Differentiation Of Human Leukemia Cells Research Articles

Pharmacological targeting of CBX7 alters the epigenetic landscape and induces differentiation of leukemic cells

AbstractSelf-renewal of leukemic cells results in the accumulation of dysfunctional blood cells and suppression of normal hematopoiesis. The polycomb group protein chromobox 7 (CBX7) is an epigenetic regulator that represses genes required for differentiation and cell cycle arrest and thereby promotes self-renewal. Because leukemic cells are highly self-renewing, we tested whether pharmacological targeting of CBX7 would reduce self-renewal and induce differentiation of human leukemic cells. We found that existing and newly developed CBX7 inhibitors derepress the epigenome, resulting in reduced ubiquitination of histone 2A and reduced binding of CBX7 to its target genes. This led to reduced cell growth, increased differentiation of leukemic cells in vitro, and delayed engraftment of primary leukemic cells in xenotransplant models. Therefore, pharmacological targeting of CBX7 constitutes a novel therapeutic approach for leukemia.

Generation of a new therapeutic d-peptide that induces the differentiation of acute myeloid leukemia cells through A TLR-2 signaling pathway

Acute myeloid leukemia (AML) is caused by clonal disorders of hematopoietic stem cells. Differentiation therapy is emerging as an important treatment modality for leukemia, given its less toxicity and wider applicable population, but the arsenal of differentiation-inducing agents is still very limited. In this study, we adapted a competitive peptide phage display platform to search for candidate peptides that could functionally induce human leukemia cell differentiation. A monoclonal phage (P6) and the corresponding peptide (pep-P6) were identified. Both l- and d-chirality of pep-P6 showed potent efficiency in inducing AML cell line differentiation, driving their morphologic maturation and upregulating the expression of macrophage markers and cytokines, including CD11b, CD14, IL-6, IL-1β, and TNF-α. In the THP-1 xenograft animal model, administration of d-pep-P6 was effective in inhibiting disease progression. Importantly, exposure to d-pep-P6 induced the differentiation of primary human leukemia cells isolated AML patients in a similar manner to the AML cell lines. Further mechanism study suggested that d-pep-P6 induced human leukemia cell differentiation by directly activating a TLR-2 signaling pathway. These findings identify a novel d-peptide that may promote leukemia differentiation therapy.

Tumor necrosis factor‑related apoptosis‑inducing ligand is a novel transcriptional target of runt‑related transcription factor1.

Runt-related transcription factor 1 (RUNX1), which is also known as acute myeloid leukemia 1 (AML1), has been frequently found with genomic aberrations in human leukemia. RUNX1 encodes a transcription factor that can regulate the expression of hematopoietic genes. In addition, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) performs an important function for malignant tumors in immune surveillance. However, the regulatory mechanism of TRAIL expression remain to be fully elucidated. In the present study, tetradecanoylphorbol 13-acetate-treated megakaryocytic differentiated K562 cells was used to examine the effect of RUNX1 on TRAIL expression. Luciferase assay series of TRAIL promoters for the cells co-transfected with RUNX1 and core-binding factor β (CBFβ) expression vectors were performed to evaluate the nature of TRAIL transcriptional regulation. Electrophoresis mobility shift assay of the RUNX1 consensus sequence of the TRAIL promoter with recombinant RUNX1 and CBFβ proteins was also performed. BloodSpot database analysis for TRAIL expression in patients with acute myeloid leukemia were performed. The expression of TRAIL, its receptor Death receptor 4 and 5 and RUNX1 in K562 cells transfected with the RUNX1 expression vector and RUNX1 siRNA were evaluated by reverse transcription-quantitative PCR (RT-qPCR). TRAIL and RUNX1-ETO expression was also measured in Kasumi-1 cells transfected with RUNX1-ETO siRNA and in KG-1 cells transfected with RUNX1-ETO expression plasmid, both by RT-qPCR. Cell counting, lactate dehydrogenase assay and cell cycle analysis by flow cytometry were performed on Kasumi-1, KG-1, SKNO-1 and K562 cells treated with TRAIL and HDAC inhibitors sodium butyrate or valproic acid. The present study demonstrated that RUNX1 is a transcriptional regulator of TRAIL. It was initially found that the induction of TRAIL expression following the megakaryocytic differentiation of human leukemia cells was RUNX1-dependent. Subsequently, overexpression of RUNX1 was found to increase TRAIL mRNA expression by activating its promoter activity. Additional analyses revealed that RUNX1 regulated the expression of TRAIL in an indirect manner, because RUNX1 retained its ability to activate this promoter following the mutation of all possible RUNX1 consensus sites. Furthermore, TRAIL expression was reduced in leukemia cells carrying the t(8;21) translocation, where the RUNX1-ETO chimeric protein interfere with normal RUNX1 function. Exogenous treatment of recombinant TRAIL proteins was found to induce leukemia cell death. To conclude, the present study provided a novel mechanism, whereby TRAIL is a target gene of RUNX1 and TRAIL expression was inhibited by RUNX1-ETO. These results suggest that TRAIL is a promising agent for the clinical treatment of t(8;21) AML.

Omics Technologies to Decipher Regulatory Networks in Granulocytic Cell Differentiation.

Induced granulocytic differentiation of human leukemic cells under all-trans-retinoid acid (ATRA) treatment underlies differentiation therapy of acute myeloid leukemia. Knowing the regulation of this process it is possible to identify potential targets for antileukemic drugs and develop novel approaches to differentiation therapy. In this study, we have performed transcriptomic and proteomic profiling to reveal up- and down-regulated transcripts and proteins during time-course experiments. Using data on differentially expressed transcripts and proteins we have applied upstream regulator search and obtained transcriptome- and proteome-based regulatory networks of induced granulocytic differentiation that cover both up-regulated (HIC1, NFKBIA, and CASP9) and down-regulated (PARP1, VDR, and RXRA) elements. To verify the designed network we measured HIC1 and PARP1 protein abundance during granulocytic differentiation by selected reaction monitoring (SRM) using stable isotopically labeled peptide standards. We also revealed that transcription factor CEBPB and LYN kinase were involved in differentiation onset, and evaluated their protein levels by SRM technique. Obtained results indicate that the omics data reflect involvement of the DNA repair system and the MAPK kinase cascade as well as show the balance between the processes of the cell survival and apoptosis in a p53-independent manner. The differentially expressed transcripts and proteins, predicted transcriptional factors, and key molecules such as HIC1, CEBPB, LYN, and PARP1 may be considered as potential targets for differentiation therapy of acute myeloid leukemia.

Genome-wide miRNA profiling and pivotal roles of miRs 125a-5p and 17-92 cluster in human neutrophil maturation and differentiation of acute myeloid leukemia cells.

MicroRNAs (miRNAs, miRs) are short non-coding post-transcriptional regulators of gene expression in normal physiology and disease. Acute myeloid leukemia is characterized by accumulation of malignantly transformed immature myeloid precursors, and differentiation therapy, used to overcome this differentiation blockage, has become a successful therapeutic option. The human HL-60 acute leukemia cell line serves as a cell culture model for granulocytic maturation, and dimethyl sulfoxide (DMSO) incubation leads to its differentiation towards neutrophil-like cells, as assessed by biochemical, functional and morphological parameters. DMSO-induced HL-60 cell differentiation constitutes an excellent model to examine molecular processes that turn a proliferating immortal leukemic cell line into mature non-proliferating and apoptosis-prone neutrophil-like end cells. By performing genome-wide miRNA profiling and functional assays, we have identified a signature of 86 differentially expressed canonical miRNAs (51 upregulated; 35 downregulated) during DMSO-induced granulocytic differentiation of HL-60 cells. Quantitative real-time PCR was used to validate miRNA expression. Among these differentially expressed canonical miRNAs, we found miR-125a-5p upregulation and miR-17-92 cluster downregulation acted as major regulators of granulocytic differentiation in HL-60 cells. Enforced expression of miR-125a-5p promoted granulocytic differentiation in HL-60 cells, whereas miR-17-92 ectopic expression inhibited DMSO-induced HL-60 granulocytic differentiation. Ectopic expression of miR-125a-5p also promoted granulocytic differentiation in human acute promyelocytic leukemia NB4 cells, as well as in naïve human primary CD34+-hematopoietic progenitor/stem cells. These findings provide novel molecular insights into the identification of miRNAs regulating granulocytic differentiation of human leukemia cells and normal CD34+-hematopoietic progenitor/stem cells, and may assist in the development of novel miRNA-targeted therapies for leukemia.

Chromatin remodeling mediated by ARID1A is indispensable for normal hematopoiesis in mice

Precise regulation of chromatin architecture is vital to physiological processes including hematopoiesis. ARID1A is a core component of the mammalian SWI/SNF complex, which is one of the ATP-dependent chromatin remodeling complexes. To uncover the role of ARID1A in hematopoietic development, we utilized hematopoietic cell-specific deletion of Arid1a in mice. We demonstrate that ARID1A is essential for maintaining the frequency and function of hematopoietic stem cells and its loss impairs the differentiation of both myeloid and lymphoid lineages. ARID1A deficiency led to a global reduction in open chromatin and ensuing transcriptional changes affected key genes involved in hematopoietic development. We also observed that silencing of ARID1A affected ATRA-induced differentiation of NB4 cells, suggesting its role in granulocytic differentiation of human leukemic cells. Overall, our study provides a comprehensive elucidation of the function of ARID1A in hematopoiesis and highlights the central role of ARID1A-containing SWI/SNF complex in maintaining chromatin dynamics in hematopoietic cells.

JS-K induces reactive oxygen species-dependent anti-cancer effects by targeting mitochondria respiratory chain complexes in gastric cancer.

As a nitric oxide (NO) donor prodrug, JS‐K inhibits cancer cell proliferation, induces the differentiation of human leukaemia cells, and triggers apoptotic cell death in various cancer models. However, the anti‐cancer effect of JS‐K in gastric cancer has not been reported. In this study, we found that JS‐K inhibited the proliferation of gastric cancer cells in vitro and in vivo and triggered mitochondrial apoptosis. Moreover, JS‐K induced a significant accumulation of reactive oxygen species (ROS), and the clearance of ROS by antioxidant reagents reversed JS‐K‐induced toxicity in gastric cancer cells and subcutaneous xenografts. Although JS‐K triggered significant NO release, NO scavenging had no effect on JS‐K‐induced toxicity in vivo and in vitro. Therefore, ROS, but not NO, mediated the anti‐cancer effects of JS‐K in gastric cancer. We also explored the potential mechanism of JS‐K‐induced ROS accumulation and found that JS‐K significantly down‐regulated the core proteins of mitochondria respiratory chain (MRC) complex I and IV, resulting in the reduction of MRC complex I and IV activity and the subsequent ROS production. Moreover, JS‐K inhibited the expression of antioxidant enzymes, including copper‐zinc‐containing superoxide dismutase (SOD1) and catalase, which contributed to the decrease of antioxidant enzymes activity and the subsequent inhibition of ROS clearance. Therefore, JS‐K may target MRC complex I and IV and antioxidant enzymes to exert ROS‐dependent anti‐cancer function, leading to the potential usage of JS‐K in the prevention and treatment of gastric cancer.

Diallyl disulfide down-regulates calreticulin and promotes C/EBPα expression in differentiation of human leukaemia cells.

Diallyl disulfide (DADS), the main active component of the cancer fighting allyl sulfides found in garlic, has shown potential as a therapeutic agent in various cancers. Previous studies showed DADS induction of HL‐60 cell differentiation involves down‐regulation of calreticulin (CRT). Here, we investigated the mechanism of DADS‐induced differentiation of human leukaemia cells and the potential involvement of CRT and CCAAT enhancer binding protein‐α (C/EBPα). We explored the expression of CRT and C/EBPα in clinical samples (20 healthy people and 19 acute myeloid leukaemia patients) and found that CRT and C/EBPα expressions were inversely correlated. DADS induction of differentiation of HL‐60 cells resulted in down‐regulated CRT expression and elevated C/EBPα expression. In severe combined immunodeficiency mice injected with HL‐60 cells, DADS inhibited the growth of tumour tissue and decreased CRT levels and increased C/EBPα in vivo. We also found that DADS‐mediated down‐regulation of CRT and up‐regulation of C/EBPα involved enhancement of reactive oxidative species. RNA immunoprecipitation revealed that CRT bound C/EBPα mRNA, indicating its regulation of C/EBPα mRNA degradation by binding the UG‐rich element in the 3′ untranslated region of C/EBPα. In conclusion, the present study demonstrates the C/EBPα expression was correlated with CRT expression in vitro and in vivo and the molecular mechanism of DADS‐induced leukaemic cell differentiation.

NM23 downregulation and lysophosphatidic acid receptor EDG2/lpa1 upregulation during myeloid differentiation of human leukemia cells

The NM23 gene is overexpressed in many hematological malignancies and its overexpression predicts poor treatment outcomes. NM23 overexpression is thought to suppress myeloid differentiation of leukemia cells, but the molecular mechanism is unknown. In breast cancer cells, the lysophosphatidic acid (LPA) receptor EDG2/lpa1 was downregulated by NM23-H1 overexpression, and this reciprocal expression pattern was associated with suppressed or induced cell motility/metastasis. Here, we examined the relationship between EDG2 and NM23 expression during myeloid differentiation of leukemia cells. NM23 expression decreased and EDG2 expression increased during all-trans retinoic acid (ATRA)-induced myeloid differentiation of HL-60, NB4, and THP-1 leukemia cells. Moreover, this inverse correlation was more evident when myeloid differentiation was enhanced by ellagic acid, an inhibitor of NM23 activity. In contrast, there was no inverse correlation between EDG2 and NM23 expression during erythroid differentiation of HEL and K562 cells. ATRA plus LPA enhanced the motility of leukemia cells as well as breast cancer cells in an EDG2-dependent manner. These results suggest a common molecular mechanism between myeloid differentiation of leukemia cells and migration of breast cancer cells depending on NM23 and EDG2 expression levels.

Identification of potential targets for differentiation in human leukemia cells induced by diallyl disulfide.

Diallyl disulfide (DADS) is a primary component of garlic, which has chemopreventive potential. We previously found that moderate doses (15-120µM) of DADS induced apoptosis and G2/M phase cell cycle arrest. In this study, we observed the effect of low doses (8µM) of DADS on human leukemia HL-60 cells. We found that DADS could inhibit proliferation, migration and invasion in HL-60 cells, and arrested cells at G0/G1stage. Then, cell differentiation was displayed by morphologic observation, NBT reduction activity and CD11b evaluation of cytometric flow. It showed that DADS induced differentiation, reduced the ability of NBT and increased CD11b expression. Likewise, DADS inhibited xenograft tumor growth and induced differentiation invivo. In order to make sure how DADS induced differentiation, we compared the protein expression profile of DADS-treated cells with that of untreated control. Using high resolution mass spectrometry, we identified 18differentially expressed proteins after treatment with DADS, including four upregulated and 14downregulated proteins. RT-PCR and western blot assay showed that DJ-1, cofilin1, RhoGDP dissociation inhibitor2 (RhoGDI2), Calreticulin (CTR) and PCNA were decreased by DADS. These data suggest that the effects of DADS on leukemia may be due to multiple targets for intervention.

Anti-leukemic activity of DNA methyltransferase inhibitor procaine targeted on human leukaemia cells

AbstractChromatin remodeling in DNA is fundamental to gene expression, DNA replication and repair processes. Methylation of promoter regions of tumor-suppressor genes and histone deacetylation leads to gene silencing and transcriptionally repressive chromatin. For the past few decades DNA methylation agents became very attractive as the targets for cancer therapy. The purpose of this work was to examine the effects of DNMT inhibitor procaine on growth inhibition, apoptosis and differentiation of human leukaemia cells. The changes in expression of genes, proteins and histone modifications caused by procaine were evaluated under different treatments. We demonstrated that procaine arrests growth of human leukaemia cells and in combination with all-trans retinoic acid (ATRA) induces cancer cell differentiation. Procaine causes reduction of expression of DNA methyltransferases as well. The treatment of human leukaemia cells with procaine increase the expression of molecules associated with differentiation (CD11b, E-cadherin, G-CSF) and apoptosis (PPARγ). Moreover, the examined DNMT inhibitor enhances certain gene transcription activation via chromatin remodelling – the changes in histone H3K4(Me)3 and H3K9Ac/S10P modifications were detected. Our results suggest, that DNMT inhibitor – procaine, can be used for further investigations on epigenetic differentiation therapy of leukaemia cells especially when used in combination with retinoic acid.

LukS-PV induces differentiation by activating the ERK signaling pathway and c-JUN/c-FOS in human acute myeloid leukemia cells

LukS-PV, a component of Panton–Valentine leukocidin, is a pore-forming cytotoxin secreted by Staphylococcus aureus. Here we examined the potential effect of LukS-PV in differentiation of human leukemia cells and the underlying mechanism. We found that LukS-PV could induce differentiation of human acute myeloid leukemia (AML) cells, including AML cell lines and primary AML blasts, as determined by morphological changes, phagocytosis assay and expression of CD14 and CD11b surface antigens. In addition, LukS-PV activated the extracellular signal-regulated kinase (ERK) pathway and significantly upregulated the phosphorylation of c-JUN and c-FOS transcriptional factors in the process of differentiation. Inhibiting ERK pathway activation with U0126 (a MEK1/2 inhibitor) markedly blocked LukS-PV-induced differentiation and decreased the phosphorylation of c-JUN and c-FOS. These findings demonstrate an essential role for the ERK pathway together with c-JUN and c-FOS in the differentiation activity of LukS-PV. Taken together, our data suggest that LukS-PV could be a potential candidate as a differentiation-inducing agent for the therapeutic treatment of AML.

Myeloid-Related Protein S100A9 Induces Cellular Differentiation in Acute Myeloid Leukemia through TLR2 and TLR4 Receptors

The myeloid-related proteins S100A8 (MRP8) and S100A9 (MRP14) are endogenous alarmins abundantly and constitutively expressed by myeloid cells (neutrophils, monocytes and immature myeloid cells). S100A8 and S100A9 proteins exist as homodimers but also associate to form the heterodimer calprotectin (S100A8/A9) and are up-regulated in several inflammatory diseases and human cancers. In patients with acute myeloid leukemia (AML), the concentration of S100A8/A9 in serum is elevated and the expression of S100A8 correlates with poor prognosis. However, the role of these proteins in hematologic malignancies is largely unknown.Here, we studied the roles of S100A8 and S100A9 in a mouse model ofAML induced by overexpression of Hoxa9 and Meis1 (H9M1). As observed in human, mice developing AML have a substantial increase in S100A8/A9 their serum (5.0µg/ml ± 1.0µg/mL vs 0.5µg/mL ± 0.1µg/mL for the control, p<0.0001). Using S100A8KO and S100A9KO mice, we demonstrated that S100A8/A9 proteins found in the sera are secreted by leukemic cells and not by the micro-environment.To investigate if secreted S100A8 and S100A9 proteins play a role in leukemogenesis, H9M1 AML were transplanted to secondary recipients were treated intraperitoneally (i.p) with anti-S100A8 or anti-S100A9 antibodies. Blocking S100A8 led to a marked delay in leukemia progression and significantly extended survival compared to control immunoglobulins (IgG) (31 days vs 39.5 days, p=0.010) with an increase of the CD11b+ Gr-1+ double positive population (78.8%±1.4 vs 90.1%±3, p=0.038). In contrast, no differences in overall survival were observed between control IgG and anti-S100A9 treated mice. In addition, we demonstrate that anti-S100A8 treatments reduced AML cell proliferation through the G0/G1 cell cycle arrest. Thus, blocking S100A8 reduces leukemogenesis and induced leukemic blast maturation in AML.To further investigate the roles of S100A8 and S100A9 in AML, we treated secondary H9M1 mice with S100A8 or S100A9 proteins i.p three times per week. Interestingly, injection of S100A8 had no effect on AML latency, but S100A9 treatment resulted in significant delays of leukemia symptoms suggesting an anti-leukemic activity (32 days vs 41 days, p=0.0045). The extent of increased survival induced by S100A9 treatment was similar to standard induction chemotherapy using combination of doxorubicin and cytarabine. Furthermore, S100A9 treatment led to significant cell cycle arrest and an increase of mature cells marker CD11band Gr-1 in bone marrow (76.6%± 1.0% vs 94.8 ± 1.2%, p<0.0001). Analysis of leukemic cells morphology confirmed that S100A9 modulates AML cells maturation.Since injection of the S100A9 protein and anti-S100A8 antibody had similar effect on AML progression and cellular differentiation, we postulated that cell differentiation is regulated by the balance between S100A9 and S100A8. To test the hypothesis, cells were cultured in vitro in presence of different ratio of S100A9 on S100A8. At high ratio (S100A9>S100A8), the percentage of CD11b+ Gr-1+ was increased compared to the control suggesting that leukemic cells underwent differentiation. Nevertheless, the augmentation of S100A8 level prevented the increases of CD11b+ Gr-1+ mediated by S100A9.To test the ability of S100A9 protein to promote terminal cell differentiation of human leukemia, human cord blood (CB) CD34+ cells were transduced with retrovirus expressing the oncogene MLL-AF9. In vitro, S100A9 induced a 10-fold up-regulation of CD14 expression in MLL-AF9 cells. More importantly, the increase of CD14 was associated with morphological changes typical of terminal differentiation into monocytes and then macrophages. To determine the receptor(s) involved in regulation of cellular differentiation induced by S100A9 in human AML, we followed CD14 expression in presence of anti-TLR neutralizing antibodies. Blockage of TLR4 and TLR2 prevented the differentiation of human leukemic cells mediated by S100A9.Taken together, we show that increasing the S100A9/S100A8 ratio in murine AML, either by anti-S100A8 antibody or recombinant S100A9 protein, prolong the survival of secondary mice in vivo by inducing differentiation on AML cells. We corroborated these data in human MLL-AF9 cells in vitro and show that S100A9 protein induces terminal differentiation through TLR receptors which could represent a new therapeutic target to explore. DisclosuresNo relevant conflicts of interest to declare.

Induction of human leukemia cell differentiation via PKC/MAPK pathways by arsantin, a sesquiterpene lactone from Artemisia santolina.

Sesquiterpene lactone compounds have received considerable attention in pharmacological research due to their therapeutic effects including anti-cancer and anti-inflammatory activities. In this report, we investigated the effect of arsantin, a sesquiterpene lactone compound present in Artemisia santolina, on cellular differentiation in the human promyelocytic leukemia HL-60 cell culture system. Arsantin significantly induced HL-60 cell differentiation in a concentration-dependent manner. Cytofluorometric analysis indicated that arsantin induced HL-60 cell differentiation predominantly into granulocytes. Both PKC and MAPK inhibitors suppressed the HL-60 cell differentiation induced by arsantin. Moreover, treatment with arsantin increased protein levels of PKCα and PKCβII isoforms, and also induced increased protein levels and phosphorylation form of MAPKs in HL-60 cells. Importantly, arsantin synergistically enhanced differentiation of HL-60 cells in a dose-dependent manner when combined with either low doses of 1,25-(OH)2D3 or ATRA. The ability to enhance the differentiation potential of 1,25-(OH)2D3 or ATRA by arsantin may improve outcomes in the therapy of acute promyelocytic leukemia.

Arachidonic acid enhances TPA-induced differentiation in human leukemia HL-60 cells via reactive oxygen species-dependent ERK activation

The phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), is a potent stimulator of differentiation in human leukemia cells; however, the effects of arachidonic acid (AA) on TPA-induced differentiation are still unclear. In the present study, we investigated the contribution of AA to TPA-induced differentiation of human leukemia HL-60 cells. We found that treatment of HL-60 cells with TPA resulted in increases in cell attachment and nitroblue tetrazolium (NBT)-positive cells, which were significantly enhanced by the addition of AA. Stimulation of TPA-induced intracellular reactive oxygen species (ROS) production by AA was detected in HL-60 cells via a DCHF-DA analysis, and the addition of the antioxidant, N-acetyl-cysteine (NAC), was able to reduce TPA+AA-induced differentiation in accordance with suppression of intracellular peroxide elevation by TPA+AA. Furthermore, activation of extracellular-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) by TPA+AA was identified in HL-60 cells, and the ERK inhibitor, PD98059, but not the JNK inhibitor, SP600125, inhibited TPA+AA-induced NBT-positive cells. Suppression of TPA+AA-induced ERK protein phosphorylation by PD98059 and NAC was detected, and AA enhanced ERK protein phosphorylation by TPA was in HL-60 cells. AA clearly increased TPA-induced HL-60 cell differentiation, as evidenced by a marked increase in CD11b expression, which was inhibited by NAC and PD98059 addition. Eicosapentaenoic acid (EPA) as well as AA showed increased intracellular peroxide production and differentiation of HL-60 cells elicited by TPA. Evidence of AA potentiation of differentiation by TPA in human leukemia cells HL-60 via activation of ROS-dependent ERK protein phosphorylation was first demonstrated herein.

Induction of differentiation-specific miRNAs in TPA-induced myeloid leukemia cells through MEK/ERK activation

Cellular microRNAs (miRNAs) are pivotal regulators involved in various biological processes through the post-transcriptional regulation of gene expression. Signaling pathways are extensively activated during 12-O-Tetradecanoylphorbol-13-acetate (TPA)-induced differentiation of human leukemia cells, but the modulation of miRNA expression and processing in this context has yet to be fully explored. In this study, we comprehensively analyzed 10miRNAs that are consistently upregulated during TPA-induced differentiation of various leukemia cell lines by employing microarray technology. The upregulation of these miRNAs was further verified by quantitative RT-PCR, and, markedly, a subset of the miRNAs was found to be induced via the MEK/ERK signaling pathway using TPA and specific pharmacological inhibitors. Moreover, immunoblotting and quantitative RT-PCR analysis demonstrated that the expression levels of key miRNA processing machineries (i.e., Drosha, Dicer, Ago1 and Ago2) were not induced in this context, but the transcription of the miRNA products was triggered by MEK/ERK activation. Therefore, we identified the unique miRNAs that respond to TPA treatment in leukemia cells and demonstrated the essential role of the MEK/ERK signaling pathway in the induction of these miRNA transcripts.

Ginsenoside Rh2 induces cell cycle arrest and differentiation in human leukemia cells by upregulating TGF-β expression

The triterpene saponin ginsenoside Rh2 has been shown to have antiproliferative effects on various cancer cells. However, the effect of Rh2 on the cell cycle and its underlying molecular mechanism in human leukemia cells are not fully understood. In this study, we found that Rh2 inhibited the proliferation of human leukemia cells concentration- and time-dependently with an IC(50) of ~38 µM. DNA flow cytometric analysis indicated that Rh2 blocked cell cycle progression at the G(1) phase in HL-60 and U937 cells, and this was found to be accompanied by the downregulations of cyclin-dependent kinase (CDK) 4, CDK6, cyclin D1, cyclin D2, cyclin D3 and cyclin E at the protein level. However, CDK inhibitors (CDKIs), such as p21(CIP1/WAF1) and p27(KIP1), were gradually upregulated after Rh2 treatment at the protein and messenger RNA (mRNA) levels. In addition, Rh2 markedly enhanced the bindings of p21(CIP1/WAF1) and p27(KIP1) to CDK2, CDK4 and CDK6, and these bindings reduced CDK2, CDK4 and CDK6 activities. Furthermore, Rh2 induced the differentiation of HL-60 cells as demonstrated by biochemical assays and the expression levels of cell surface antigens. In addition, treatment of HL-60 cells with Rh2 significantly increased transforming growth factor-β (TGF-β) production, and cotreatment with TGF-β neutralizing antibody prevented the Rh2-induced downregulations of CDK4 and CDK6, upregulations of p21(CIP1/WAF1) and p27(KIP1) levels and the induction of differentiation. These results demonstrate that the Rh2-mediated G(1) arrest and the differentiation are closely linked to the regulation of TGF-β production in human leukemia cells.

Ganoderma lucidum Polysaccharides Induce Macrophage‐Like Differentiation in Human Leukemia THP‐1 Cells via Caspase and p53 Activation

Differentiation therapy by induction of tumor cells is an important method in the treatment of hematological cancers such as leukemia. Tumor cell differentiation ends cancer cells' immortality, thus stopping cell growth and proliferation. In our previous study, we found that fucose-containing polysaccharide fraction F3 extracted from Ganoderma lucidum can bring about cytokine secretion and cell death in human leukemia THP-1 cells. This prompted us to further investigate on how F3 induces the differentiation in human leukemia cells. We integrated time-course microarray analysis and network modeling to study the F3-induced effects on THP-1 cells. In addition, we determined the differentiation effect using Liu's staining, nitroblue tetrazolium (NBT) reduction assay, flow cytometer, western blotting and Q-PCR. We also examined the modulation and regulation by F3 during the differentiation process. Dynamic gene expression profiles showed that cell differentiation was induced in F3-treated THP-1 cells. Furthermore, F3-treated THP-1 cells exhibited enhanced macrophage differentiation, as demonstrated by changes in cell adherence, cell cycle arrest, NBT reduction and expression of differentiation markers including CD11b, CD14, CD68, matrix metalloproteinase-9 and myeloperoxidase. In addition, caspase cleavage and p53 activation were found to be significantly enhanced in F3-treated THP-1 cells. We unraveled the role of caspases and p53 in F3-induced THP-1 cells differentiation into macrophages. Our results provide a molecular explanation for the differentiation effect of F3 on human leukemia THP-1 cells and offer a prospect for a potential leukemia differentiation therapy.

Small Rab GTPase Rab7b promotes megakaryocytic differentiation by enhancing IL-6 production and STAT3-GATA-1 association

Induction of the differentiation of human leukemia cells is a useful strategy in treatment of human leukemia. However, the molecular mechanisms involved in leukemia cell differentiation have not been fully elucidated. Interleukin 6 (IL-6) is a pleiotropic cytokine acting on a variety of cell types, and plays important roles in hematopoiesis. GATA binding protein 1 (GATA-1) is an important transcription factor involved in either megakaryocytic or erythrocytic differentiation. Herein we report that Rab7b, a late endosome/lysosome-localized myeloid small GTPase, promotes phorbol-12-myristate-13-acetate (PMA)-induced megakaryocytic differentiation by increasing nuclear factor κB (NF-κB)-dependent IL-6 production and subsequently enhancing the association of activated signal transducer and activator of transcription 3 (STAT3) with GATA-1. By using PMA-induced megakaryocytic differentiation of leukemia cells as a model, we investigated the roles of Rab7b in megakaryocytic differentiation. We find that Rab7b can potentiate PMA-induced upregulation of megakaryocytic markers, production of IL-6, and activation of NF-κB. Inhibitor of NF-κB and neutralizing antibodies for IL-6 or the IL-6 signaling receptor gp130 can block the effects of Rab7b in megakaryocytic differentiation. In Rab7b-silenced cells, PMA-induced activation of NF-κB, IL-6 production, and megakaryocytic differentiation are impaired. Furthermore, we demonstrate that IL-6-induced activation of STAT3 and the subsequent association of STAT3 with GATA-1 may contribute to PMA-induced and Rab7b-mediated transcriptional upregulation of megakaryocytic differentiation markers. Therefore, our data suggest that Rab7b may play important roles in megakaryopoiesis by activating NF-κB and promoting IL-6 production. Our study also indicates that the IL-6-induced association of STAT3 with GATA-1 may regulate megakaryocytic differentiation.

Diterpenes from Xylopia langsdorffiana Inhibit Cell Growth and Induce Differentiation in Human Leukemia Cells

Two new diterpenes were isolated from stems and leaves of Xylopia langsdorffiana, ent-atisane-7alpha,16alpha-diol (xylodiol) and ent-7alpha-acetoxytrachyloban-18-oic acid (trachylobane), along with the known 8(17),12E,14-labdatrien-18-oic acid (labdane). We investigated their antitumour effects on HL60, U937 and K562 human leukemia cell lines. We found that xylodiol was the most potent diterpene in inhibiting cell proliferation of HL60, U937 and K562 cells, with mean IC50 values of 90, 80 and 50 microM, respectively. Based on the nitroblue tetrazolium (NBT) reduction assay, all the diterpenes were found to induce terminal differentiation in HL60 and K562 cells, with xylodiol being the most effective. NBT reduction was increased by almost 120% after 12 h exposure of HL60 cells to xylodiol at a concentration lower than the IC50 (50 microM). Thus, xylodiol inhibited human leukemia cell growth in vitro partly by inducing cell differentiation, and merits further studies to examine its mechanism of action as a potential antitumoural agent.