Hsp70 regulates erythropoiesis by preventing caspase-3-mediated cleavage of GATA-1

Abstract

Caspase-3 is activated during both terminal differentiation and erythropoietin-starvation-induced apoptosis of human erythroid precursors. The transcription factor GATA-1, which performs an essential function in erythroid differentiation by positively regulating promoters of erythroid and anti-apoptotic genes, is cleaved by caspases in erythroid precursors undergoing cell death upon erythropoietin starvation or engagement of the death receptor Fas. In contrast, by an unknown mechanism, GATA-1 remains uncleaved when these cells undergo terminal differentiation upon stimulation with Epo. Here we show that during differentiation, but not during apoptosis, the chaperone protein Hsp70 protects GATA-1 from caspase-mediated proteolysis. At the onset of caspase activation, Hsp70 co-localizes and interacts with GATA-1 in the nucleus of erythroid precursors undergoing terminal differentiation. In contrast, erythropoietin starvation induces the nuclear export of Hsp70 and the cleavage of GATA-1. In an in vitro assay, Hsp70 protects GATA-1 from caspase-3-mediated proteolysis through its peptide-binding domain. The use of RNA-mediated interference to decrease the Hsp70 content of erythroid precursors cultured in the presence of erythropoietin leads to GATA-1 cleavage, a decrease in haemoglobin content, downregulation of the expression of the anti-apoptotic protein Bcl-X(L), and cell death by apoptosis. These effects are abrogated by the transduction of a caspase-resistant GATA-1 mutant. Thus, in erythroid precursors undergoing terminal differentiation, Hsp70 prevents active caspase-3 from cleaving GATA-1 and inducing apoptosis.

The transcription factor GATA-1 is overexpressed in breast carcinomas and contributes to survivin upregulation via a promoter polymorphism

“…GATA-1 cleavage by caspase-8 was proposed to have an important role in the negative control of erythropoiesis (De Maria et al, 1999)), whereas GATA-1 was protected from differentiation-associated activation of caspase-3 by interaction with HSP70 (Ribeil et al, 2007). HSP70 expression is increased in breast carcinomas (Ciocca and Calderwood, 2005) and could protect GATA-1 from degradation in transformed cells when caspases are activated.…”

Interaction of heat-shock protein 90β isoform (HSP90β) with cellular inhibitor of apoptosis 1 (c-IAP1) is required for cell differentiation

“…As an E3 ligase, c-IAP1 could favour the degradation of specific proteins. Caspases have been reported to be ubiquitinated by mammalian IAPs in vitro but the role of these enzymes in cell differentiation is limited to specific cell types 33,34 and evidence that IAPs physiologically ubiquitinylate caspases and promote their degradation, is still missing. 32 c-IAP1 could also modulate NF-kB transcription factor activity 9 or specific signalling pathways involving adaptor molecules such as TRAF2 7 and serine-threonine kinases such as ASK1.…”

No death without life: vital functions of apoptotic effectors

“…acinus), but spares other potential substrates (such as the major erythroid transcription factor GATA-1), presumably Day jobs of night killers L Galluzzi et al because these proteins are protected by the interaction with HSP70. 19,20 Interestingly, it has been suggested that caspase-3 involvement in erythropoiesis is restricted to the early phases of proerythroblast differentiation, with no major roles in the nuclear substructure reorganization and nuclear extrusion that characterize the late phases of the process. 21 Caspase activation is also involved in thrombopoiesis.…”