Activation of heat shock factor 2 during hemin-induced differentiation of human erythroleukemia cells.
Hemin induces nonterminal differentiation of human K562 erythroleukemia cells, which is accompanied by the expression of certain erythroid cell-specific genes, such as the embryonic and fetal globins, and elevated expression of the stress genes hsp70, hsp90, and grp78/BiP. Previous studies revealed that, as during heat shock, transcriptional induction of hsp70 in hemin-treated cells is mediated by activation of heat shock transcription factor (HSF), which binds to the heat shock element (HSE). We report here that hemin activates the DNA-binding activity of HSF2, whereas heat shock induces predominantly the DNA-binding activity of a distinct factor, HSF1. This constitutes the first example of HSF2 activation in vivo. Both hemin and heat shock treatments resulted in equivalent levels of HSF-HSE complexes as analyzed in vitro by gel mobility shift assay, yet transcription of the hsp70 gene was stimulated much less by hemin-induced HSF than by heat shock-induced HSF. Genomic footprinting experiments revealed that hemin-induced HSF and heat shock-induced HSF, HSF2, and HSF1, respectively, occupy the HSE of the human hsp70 promoter in a similar yet not identical manner. We speculate that the difference in occupancy and/or in the transcriptional abilities of HSF1 and HSF2 accounts for the observed differences in the stimulation of hsp70 gene transcription.
Sistonen
L
L
Department of Biochemistry, Molecular Biology, and Cell Biology, Northwestern University, Evanston, Illinois 60208.
Sarge
K D
KD
Phillips
B
B
Abravaya
K
K
Morimoto
R I
RI
D001483:Base Sequence; D002454:Cell Differentiation / Q000235:genetics*; D004247:DNA / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D005786:Gene Expression Regulation; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006427:Hemin / Q000502:physiology*; D006358:Hot Temperature; D006801:Humans; D007700:Kinetics; D004915:Leukemia, Erythroblastic, Acute; D008969:Molecular Sequence Data; D011485:Protein Binding; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D014157:Transcription Factors; C070389:HSF2 protein, human; D006427:Hemin; D004247:DNA