulating the activity of Patched and Smoothened, but results have been conflicting. Some studies demonstrate a requirement for pathway activity in hematopoiesis, whereas others report that it is dispensable. Hh activity converges on the Gli transcription factors, but the specific role of these downstream effectors in hematopoiesis has not been reported. We have analyzed hematopoietic stem cell (HSC) and progenitor function in mice with a homozygous deletion of Gli1 (Gli1(null)). Gli1(null) mice have more long-term HSCs that are more quiescent and show increased engraftment after transplantation. In contrast, myeloid development is adversely affected with decreased in vitro colony formation, decreased in vivo response to granulocyte colony-stimulating factor (G-CSF), and impaired leukocyte recovery after chemotherapy. Levels of the proto-oncogene Cyclin D1 are reduced in Gli1(null) mice and may explain the loss of proliferation seen in HSCs and progenitor cells. These data demonstrate that Gli1 regulates normal and stress hematopoiesis. Moreover, they suggest that Gli1 and Smoothened may not be functionally redundant, and direct GLI1 inhibitors may be needed to effectively block HH/GLI1 activity in human disease.

Expression levels of histone deacetylases determine the cell fate of hematopoietic progenitors

Histone deacetylases (HDACs) are globally implicated in the growth and differentiation of mammalian cells; however, relatively little is known about their specific roles in hematopoiesis. In this study, we investigated the expression of HDACs in human hematopoietic cells and their functions during hematopoiesis. The expression of HDACs was very low in hematopoietic progenitor cells, which was accompanied by histone hyperacetylation. HDACs were detectable in more differentiated progenitors and erythroid precursors but down-regulated in mature myeloid cells especially granulocytes. In contrast, acute myeloid leukemias showed HDAC overexpression and histone hypoacetylation. Transcription of the HDAC1 gene was repressed by CCAAT/enhancer binding proteins during myeloid differentiation, and activated by GATA-1 during erythro-megakaryocytic differentiation. Small interfering RNA-mediated knockdown of HDAC1 enhanced myeloid differentiation in immature hematopoietic cell lines and perturbed erythroid differentiation in progenitor cells. Myeloid but not erythro-megakaryocytic differentiation was blocked in mice transplanted with HDAC1-overexpressing hematopoietic progenitor cells. These findings suggest that HDAC is not merely an auxiliary factor of genetic elements but plays a direct role in the cell fate decision of hematopoietic progenitors.

Tight control of MEK-ERK activation is essential in regulating proliferation, survival, and cytokine production of CD34+-derived neutrophil progenitors

A plethora of extracellular stimuli regulate growth, survival, and differentiation responses through activation of the MEK-ERK MAPK signaling module. Using CD34+ hematopoietic progenitor cells, we describe a novel role for the MEK-ERK signaling module in the regulation of proliferation, survival, and cytokine production during neutrophil differentiation. Addition of the specific MEK1/2 inhibitor U0126 resulted in decreased proliferation of neutrophil progenitors. Conversely, transient activation of a conditionally active MEK1 mutant resulted in the expansion of progenitor cells, which thereafter differentiated normally into mature neutrophils. In contrast, chronic MEK1 activation was found to induce cell death of CD34+ neutrophil progenitors. Microarray analysis of CD34+ progenitor cells showed that activation of MEK1 resulted in changes in expression of a variety of cell-cycle modulating genes. Furthermore, conditional activation of MEK1 resulted in a dramatic increase in the expression of mRNA transcripts encoding a large number of hematopoietic cytokines, chemokines, and growth factors. These findings identify a novel role for MEK-ERK signaling in regulating the balance between proliferation and apoptosis during neutrophil differentiation, and they suggest the need for tight control of MEK-ERK activation to prevent the development of bone marrow failure.

Silencing of membrane-associated sialidase Neu3 diminishes apoptosis resistance and triggers megakaryocytic differentiation of chronic myeloid leukemic cells K562 through the increase of ganglioside GM3

In chronic myeloid leukemia K562 cells, differentiation is also blocked because of low levels of ganglioside GM3, derived by the high expression of sialidase Neu3 active on GM3. In this article, we studied the effects of Neu3 silencing (40-70% and 63-93% decrease in protein content and activity, respectively) in these cells. The effects were as follows: (a) gangliosides GM3, GM1, and sialosylnorhexaosylceramide increased markedly; (b) cell growth and [(3)H]thymidine incorporation diminished relevantly; (c) as mRNA, cyclin D2, and Myc were much less expressed, whereas cyclin D1 was expressed more like its inhibitor p21; (d) as mRNA, pro-apoptotic proteins Bax and Bad increased with concurrent decrease and increase in the anti-apoptotic proteins Bcl-2 and Bcl-XL, respectively; (e) the apoptosis inducers etoposide and staurosporine were active on Neu3 silencing cells but not on mock cells; (f) as mRNA, the megakaryocytic markers CD10, CD44, CD41, and CD61 increased similar to the case of mock cells stimulated with PMA; (g) the signaling cascades mediated by PLC-beta2, PKC, RAF, ERK1/2, RSK90, and JNK were largely activated. The induction of a GM3-rich ganglioside pattern in K562 cells by treatment with brefeldin A elicited a phenotype similar to that of Neu3 silencing cells. In conclusion, upon Neu3 silencing, K562 cells show a decrease in proliferation, propensity to undergo apoptosis, and megakaryocytic differentiation.

p15Ink4b: dual function in myelopoiesis and inactivation in myeloid disease

p15Ink4b (p15) is a cyclin-dependent kinase inhibitor (CDKI) that is known for arresting the cell cycle in early G1 phase by inhibiting the activation of cyclin dependent kinases 4 and 6. Loss of p15 expression has been associated with several cancer types but its silencing is frequent in acute myeloid leukemia (AML) and myeloid dysplastic syndrome (MDS). Several mechanisms have been identified that are responsible for silencing the gene encoding p15 in myeloid disease, including gene hypermethylation, transcription factor deregulation and direct inhibition by translocation products. The effect of p15 loss during disease may be attributed to the dual role of this protein as a mediator of cell cycle arrest in late stage myeloid progenitors and as a regulator of differentiation in early common myeloid progenitors (CMP). Here we outline the mechanisms by which p15 is silenced and the functions of this CDKI in myelopoiesis as well as discuss the implications of these findings to myeloid disease.

P19INK4D links endomitotic arrest and megakaryocyte maturation and is regulated by AML-1

The molecular mechanisms that regulate megakaryocyte (MK) ploidization are poorly understood. Using MK differentiation from primary human CD34(+) cells, we observed that p19(INK4D) expression was increased both at the mRNA and protein levels during ploidization. p19(INK4D) knockdown led to a moderate increase (31.7% +/- 5%) in the mean ploidy of MKs suggesting a role of p19(INK4D) in the endomitotic arrest. This increase in ploidy was associated with a decrease in the more mature MK population (CD41(high)CD42(high)) at day 9 of culture, which was related to a delay in differentiation. Inversely, p19(INK4D) overexpression in CD34(+) cells resulted in a decrease in mean ploidy level associated with an increase in CD41 and CD42 expression in each ploidy class. Confirming these in vitro results, bone marrow MKs from p19(INK4D) KO mice exhibited an increase in mean ploidy level from 18.7N (+/- 0.58N) to 52.7N (+/- 12.3N). Chromatin immunoprecipitation assays performed in human MKs revealed that AML-1 binds in vivo the p19(INK4D) promoter. Moreover, AML-1 inhibition led to the p19(INK4D) down-regulation in human MKs. These results may explain the molecular link at the transcriptional level between the arrest of endomitosis and the acceleration of MK differentiation.

The role of peroxiredoxin III on late stage of proerythrocyte differentiation

Peroxiredoxin III (Prdx III), the mitochondrial peroxidase, was preferentially expressed in murine erythroleukemia (MEL) cells. However, the mechanisms by which Prdx III regulates erythroid differentiation are unknown. In this study, K562 cells were differentiated by Ara-C treatment, and Prdx III was dramatically increased until day 5. We also investigated Prdx III expression pattern on in vitro erythropoiesis of human CD34(+) cells. When human CD34(+) cells became proerythrocyte on day 7, Prdx III was diminished, and then augmented on day 12. We established the stable sublines of Prdx III overexpression (O/E), and dominant-negative (D/N). The intracellular ROS level of Prdx III O/E cell line was lower than D/N stable cell lines. Moreover, Prdx III O/E cell line was placed in G1-arrest, but not D/N cell lines. Finally, the expression level of beta-globin and GATA-1 was dramatically increased in Prdx III O/E cell line.

E2F-6 suppresses growth-associated apoptosis of human hematopoietic progenitor cells by counteracting proapoptotic activity of E2F-1

E2F-6 is a dominant-negative transcriptional repressor against other members of the E2F family. In this study, we investigated the expression and function of E2F-6 in human hematopoietic progenitor cells to clarify its role in hematopoiesis. We found that among E2F subunits, E2F-1, E2F-2, E2F-4, and E2F-6 were expressed in CD34(+) human hematopoietic progenitor cells. The expression of E2F-6 increased along with proliferation and decreased during differentiation of hematopoietic progenitors, whereas the other three species were upregulated in CD34(-) bone marrow mononuclear cells. Overexpression of E2F-6 did not affect the growth of immature hematopoietic cell line K562 but suppressed E2F-1-induced apoptosis, whereas it failed to inhibit apoptosis induced by differentiation inducers and anticancer drugs. Among E2F-1-dependent apoptosis-related molecules, E2F-6 specifically inhibited upregulation of Apaf-1 by competing with E2F-1 for promoter binding. E2F-6 similarly suppressed apoptosis and Apaf-1 upregulation in primary hematopoietic progenitor cells during cytokine-induced proliferation but had no effect when they were differentiated. As a result, E2F-6 enhanced the clonogenic growth of colony-forming unit-granulocyte, erythroid, macrophage, and megakaryocyte. These results suggest that E2F-6 provides a failsafe mechanism against loss of hematopoietic progenitor cells during proliferation. Disclosure of potential conflicts of interest is found at the end of this article.

Cyclin D-Cdk4 is regulated by GATA-1 and required for megakaryocyte growth and polyploidization

Endomitosis is a unique form of cell cycle used by megakaryocytes, in which the latter stages of mitosis are bypassed so that the cell can increase its DNA content and size. Although several transcription factors, including GATA-1 and RUNX-1, have been implicated in this process, the link between transcription factors and polyploidization remains undefined. Here we show that GATA-1-deficient megakaryocytes, which display reduced size and polyploidization, express nearly 10-fold less cyclin D1 and 10-fold increased levels of p16 compared with their wild-type counterparts. We further demonstrate that cyclin D1 is a direct GATA-1 target in megakaryocytes, but not erythroid cells. Restoration of cyclin D1 expression, when accompanied by ectopic overexpression of its partner Cdk4, resulted in a dramatic increase in megakaryocyte size and DNA content. However, terminal differentiation was not rescued. Of note, polyploidization was only modestly reduced in cyclin D1-deficient mice, likely due to compensation by elevated cyclin D3 expression. Finally, consistent with an additional defect conferred by increased levels of p16, inhibition of cyclin D-Cdk4 complexes with a TAT-p16 fusion peptide significantly blocked polyploidization of wild-type megakaryocytes. Together, these data show that GATA-1 controls growth and polyploidization by regulating cyclin D-Cdk4 kinase activity.

Promiscuous and lineage-specific roles of cell cycle regulators in haematopoiesis

Haematopoietic cell number is maintained by a delicate balance between cell proliferation, differentiation and death. Gene knockout studies in mice have revealed the complex roles of cyclins, CDKs, and CDK inhibitors in regulating cell proliferation and differentiation in the haematopoietic system. These studies point to families of cell cycle regulators which display both redundant and unique roles within a lineage and developmental-stage specific manner. Moreover, the promiscuity of these cell cycle regulators is critical for haematopoietic cell proliferation and differentiation. In this review, we discuss the current evidence from mouse models that the complexity and multifarious nature of the haematopoietic system is critical for its form and function.

Vitamin A potentiates CpG-mediated memory B-cell proliferation and differentiation: involvement of early activation of p38MAPK

Foreign CpG-DNA from viruses and bacteria can activate memory B cells through binding to toll-like receptor 9, and this pathway has been hypothesized to be involved in the continuous activation of memory B cells ensuring life-long humoral immunity. In this study, we demonstrate that retinoic acid (RA) is a potent coactivator of this pathway in human B cells. RA enhanced the CpG-mediated proliferation of CD27(+) memory B cells, and the proliferative response was accompanied by increased immunoglobulin (Ig) secretion indicative of plasma-cell formation. The RA-induced proliferation was preceded by enhanced expression of cyclin D3, and both the expression of cyclin D3 and the induced Ig secretion were found to be dependent on IL-10. Of importance, RA increased the CpG-induced phosphorylation of ERK1/2, p38MAPK, and IkappaB as early as 30 minutes after stimulation. By using specific inhibitors, all the RA-mediated events, including proliferation, cyclin D3 expression, IL-10 secretion, and Ig secretion, were shown to be dependent on p38MAPK. Hence, we propose that RA can strengthen humoral immunity by promoting CpG-mediated stimulation of CD27(+) B cells via activation of p38MAPK resulting in increased proliferation and differentiation to Ig-secreting plasma cells.

Expression analyses and transcriptional regulation of mouse nucleolar spindle-associated protein gene in erythroid cells: essential role of NF-Y

Nucleolar spindle-associated protein (NuSAP), a recently characterised microtubule-associated protein, appears to participate in cell cycle regulation. It has been demonstrated that NuSAP is expressed preferentially in the erythroid lineage in haematopoietic cells. To characterise its role in erythropoiesis, we examined the expression profile of the NuSAP gene. In fractionated murine erythroblasts, NuSAP mRNA was remarkably more abundant in the subset corresponding to immature erythroblasts (TER119(+)CD71(high)) than mature erythroblasts (TER119(+)CD71(low)), and it was significantly increased in TER119(+) cells from in vivo phlebotomised mice compared with control mice. Furthermore, during erythroid maturation of mouse erythroleukaemia (MEL) cells by dimethylsulfoxide, NuSAP mRNA was increased at 24-72 h. These results suggested that the NuSAP gene might contribute to the expansion of immature erythroblast pool. The regulatory mechanism of NuSAP gene was investigated using MEL cells. Sequence analysis revealed that NuSAP promoter has four CCAAT boxes, an Sp1 element, a GATA-like element, a CACCC element, a Myb element and lacks a TATA box. Promoter analyses demonstrated that duplicated CCAAT boxes located at -81/-85 and -30/-34 were essential for promoter activity. Furthermore, the promoter was trans-activated by NF-YA through these elements. These results suggest that NuSAP might play an important role in erythroid proliferation under the control of NF-Y.

Promoter SNPs in G1/S checkpoint regulators and their impact on the susceptibility to childhood leukemia

Mutations leading to the alteration of cell-cycle checkpoint functions are a common feature of most cancers. Because of the highly regulated nature of the cell cycle, it seems likely that variation in gene dosage of key components due to functional regulatory polymorphisms could play an important role in cancer development. Here we provide evidence of the involvement of promoter single-nucleotide polymorphisms (pSNPs) in the cyclin-dependent–kinase inhibitor genes CDKN2A, CDKN2B, CDKN1A, and CDKN1B in the etiology of childhood pre-B acute lymphoblastic leukemia (ALL). A case-control study, conducted in 240 patients with pre-B ALL and 277 healthy controls, combined with a family-based analysis using 135 parental trios, all of French-Canadian origin, were used to evaluate single-site genotypic as well as multilocus haplotypic associations for a total of 10 pSNPs. Using both study designs, we showed evidence of association between variants CDKN2A −222A, CDKN2B −593A, and CDKN1B −1608A, and an increased risk of ALL. These findings suggest that variable expression levels of cell-cycle inhibitor genes CDKN2A, CDKN2B, and CDKN1B due to regulatory polymorphisms could indeed influence the risk of childhood pre-B ALL and contribute to carcinogenesis.

Effects of 5-aza-2'-deoxycytidine on proliferation, differentiation and p15/INK4b regulation of human hematopoietic progenitor cells

The demethylating agents 5-azacytidine and 5-aza-2'-deoxycytidine (DAC) have been shown to induce differentiation and inhibit growth of leukemic myeloid cells at low concentrations. However, the effect of DAC in changing the differentiation and proliferation behavior of normal human myeloid progenitors has rarely been investigated. Therefore, we established an in vitro model of normal hematopoietic differentiation, using CD34+ cells from mobilized peripheral blood, to study proliferation and colony formation, expression of several myeloid maturation markers and of the inhibitor of cyclin-dependent kinases p15/INK4b. Upon DAC treatment, cell growth was significantly decreased in a dose-dependent manner, without an increase in cytotoxicity. DAC treatment also resulted in a substantial increase of lysozyme-positive cells, which could be enhanced by G-CSF, a modest increase of myeloperoxidase+ and CD15+ cells, as well as an increase of colony-forming cells (CFU-GM) compared to control cells. p15/INK4b protein expression was strongly upregulated upon myeloid maturation, and additional DAC treatment did not change p15 expression or the methylation status of the p15 promoter at the noncytotoxic concentrations used. Taken together, these data indicate a role of DAC in changing myeloid progenitor cell expansion and differentiation. This model appears suitable also for global analyses of multiple differentially methylated genes.

Inhibition of TPO-induced MEK or mTOR activity induces opposite effects on the ploidy of human differentiating megakaryocytes

The megakaryocyte is a paradigm for mammalian polyploid cells. However, the mechanisms underlying megakaryocytic polyploidization have not been elucidated. In this study, we investigated the role of Shc-Ras-MAPK and PI3K-AKT-mTOR pathways in promoting megakaryocytic differentiation, maturation and polyploidization. CD34+ cells, purified from human peripheral blood, were induced in serum-free liquid suspension culture supplemented with thrombopoietin (TPO) to differentiate into a virtually pure megakaryocytic progeny (97-99% CD61+/CD41+ cells). The early and repeated addition to cell cultures of low concentrations of PD98059, an inhibitor of MEK1/2 activation, gave rise to a population of large megakaryocytes showing an increase in DNA content and polylobated nuclei (from 45% to 70% in control and treated cultures, respectively). Conversely, treatment with the mTOR inhibitor rapamycin strongly inhibited cell polyploidization, as compared with control cultures. Western blot analysis of PD98059-treated progenitor cells compared with the control showed a downmodulation of phospho-ERK 1 and phospho-ERK 2 and a minimal influence on p70S6K activation; by contrast, p70S6K activation was completely inhibited in rapamycin-treated cells. Interestingly, the cyclin D3 localization was nuclear in PD98059-induced polyploid megakaryocytes, whereas it was completely cytoplasmic in those treated with rapamycin. Altogether, our results are in line with a model in which binding of TPO to the TPO receptor (mpl) could activate the rapamycin-sensitive PI3K-AKT-mTOR-p70S6K pathway and its downstream targets in promoting megakaryocytic cell polyploidization.

Cyclin D3 promotes adipogenesis through activation of peroxisome proliferator-activated receptor gamma

In addition to their role in cell cycle progression, new data reveal an emerging role of D-type cyclins in transcriptional regulation and cellular differentiation processes. Using 3T3-L1 cell lines to study adipogenesis, we observed an up-regulation of cyclin D3 expression throughout the differentiation process. Surprisingly, cyclin D3 was only minimally expressed during the initial stages of adipogenesis, when mitotic division is prevalent. This seemingly paradoxical expression led us to investigate a potential cell cycle-independent role for cyclin D3 during adipogenesis. We show here a direct interaction between cyclin D3 and the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma). Our experiments reveal cyclin D3 acts as a ligand-dependent PPARgamma coactivator, which, together with its cyclin-dependent kinase partner, phosphorylates the A-B domain of the nuclear receptor. Overexpression and knockdown studies with cyclin D3 had marked effects on PPARgamma activity and subsequently on adipogenesis. Chromatin immunoprecipitation assays confirm the participation of cyclin D3 in the regulation of PPARgamma target genes. We show that cyclin D3 mutant mice are protected from diet-induced obesity, display smaller adipocytes, have reduced adipogenic gene expression, and are insulin sensitive. Our results indicate that cyclin D3 is an important factor governing adipogenesis and obesity.

Methylation silencing of the Apaf-1 gene in acute leukemia

Apaf-1 is important for tumor suppression and drug resistance because it plays a central role in DNA damage-induced apoptosis. Inactivation of the Apaf-1 gene is implicated in disease progression and chemoresistance of some malignancies. In this study, we attempted to clarify the role of Apaf-1 in leukemogenesis. Apaf-1 mRNA levels were below the detection limit or very low in 5 of 20 human leukemia cell lines (25%) and 5 of 12 primary acute myeloblastic leukemia cells (42%). There were no gross structural abnormalities in the Apaf-1 gene in these samples. Expression of factors regulating Apaf-1 transcription, such as E2F-1, p53, and Sp-1, did not differ between Apaf-1-positive and Apaf-1-negative cells. Methylation of CpG in the region between +87 and +128 of the Apaf-1 gene was almost exclusively observed in Apaf-1-defective cell lines. Treatment of these cells with 5-aza-2'-deoxycytidine, a specific inhibitor of DNA methylation, restored the expression of Apaf-1. Furthermore, we showed that the region between +87 and +128 could act as a repressor element by recruiting corepressors such as methylated DNA-binding domain 2 and histone deacetylase 1 upon methylation. Overexpression of Dnmt1, a mammalian maintenance DNA methyltransferase, was associated with Apaf-1 gene methylation. DNAs from Dnmt1-overexpressing cells were more resistant to digestion with methylation-sensitive enzyme HpaII than those from cells with low Dnmt1 expression, suggesting that Dnmt1 mediates aberrant methylation of multiple genes. In conclusion, methylation silencing is a mechanism of the inactivation of Apaf-1 in acute leukemia, and Dnmt1 overexpression may underlie hypermethylation of the Apaf-1 gene.

MicroRNA modulation of megakaryoblast fate involves cholinergic signaling

MicroRNAs (miRNAs) are abundant small regulatory RNAs with multiple roles in cell fate determination. The processes regulating cellular miRNA levels are still unclear and experimental oligonucleotide tools to readily mimic their effects are not yet available. Here, we report that thapsigargin-induced intracellular Ca(++) release suppressed pre-miR-181a levels in human promegakaryotic Meg-01 cells, induced differentiation-associated nuclear endoreduplication and caspase-3 activation and replaced the acetylcholinesterase 3' splice variant AChE-S with AChE-R. AChE, PKC and PKA inhibitors all attenuated the pre-miR-181a decline and the induced differentiation. AChmiON, a synthetic 23-mer 2'-oxymethylated oligonucleotide mimicking the miR-181a sequence, blocked the calcium-induced differentiation while elevating cellular pre-miR-181a levels and inducing DNA fragmentation and cell death. Moreover, when added to RW 264.7 macrophages, AChmiON at 100 nM induced nitric oxide production with efficiency close to that of bacterial endotoxin, demonstrating physiologically relevant activities also in blood-born monocytes/macrophages. The stress-induced modulation of hematopoietic miR-181a levels through AChE, PKC and PKA cascade(s) suggests using miRNA mimics for diverting the fate of hematopoietic tumor cells towards differentiation and/or apoptosis.

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.

Hematopoietic malignancies associated with increased Stat5 and Bcl-xL expressions in Ink4a/Arf-deficient mice

The INK4a/ARF locus, which encodes the two distinct proteins p16(INK4a) and p14(ARF), is frequently altered in various hematological malignancies as well as in other types of cancers in humans. In this study, we surveyed tumors that had spontaneously developed in Ink4a/Arf-deficient mice with an inbred FVB/NJ genetic background. We found that an Ink4a/Arf-deficiency exerted more severe effects on the induction of hematopoietic malignancies in mice with an inbred FVB/NJ genetic background than in mice with a mixed genetic background. We also provided the evidence that this prevalence of hematopoietic malignancies in Ink4a/Arf-deficient mice is associated with the upregulated expressions of Stat5 and its transcriptional target, Bcl-x(L), both of which are involved in the regulation of hematopoiesis. These results suggest a possible implication of the Ink4a/Arf locus in the control of hematopoietic pathways by negatively regulating the Stat5-signalling pathways.

Androgen Regulation of Stage-Dependent Cyclin D2 Expression in Sertoli Cells Suggests a Role in Modulating Androgen Action on Spermatogenesis1

Regulation of spermatogenesis involves stage-dependent androgen action on Sertoli cells, but the pathways involved are unclear. We assessed if cyclin D2 could play a role. In rats, Sertoli cell nuclear, stage-dependent immunoexpression of cyclin D2 switched on after Day 10 and persisted through Day 35, but disappeared by adulthood. However, ethane dimethane sulfonate (EDS)-induced testosterone withdrawal in adult rats for 6 days induced stage-dependent cyclin D2 immunoexpression in Sertoli cells, with highest expression at stages IX-XII and nondetectable at stages VI-VIII (opposite that for androgen receptor [AR] immunoexpression). In EDS-treated rats, a single injection of testosterone but not of estrogen reversed this change in 4 h, and testosterone administration from the time of EDS treatment prevented expression of cyclin D2 in Sertoli cells. The EDS-induced changes in cyclin D2 immunoexpression were matched by changes in expression of Ccnd2 (cyclin D2) mRNA in isolated stage-dissected tubules. Treatment of adult rats with flutamide induced stage-dependent cyclin D2 immunoexpression in Sertoli cells within 18 h, and confocal microscopy revealed that immunoexpression of AR and cyclin D2 were mutually exclusive within individual seminiferous tubules in these animals. Sertoli cell-selective ablation of the AR in mice using Cre/loxP technology also resulted in stage-dependent Sertoli cell cyclin D2 immunoexpression. Downstream from cyclin D2 action is retinoblastoma 1 (RB1), a tumor suppressor protein, immunoexpression of which paralleled stage-dependent AR expression in Sertoli cells; RB1 stage specificity disappeared after EDS treatment. These results point to a non-cell cycle role for cyclin D2 and RB1 in mature Sertoli cells in the stage-dependent mechanisms regulated by AR expression and androgen action.

Menin and MLL cooperatively regulate expression of cyclin-dependent kinase inhibitors

Mutations in the MEN1 gene are associated with the multiple endocrine neoplasia syndrome type 1 (MEN1), which is characterized by parathyroid hyperplasia and tumors of the pituitary and pancreatic islets. The mechanism by which MEN1 acts as a tumor suppressor is unclear. We have recently shown that menin, the MEN1 protein product, interacts with mixed lineage leukemia (MLL) family proteins in a histone methyltransferase complex including Ash2, Rbbp5, and WDR5. Here, we show that menin directly regulates expression of the cyclin-dependent kinase inhibitors p27Kip1 and p18Ink4c. Menin activates transcription by means of a mechanism involving recruitment of MLL to the p27Kip1 and p18Ink4c promoters and coding regions. Loss of function of either MLL or menin results in down-regulation of p27Kip1 and p18Ink4c expression and deregulated cell growth. These findings suggest that regulation of cyclin-dependent kinase inhibitor transcription by cooperative interaction between menin and MLL plays a central role in menin's activity as a tumor suppressor.

Ectopic cyclin D1 expression blocks STI571-induced erythroid differentiation of K562 cells

Bcr-Abl tyrosine kinase inhibitor induces apoptosis and erythroid differentiation of K562 cells. During this erythroid differentiation, c-Myc and cyclin D1 transcripts are transiently downregulated. Accordingly, we studied the effect of cyclin D1 overexpression on erythroid differentiation. After treatment with 250 nM STI571, 90% of K562 and 25% of K562/D1 cells underwent erythroid differentiation. The basal expression of glycophorin A in K562/D1 cells was markedly diminished compared with that by parental cells. STI571 treatment failed to induce glycophorin A expression in K562/D1 cells. During STI571 treatment, ERK activity was downregulated in parental cells, while it was constantly activated in K562/D1 cells. These results suggest that ectopic expression of cyclin D1 causes the resistance of K562 cells to erythroid differentiation by modulating ERK regulation.