Molecular mechanism involved in TPA-induced myelopoietic programming

Pardaxin Promoted Differentiation and Maturation of Leukemic Cells via Regulating TLR2/MyD88 Signal against Cell Proliferation

Objective

Leukemia is a cancer of the blood cells. Leukemic THP-1 and U937 cells were used in this study as monocytic effectors cells for proliferation responses and macrophage-like cells induction in leukemia. Pardaxin is an antimicrobial peptide isolated from the marine fish species.

Methods

After treatment for 5 days, pardaxin significantly suppressed cell viability and arrested cell cycle at G0/G1 phase in leukemic cells which were evaluated.

Results

Pardaxin also induced cell differentiation and maturation of THP-1 and U937 cells into macrophage-like cells with phagocytotic ability. Moreover, pardaxin elevated the expression of MyD88 but not toll-like receptor (TLR)-2 in both leukemic cells. TLR-2 blocking peptide was used to confirm that pardaxin attenuated phagocytotic ability and superoxide anion production in leukemic cells via activating MyD88 protein.

Conclusions

These findings suggested that pardaxin has a therapeutic potential for 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.

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.

Cholesterol-sensor initiates M. tuberculosis entry into human macrophages

Cholesterol-mediated mycobacteria entry into and survival within macrophages has added a new dimension to Tuberculosis research. The molecular mechanism through which cholesterol initiates this process is still poorly understood. The present study addressed to resolve this mechanism revealed that Mycobacterium tuberculosis possesses cholesterol-specific Receptor 'Ck'-like molecule responsible for mycobacterial entry into macrophages. Further human Receptor-Ck was found to regulate transcriptional expression of a gene that codes for Tryptophan-Aspartate containing coat (TACO) protein responsible for survival of mycobacteria within cells. Based upon these results, we propose that interaction of Receptor-Ck with cholesterol-rich membrane domains helps to create a 'Synaptic-junction' between mycobacteria and macrophage resulting in signalling events that are responsible for mycobacterium entry into and survival within macrophages.

Regulation of PPAR-gamma gene in human promyelocytic HL-60 cell line

The present study employed human promyelocytic cell line, HL-60, as an archetype model to understand the role of cholesterol receptors (Receptor-C(k) and oxysterol-specific receptor-transcription factor LxR-alpha) in the regulation of PPAR-gamma gene recognized to control cellular differentiation and apoptosis. Such a study revealed that Receptor "C(k)"-dependent signalling pathway not only regulates PPAR-gamma gene transcription but also provides ligands for the activation of this nuclear receptor superfamily of transcription factors that control hematopoiesis. Based upon these and our earlier results, we propose a molecular cross-talk pathway between cholesterol-specific cell surface Receptor-C(k) and nuclear receptors (LxR-alpha and PPAR-gamma), which may add a new dimension in the understanding and control of leukemogenesis.

Functional interaction of transcriptional coactivator ASC-2 and C/EBPalpha in granulocyte differentiation of HL-60 promyelocytic cell

HL-60 promyelocytic cells were treated with retinoic acid (RA) to stimulate granulocyte differentiation. CCAAT/enhancer binding protein alpha (C/EBPalpha) is known to be the molecular switch during early hematopoietic developmental events that direct cells to the granulocytic pathway. Here we show that the coactivator activating signal cointegrator-2 (ASC-2) plays an important role in differentiation of HL-60 cells into granulocytes by mediating C/EBPalpha-induced gene transcription. The differentiation inducer RA increased mRNA and protein expression of ASC-2. The protein-protein interaction of C/EBPalpha and ASC-2 was detected by coimmunoprecipitation during granulocyte differentiation. Subsequently, GST-pull-down assay revealed that the N-terminal transactivation domain of C/EBPalpha could interact with ASC-2. This functional interaction of ASC-2 with C/EBPalpha drove a synergistic enhancement of C/EBPalpha-dependent transactivation and overexpression of the N-terminal C/EBPalpha protein in HL-60 cells inhibited ASC-2 responsiveness for C/EBPalpha activity in granulocyte differentiation, indicating C/EBPalpha dependency of ASC-2 activity. Taken together, these results suggest that the differentiation-dependent expressed ASC-2 protein physically and functionally interacts with C/EBPalpha and increases its transactivation activity, regulating specific gene transcription for granulocyte differentiation.

Expression of receptor-Ck and SREBP genes in mononuclear cells from acute leukemia patients

We have recently shown that Receptor-Ck regulated genes, involved in cellular growth and death through a transcriptional factor (SREBP) which has affinity for sterol regulatory element (SRE) present in the promoter region of these genes. The present study revealed that blasts, derived from both ALL and AML patients, were unable to express SREBP gene product although they had the capacity to express Receptor-Ck gene product. These results which depict defective Receptor-Ck-dependent signalling are in conformity with our previous results which showed that lymphocytes from CML patients as well as other human leukemic cell lines are unable to express gene coding for Receptor-Ck leading again to a state of impaired Receptor-Ck-dependent signalling. On the basis of these results, we propose that deregulated Receptor-Ck-dependent signalling may have an important role in leukemogenesis.

Receptor-Ck regulates the expression of cyclin-dependent kinase inhibitors (p16; p27)

The present study was addressed to understand the interrelationship between Receptor-Ck induction-activation coupling; isoprenoids (derived from mevalonate pathway) and cyclin-dependent kinase inhibitors. The results reported here unambiguously reveal that isoprenoids regulate the expression of genes coding for CDK inhibited p16 and p27. Further, Receptor-Ck dependent signalling, known to control the mevalonate pathway, had a direct effect upon the p27 gene expression. Based upon these studies coupled with our earlier findings we propose that Receptor-Ck has an important role in the regulation of cell cycle machinery.