Function of GATA transcription factors in hydroxyurea-induced HEL cells

HEL cells, a human erythroleukemia cell line, mainly express the fetal (r)globin gene and trace amount of the embryonic (E)globin gene, but not adult (B) globin gene. Here we show that hydroxyurea (HU) can induce HEL cells to express adult (B) globin gene and lead these cells to terminal differentiation. Results showed in Gel mobility shift assays that GATA factors could specifically bind to the regulatory elements of human B- globin gene, including the proximal regulatory element (the B- promoter) and the distal regulatory elements (the DNase I hypersensitive sites in the LCR, HS2-HS4 core sequences). However, the DNA binding patterns of GATA factors were quite different between HU-induced and uninduced HEL cells. Western-blot analysis of nuclear extracts from both the uninduced and HU- induced HEL cells revealed that the level of GATA-2 transcription factor decreased, whereas the level of GATA-1 transcription factor increased following the time of hydroxyurea induction. Furthermore, using RT-PCR analysis the expression of human B-globin gene in HU-induced HEL cells could be blocked again when HEL cells were incubated in the presence of antisense oligonucleotides for hGATA-1, suggesting that the upregulation of hGATA-1 transcription factor might be critical for the expression of human β- globin gene in HU-induced HEL cells.

The apoptosis of HEL cells induced by hydroxyurea

Hydroxyurea has been used to synchronize cultured cells to S-phase and used to treat patients with sicklecell anemia. Recently, we found that hydroxyurea can induce the apoptosis of HEL (human erythroleukemia) cells.The induced HEL cells showed ultrastructurally chromatin condensation with regular crescents at the nuclear edges and apoptotic bodies. However, the cells of K562, another human erythroleukemia cell line, did not show such morphological changes. Under fluoroscope, the HEL cells after induction often displayed a clear reduction in nuclear diameter and nuclear chromatin cleavage and condensation and the presence of nuclear ring and apoptotic bodies. Analysis with flow cytometry showed that the percentage of apoptotic cells is about 30-40% after HEL cells were induced by hydroxyurea for 3 days. DNA ladder can be observed by electrophoretic analysis.

STAT1 is involved in signal transduction in the EPOinduced HEL cells

Erythropoietin (EPO) is the ma jor regulator of mammalian erythropoisis, which stimulates the growth and differentiation of hematopoietic cells through interaction with its receptor (EPO-R). Here we use HEL cells (a human erythro-leukemia cell line) as a model to elucidate the pathway of signal transduction in the EPO-induced HEL cells. our data show that the EPOR (EPO receptor) on the surface of HEL cells interacts with the Janus tyrosine protein kinase (Jak2) to transduce intracellular signals through phosphorylation of cytoplasmic proteins in EPO-treated HEL cells. Both STAT1 and STAT5 in this cell line are tyrosine-phosphorylated and translocated to nucleus following the binding of EPO to HEL cells.Furthermore, the binding of both STAT1 and STAT5 proteins to specific DNA elements (SIE and PIE elements) is revealed in an EPO-dependent manner. Our data demonstrate that the pathway of signal transduction following the binding of EPO to HEL cells is similar to immature erythroid cell from the spleen of mice infected with anemia strain of Friend virus.

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

Our previous study showed that hydroxyurea (Hu) could induce HEL cells to express humanβ-globin gene. However the molecular mechanisms by which the expression of β-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- -10971 bp , HS3 core sequence -14991- -14716 bp and HS4 core sequence -18586- -18306 bp) of DNase I hypersensitive sites in the human β-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 humanβ-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 β-globin gene and to promote its transcription.

Effect of Sargassum fusiforme polysaccharide on apoptosis and its possible mechanism in human erythroleukemia cells

This study aimed to investigate the effects of Sargassum fusiforme polysaccharide(SFPS I,II,and III)on the apoptosis and regulation of human erythroleukemia(HEL)cells.The effect of different doses of SFPS on HEL cell growth was detected using the Cell Counting Kit-8 method,and apoptosis was detected by Hoechst staining.Cell cycle distribution and apoptosis were detected using flow cytometry.Expression of the cell cycle gene,p53,antiapoptotic genes,Bcl-xL and Bcl-2,and pro-apoptotic genes,Bax,Bad,and Caspase-3,as well as the expression of the corresponding proteins,were detected using real-time quantitative polymerase chain reaction(qPCR)and Western blot.The results showed that SFPS Ⅱ and Ⅲ decreased HEL cell viability and induced HEL cell apoptosis.Different concentrations of SFPS(Ⅰ,Ⅱ,and Ⅲ)were detected that induced much less toxic effect in normal human embryonic lung(MRC-5)cells,and SFPS Ⅰ increased cell proliferation,indicating its favorable selectivity towards cancer cells.The mechanism by which SFPS induced apoptosis was also found to be related to the induction of cell cycle arrest in the G0/G1 phase and the increased expression of apoptosis-related genes and proteins.We concluded that SFPS induces HEL cell apoptosis,possibly via activation of the Caspase pathway,providing the theoretical basis for the development of SFPS-based anti-tumor drug products.