Involvement of Sp1/Sp3 in the activation of the GATA-1 erythroid promoter in K562 cells.

GATA-1 is a hematopoietic transcription factor that is essential for the terminal maturation of proerythroblasts, megakaryocytic cells and mast cells. The erythroid-specific promoter of the human GATA-1 gene directs the high expression of a reporter gene in K562 cells. Multiple putative transcription factor binding sites were identified in the promoter from the -860 to the -1 base pair (bp). For a better understanding of the transcriptional control of human GATA-1 gene expression, we tested the transcriptional activity of a series of deletions from the 5' end of the 860-bp promoter. A region between -221 and -128 bp retains most of the transcriptional activity of the full-length promoter. Deletion of the CGCCC box at -195 bp reduced reporter gene activity to 60.4%. Further deletion of the CACCC box at -173 bp nearly abolished reporter gene expression, indicating that the CACCC box is more critical. In vitro experiments of electrophoretic mobility shifts and in vivo studies using chromatin immuno-precipitation (ChIP) assays show that the Sp1/Sp3 proteins bind the CACCC site in the nuclei of K562 cells. Coincidently, hyperacetylation of histones in the GATA-1 erythroid promoter was also shown by ChIP assay. Co-transfection of Sp1 expression plasmids and plasmids with a wild-type promoter showed enhanced reporter gene activity in a dose-dependent manner. The combined data demonstrate that Sp1/Sp3, but not EKLF, is involved in the activation of the GATA-1 erythroid promoter, and that histones H3 and H4 are highly acetylated in this promoter region for an actively transcribed GATA-1 gene in K562 cells in which EKLF is barely detectable.

Functional analysis of multiple transcription factor sites in a regulatory element of human epsilon-globin gene.

The developmental control of the human epsilon-globin gene expression is mediated by transcriptional regulatory elements in the 5' flanking DNA of this gene. A previously identified negative regulatory element (-3028 to -2902 bp, termed epsilon-NRAII) was analyzed and one putative NF-kappaB site and two GATA sites locate at -3004 bp, -2975 bp and -2948 bp were characterized. Electrophoresis mobility shift assay (EMSA) showed that the putative NF-kappaB site was specifically bound by nuclear proteins of K562 cells. Data obtained from transient transfection showed that the expression of reporter gene could be upregulated about 50% or 100% respectively when epsilon-NRAII was inserted upstream of the SV40 promoter or epsilon-globin gene proximal promoter (-177 bp to +1 bp), suggesting that epsilon-NRAII might not be a classic silencer. Mutation in the putative NF-kappaB site or in the GATA site (at -2975 bp) slightly reduced the expression of reporter gene driven by SV40 promoter or epsilon-globin gene proximal promoter. However, the mutation of GATA site at -2948 bp remarkably reduced the reporter gene activity driven by SV40 promoter, but not by epsilon-globin gene proximal promoter. Further mutation analysis showed that the negative effect of mutation in GATA site at -2948 bp on SV40 promoter was not affected by the mutation of the putative NF-kappaB site, whereas it could be abolished by the mutation of GATA site at -2975 bp. Furthermore, the mutation of both GATA sites could synergistically reduce the reporter gene activity driven by epsilon-globin gene proximal promoter. Those results suggested that epsilon-NRAII might function differently on the SV40 promoter and epsilon-globin gene proximal promoter.

Effects of Huangqi (Hex) on inducing cell differentiation and cell death in K562 and HEL cells.

Huangqi (Astragalus membranaceus), a traditional Chinese medicine, has been used to ameliorate side effects of cancer chemotherapy in China. However, little is known about its molecular mechanisms. Here we show that induction of K562 or HEL cells with 1.5 mg/ml of Huangqi (Hex) (Components extracted from Huangqi) for 3-5 d results in the expression of beta-globin gene in both cell lines and leads to terminal differentiation. Moreover, the apoptosis in HEL cells can be induced by increasing concentration of Huangqi (Hex) to 4.5 mg/ml for 3-5 d. Upregulation of Apaf-1, caspase-3 and acetylcholinesterase (AChE) in HEL cells may play a crucial role in the process of apoptosis. The prospect of inducing expression of adult (beta) globin gene and apoptosis selectively in cancer cells is obviously attractive from a therapeutic point of view.

The in vitro reconstitution of nucleosome and its binding patterns with HMG1/2 and HMG14/17 proteins.

Using atomic force microscopy (AFM), the dynamic process of the in vitro nucleosome reconstitution followed by slow dilution from high salt to low salt was visualized. Data showed that the histone octamers were dissociated from DNA at 1M NaCl. When the salt concentration was slowly reduced to 650 mM and 300 mM, the core histones bound to the naked DNA gradually. Once the salt concentration was reduced to 50 mM the classic "beads-on-a-string" structure was clearly visualized. Furthermore, using the technique of the in vitro reconstitution of nucleosome, the mono- and di- nucleosomes were assembled in vitro with both HS2core (-10681 to -10970 bp) and NCR2 (-372 to -194 bp) DNA sequences in the 5 flanking sequence of human b-globin gene. Data revealed that HMG 1/2 and HMG14/17 proteins binding to both DNA sequences are changeable following the assembly and disassembly of nucleosomes. We suggest that the changeable binding patterns of HMG 14/17 and HMG1/2 proteins with these regulatory elements may be critical in the process of nucleosome assembly, recruitment of chromatin-modifying activities, and the regulation of human b-globin gene expression.

Identification of a NF-kappaB site in the negative regulatory element (epsilon-NRAII) of human epsilon-globin gene and its binding protein NF-kappaB p50 in the nuclei of K562 cells.

The developmental control of the human epsilon-globin gene expression is mediated by transcription regulatory elements in the 5' flanking DNA of this gene. Sequence analysis has revealed a DNA motif (GGGGAATTTGCT) similar to NF-kappaB consensus sequence resides in the negative regulatory element (-3028bp approximately -2902bp, termed e-NRAII) 5' to the cap site of this gene. NRF DNA fragment (-3010bp approximately -2986bp) containing the NF-kappaB motif similar sequence was synthesized and used in electrophoresis mobility shift assay (EMSA) and competitive analysis. Data showed that a protein factor from nuclear extracts of K562 cells specifically interacted with NRF DNA fragment. The synthetic NF DNA fragment (containing NF-kappaB consensus sequence) could competed for the protein binding, but MNF DNA fragment (mutated NF-kappaB motif) could not, suggesting that the binding protein is a member of NF-kappaB/Rel family. Western blot assay demonstrated that the molecular weight of NF-kappaB protein in the nuclei of K562 cells is 50ku. We suggested that NF-kappaB p50 may play an important role in the regulation of human epsilon-globin gene expression.

The interaction between the human beta-globin locus control region and nuclear matrix.

Our previous study showed that hydroxyurea (Hu) could induce HEL cells to express human beta-globin gene. However the molecular mechanisms by which the expression of beta-globin gene is activated and regulated are poorly understood. Here we show that the binding patterns between the core DNA sequences (HS2 core sequence -10681 approximately -10971 bp, HS3 core sequence -14991 approximately -14716 bp and HS4 core sequence -18586 approximately -18306 bp) of DNase I hypersensitive sites in the human beta-globin LCR and nuclear matrix proteins isolated from Hu induced and uninduced HEL cells are quite different. Results demonstrated that nuclear matrix proteins might play important roles in regulating the expression of human beta-like globin genes through their interaction with HSs (HS2, HS3 and HS4 core sequences) in the LCR. Moreover, the results obtained from the in vitro DNA-matrix binding assay showed that the core DNA sequences of DNase I hypersensitive sites (HS2, HS3 and HS4) were unable to bind to the nuclear matrix isolated from uninduced HEL cells; in addition, HS2 core DNA sequence was capable of binding to the nuclear matrix prepared from Hu-induced HEL cells, while both HS3 and HS4 core DNA sequences could not do so. Results indicated that the HS2 core DNA sequence may be a functional MAR (matrix attachment region). We suggest that the HS2 core DNA sequence binding to the nuclear matrix in Hu-induced HEL cells may open the structure of chromatin to make the LCR accessible to the promoter of beta-globin gene and to promote its transcription.

Screening of Genes Related to the Expression of Human epsilon-globin Gene by Using Yeast One-hybrid System.

The developmental stage-specific silencing of the human epsilon-globin gene during embryonic period is controlled, in part, by a silencer (from -392 to -177 bp) upstream of this gene. In our previous work, by using DNase I footprinting assay, a major protected region from -278 to -235 bp within this silencer DNA was identified. In order to isolate genes encoding proteins that bind to this target element, a human fetal liver cDNA library was screened by using yeast one-hybrid system. The candidate clones were sequenced, and the ribosomal protein L3 (RPL3) was preliminarily isolated. Electrophoretic mobility shift assay (EMSA) and competition tests also demonstrated its binding activity to the target element. These imply that RPL3 might play an important role in silencing the human embryonic epsilon-globin gene expression through the interaction with this silencer.

Effect of IL-3 on Globin Gene Expression in a Human Erythroleukemia Cell Line.

A human erythroleukemia cell line(K562 cells)was used as a model to study the effect of interleukin-3(IL-3) on human globin gene expression in the cells. The results showed that the beta-globin gene was not expressed in uninduced K562 cells however, it was expressed when K562 cells were induced for 3 or 5 days by IL-3. The expression of alpha- and gamma-globin gene were not much different between IL-3 induced and uninduced K562 cells. Using the method of benzidine-dyeing, it was observed that the percentage of blue cells was significantly increased when K562 cells were induced by IL-3. It suggested that IL-3 could not only activate the exp-ression of beta-globin gene in K562 cells, but also induce the synthesis of hemoglobin. Therefore, IL-3 may play a critical role in inducing K562 cells to terminal differentiation.

Mechanism of Differentiation of HEL Cells Induced by Hydroxyurea.

HEL cells, a human erythroleukemia cell line, mainly express fetal globin gene(gamma) and small amount of the embryonic(epsilon) globin gene, but not the adult (beta) globin gene. Our previous studies demonstrated that hydroxyurea could induce HEL cells to express adult (beta) globin gene and induce HEL cells to terminal differentiation. In order to reveal the differentiation mechanism of HEL cells induced by hydroxyurea, GMSA was performed to examine the binding of nuclear extracts from hydroxyurea induced and uninduced HEL cells to the positive control region in the 5'-flanking sequence of human beta-globin gene and to the synthesized GATA oligonucleotides. Our results showed that, in the nuclear proteins from the induced HEL cells, the binding of GATA-1 to GATA motif was increased. However, the binding of GATA-2 to GATA motif was decreased. Besides, our data showed that a YY1-like protein was decreased quickly in hydroxyurea induced HEL cells. Western blotting analysis was used to analyze variation of GATA proteins in nuclei of HEL cells. Results revealed that the amount of GATA-2 was significantly decreased while the amount of GATA-1 was increased after HEL cells were induced for 12 h. These results indicate that GATA-1 may play a critical role in inducing HEL cells to terminal differentiation. The YY1-like protein and GATA-2 might inhibit HEL cells from terminal differentiation.

Interactions Between HMG proteins and 5'-Flanking cis-Acting Elements of Human epsilon-Globin Gene.

HMG proteins are abundant chromosomal non-histone proteins. It has been shown that HMG proteins play important roles in the structure and function of chromatin. In this work, the binding of HMG proteins to the 5'-Flanking positive and negative regulatory elements of human epsilon-globin Gene gene has been examined by gel mobility shift and DNaseI footprinting assays. Our results demonstrated that HMG proteins 1/2 could bind not only to both positive regulatory elements(-535~-453 bp and -446~-419 bp) but also to the promoter (-177~+1bp) of this gene; however, HMG proteins 14/17 could not bind to those regulatory elements. On the other hand, we also observed that HMG proteins 14/17 could bind to the 5'-flanding silencer(-392~-177 bp) of human epsilon-globin gene, and HMG proteins 1/2 could not bind to that silencer. Our results suggest that HMG proteins might play a critical role in the regulation of the human epsilon-globin gene expression through DNA-protein interactions.

Identification of an Embryonic Erythroid Nuclear Factor Binding to the Positive Stage-specific Regulatory Element of the Human epsilon-Globin Gene.

The erythroid- and developmental stage-specific expression of the human epsilon-globin gene is controlled, in part, by the 5'-flanking DNA sequences of this gene. In the present study, a nuclear transacting factor of molecular weight about 80 kD epsilon-SSP in K562 cell (a human embryonic erythroid cell line) was identified by gel mobility shift assay, DNaseI footprinting assay and Southwestern blot assay. It could specifically bind to a positive stage-specific regulatory element (-446 bp to -419 bp, termed epsilon-PREII) of the human epsilon-globin gene. Our data suggested that this nuclear factor (termed epsilon-SSP) might be an erythroid- and stage-specific protein. In addition, we observed that the shift band of this protein bound with the epsilon-PREII could be competed by DNA fragments derived from the human epsilon-globin gene promoter(-177 bp to +1 bp), the DNaseI hypersensitive site 2 (-10 965 bp to -10 681 bp) and the hypersensitive site 3(-14 993 bp to -14 718 bp) of beta-LCR, suggesting that epsilon-SSP might be involved in the developmental regulation of human epsilon-globin gene through the interaction between the proximal (promoter) and the distal (LCR) cis-acting elements.