利用K562红细胞分化模型和cDNA芯片技术筛选参与红细胞分化的新基因(英文)

以氯高铁血红素 (hemin)诱导K5 6 2分化作为体外红细胞分化模型 ,结合cDNA大规模测序、生物信息学分析、基因芯片杂交和NorthernBlot分析等技术 ,筛选红细胞分化相关的新基因 .首先利用大规模测序技术从人胚肾cDNA文库中随机挑选克隆测得 192个EST(expressedsequencetags)片段 ,经在线生物信息学分析 ,得到 79个代表新基因的未知EST片段 ,并在NCBI(NationalCenterofBiotechnologyInformation)dbEST库中登录 .利用 79个ESTcDNA片段制备了基因芯片 .提取分化前后的K5 6 2细胞的mRNA作为荧光标记反转录的模板 ,反转录后的探针用于DNA芯片杂交 .分析杂交后的结果 ,得到了 2个差异表达较明显的基因 ,GenBank登录号分别为AF147772 (187bp)和AF4 776 2(6 30bp) ,并分别命名为EDRG1和EDRG2 (erythroiddifferentiationrelatedgene 1and 2 ) ,相似性检索表明它们属全新基因 ,基因组草图测序数据库检索表明了两个基因的染色体定位 .随后的Northern印迹用于验证了在分化前后的K5 6 2细胞中差异表达 .提示这两个基因参与了红细胞分化过程 .RT PCR检测了EDRG1和EDRG2在人胚胎多组织中的表达 .结果提示 ,EDRG1可能与多种胚组织的正常发育相关 ,尤其在胚脑中高丰度表达 ,而EDRG2则可能参与了胚心和胚肾的组织生成 .生物     

Role of G proteins and ERK activation in hemin-induced erythroid differentiation of K562 cells

Heterotrimeric G proteins which couple extracellular signals to intracellular effectors play a central role in cell growth and differentiation. The pluripotent erythroleukemic cell line K562 that acquires the capability to synthesize hemoglobin in response to a variety of agents can be used as a model system for erythroid differentiation. Using Western blot analysis and RT-PCR, we studied alterations in G protein expression accompanying hemin-induced differentiation of K562 cells. We demonstrated the presence of G(alpha s), G(alpha i2) and G(alpha q) and the absence of G(alpha i1), G(alpha o) and G(alpha 16) in K562 cells. We observed the short form of G(alpha s) to be expressed predominantly in these cells. Treatment of K562 cells with hemin resulted in an increase in the levels of G(alpha s) and G(alpha q). On the other hand, the level of G(alpha i2) was found to increase on the third day after induction with hemin, followed by a decrease to levels lower of those of uninduced cells. The mitogen-activated protein kinase ERK1/2 pathway is crucial in the control of cell proliferation and differentiation. Both Gi- and Gq-coupled receptors stimulate MAPK activation. We therefore examined the phosphorylation of ERK1/2 during hemin-induced differentiation of K562 cells. Using anti-ERK1/2 antibodies, we observed that ERK2 was primarily phosphorylated in K562 cells. ERK2 phosphorylation increased gradually until 48 h and returned to basal values by 96 h following hemin treatment. Our results suggest that changes in G protein expression and ERK2 activity are involved in hemin-induced differentiation of K562 cells.     

Role of ERK activation in growth and erythroid differentiation of K562 cells

Inhibition of signaling through Ras in BCR-ABL-positive pluripotent K562 cells leads to apoptosis and spontaneous differentiation. However, Ras-induced activation of the mitogen-activated protein kinase ERK has been suggested to play a critical role in either growth or differentiation in different model systems. We studied the role of ERK activation in the growth-promoting and anti-apoptotic effect of Ras and its involvement in hemin-induced nonterminal erythroid differentiation using the BCR-ABL-positive K562 cell line as a model. K562 cells were stably transfected with ERK1 or the dominant inhibitory mutant of ERK1 (ERK1-KR). Overexpression of ERK1-KR inhibited cell growth with an approximately fourfold increase in doubling time and induced apoptosis in K562 cells. Incubation with the MEK1 inhibitor UO126 inhibited cell growth and induced apoptosis in K562 cells in a dose-dependent manner as well. In the presence of exogenously added hemin, K562 cells differentiate into erythroblasts, as indicated by the production of large amounts of fetal hemoglobin. We examined the activation of MAP kinases during hemin-induced differentiation. The ERK1 and 2 activity increased within 2 h post hemin treatment and remained elevated for 24-48 h. During this time, fetal hemoglobin synthesis also increases from 0.8 to 10 pg/cell. There was no activation of JNK or p38 protein kinases. The hemin-induced accumulation of hemoglobin was inhibited in ERK1-KR overexpressing cells and was enhanced in the wild-type ERK1 transfectants. Our results suggest that ERK activation is involved in both growth and hemin-induced erythroid differentiation in the BCR-ABL-positive K562 cell line.     

ERK2-Pyruvate Kinase Axis Permits Phorbol 12-Myristate 13-Acetate-induced Megakaryocyte Differentiation in K562 Cells

Metabolic changes that contribute to differentiation are not well understood. Overwhelming evidence shows the critical role of glycolytic enzyme pyruvate kinase (PK) in directing metabolism of proliferating cells. However, its role in metabolism of differentiating cells is unclear. Here we studied the role of PK in phorbol 12-myristate 13-acetate (PMA)-induced megakaryocytic differentiation in human leukemia K562 cells. We observed that PMA treatment decreased cancer-type anabolic metabolism but increased ATP production, along with up-regulated expression of two PK isoforms (PKM2 and PKR) in an ERK2-dependent manner. Interestingly, silencing of PK (PKM2 and PKR) inhibited PMA-induced megakaryocytic differentiation, as revealed by decreased expression of megakaryocytic differentiation marker CD61 and cell cycle behavior. Further, PMA-induced ATP production reduced greatly upon PK silencing, suggesting that PK is required for ATP synthesis. In addition to metabolic effects, PMA treatment also translocated PKM2, but not PKR, into nucleus. ERK1/2 knockdowns independently and together suggested the role of ERK2 in the up-regulation of both the isoforms of PK, proposing a role of ERK2-PK isoform axis in differentiation. Collectively, our findings unravel ERK2 guided PK-dependent metabolic changes during PMA induction, which are important in megakaryocytic differentiation.     

Fluctuation of gene expression for poly(ADP-ribose) synthetase during hemin-induced erythroid differentiation of human leukemia K562 cells and its reversion process

We have studied the regulation of gene expression for poly(ADP-ribose) synthetase during erythroid differentiation and its reversion process. When human leukemia K562 cells were incubated in the presence of 80 microM hemin, benzidine-positive cells appeared at day 2 and 90% of the cells became positive at day 6. However, RNA blot analysis reveals that mRNA for gamma-globin was already abundant in untreated K562 cells and the level of the message was slightly increased by hemin-treatment. Spectroscopic analysis and polyacrylamide gel electrophoresis of the induced cell extracts indicate that hemoglobin molecules were not detected in untreated cells, and increased successively up to day 6. The hemin-induced cells were thoroughly washed, and then recultured in the absence of hemin. The benzidine-positive cells mostly disappeared 3 days after the elimination of the inducer. During the hemin-induced erythroid differentiation, the activity and mRNA for poly(ADP-ribose) synthetase decreased to 50% and 20% of the initial level at day 3 and a low level of the gene expression was maintained afterwards, whereas the activity and mRNA returned to the initial value 1 day after hemin elimination. The results indicate that the hemin-induced erythroid differentiation of K562 cells is a reversible process and depression of the synthetase may be involved in the progress of differentiation.     

Extracellular signal-regulated kinase/90-KDA ribosomal S6 kinase/nuclear factor-kappa B pathway mediates phorbol 12-myristate 13-acetate-induced megakaryocytic differentiation of K562 cells

Two signaling pathways, the extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK)-dependent pathway and the nuclear factor-kappaB (NF-kappaB)-dependent pathway, have been known to mediate megakaryocytic differentiation of K562 cells induced by phorbol 12-myristate 13-acetate (PMA). In this study, we examined whether 90-kDa ribosomal S6 kinase (RSK), known as a substrate of ERK/MAPK and a signal-inducible IkappaBalpha kinase, would link two pathways during the differentiation. RSK1 was activated in a time- and dose-dependent manner during the PMA-induced differentiation. Overexpression of wild-type or dominant inhibitory mutant (D205N) of RSK1 enhanced or suppressed PMA-stimulated NF-kappaB activation and megakaryocytic differentiation as shown by morphology, nonspecific esterase activity, and expression of the CD41 megakaryocytic marker, respectively. In addition, overexpression of the dominant inhibitory mutant (S32A/S36A) of IkappaBalpha inhibited PMA-stimulated and RSK1-enhanced megakaryocytic differentiation, indicating that NF-kappaB mediates a signal for megakaryocytic differentiation downstream of RSK1. PMA-stimulated activation of ERK/MAPK, RSK1, and NF-kappaB and the PMA-induced megakaryocytic differentiation were prevented by pretreatment with PD98059, a specific inhibitor of the mitogen-activated ERK kinase (MEK). Therefore, these results demonstrate that the sequential ERK/RSK1/NF-kappaB pathway mediates PMA-stimulated megakaryocytic differentiation of K562 cells.     

Nitric oxide levels during erythroid differentiation in K562 cell line

Nitric oxide (NO) is endogenous mediator of numerous physiological processes that range from regulation cardiovascular function and neurotransmission to antipathogenic and tumoricidal responses. This study was designed to investigate the possible role of NO during erythroid differentiation in K562 erythroleukemia cells. The chronic myelogenous leukemia (K562) cell line can be triggered in culture to differentiate along the erythrocytic pathway, in response to a variety of stimulatory agents. In this study, K562 cells were induced to synthesize hemoglobin by hemin. We investigated NOx (nitrate+nitrite) levels in uninduced (control) and hemin-induced K562 cell lysates during erythroid differentiation. Our results showed that NO levels decreased significantly on fourth and sixth day both in hemin-induced and control cells; the decrease was, however, more in hemin-induced group than in control group.     

A Role for the MEK/MAPK Pathway in PMA-Induced Cell Cycle Arrest: Modulation of Megakaryocytic Differentiation of K562 Cells

In vitromegakaryocytic differentiation of the pluripotent K562 human leukemia cell line is induced by PMA. Treatment of K562 cells with PMA results in growth arrest, polyploidy, morphological changes, and increased cell–cell and cell–substrate adhesion. These PMA-induced changes in K562 cells are preceded by a rapid rise in the activity of MEK (MAP kinase/extracellular regulated kinases) that leads to a sustained activation of ERK2 (extracellular regulated kinase; MAPK). Blockade of MEK1 activation by PD098059, a recently described specific MEK inhibitor [D. T. Dudleyet al.(1995).Proc. Natl. Acad. Sci. USA92, 7686–7689], reverses both the growth arrest and the morphological changes of K562 cells induced by PMA treatment. These changes are not associated with a disruption of PMA-induced down-regulation of BCR-ABL kinase or early integrin signaling events but are associated with a block of the cell-surface expression of the gpIIb/IIIa (CD41) integrin, a cell marker of megakaryocytic differentiation. These results demonstrate that the PMA-induced signaling cascade initiated by protein kinase C activation requires the activity of the MEK/ERK signaling complex to regulate cell cycle arrest, thus regulating the program that leads to the cell-surface expression of markers associated with megakaryocytic differentiation.     

cDNA cloning and function analysis of two novel erythroid differentiation related genes

Our previous studies showed that some nuclear proteins that wereexpressed especially during terminal differentiation of erythroid cells might interact directly or indirectly with HS2 sequence to form the HS2-protein complexes and thus play an important role in the globin gene regulation and erythroid differentiation. Monoclonal antibodies against the nuclear proteins of terminal differentiated erythroid cells, including intermediate and late erythroblasts of human fetal liver and hemin induced K562 cells, were prepared by hybridoma technique. The monoclonal antibodies were used to screen l-gtll human cDNA expression library of fetal liver in order to obtain the rele-vant cDNA clones. By the analysis of their cDNA clones and the identification of the proteins' func-tions, the regulation mechanism of the HS2 binding proteins might be better understood. Two cDNA clones (GenBank accession number AF040247 and AF040248 respectively) were obtained and one of them owns a full length and the other encodes a protein characterized by a leucine-zipper domain. Both of them were expressed differentially in K562 cells and hemin-induced K562 cells. The evidence suggested that both of them were involved in erythroid differentiation. We investigat-ed the expression pattern of EDRF1 and EDRF2 by RT-PCR technique. The results of RT-PCR suggested that EDRF1 and EDRF2 might play a critical role in early stage of organ development and histological differentiation. EDRF1 and EDRF2 might start the program of erythroid develop-ment, and also regulate the development of erythroid tissue and the expression of globin gene at different stage of the development.