Inhibition of heme synthesis induces apoptosis in human erythroid progenitor cells

Abstract

Heme synthesis by erythroid progenitor cells is maintained by erythropoietin (EP), insulin-like growth factor-I (IGF-I), and stem cell factor (SCF), and without these growth factors apoptosis (programmed cell death) occurs. To clarify the possible interaction between heme synthesis and programmed cell death of human erythroid progenitor cells, the effect of specific inhibition of heme synthesis on apoptosis of highly purified human erythroid colony forming cells (ECFC) was studied. When the amount of uncleaved DNA was determined as a measure of apoptosis, the heme synthesis inhibitors, succinylacetone (SA) (0.1 mmol/L) or isonicotinic acid hydrazide (INH) (10 mmol/L), significantly decreased the amount of uncleaved DNA (P < 0.01) in the presence of erythropoietin (EP). Addition of recombinant heavy-chain ferritin (rHF) (10 nmol/L), or deprivation of transferrin from the culture medium, which decreased heme synthesis, also reduced the amount of uncleaved DNA (P < 0.01). The production of apoptosis by diverse inhibitors of heme synthesis was in each case reversed by the addition of hemin (0.1 mmol/L) and did not occur with HL-60 cells. When the colony-forming capacity of ECFC was determined by plasma clot assay, SA, INH, or rHF reduced the number of CFU-E (P < 0.01), and the effect of SA was reversed by hemin. The addition of SA did not alter the c-myc response of ECFC to EP. These data indicate that inhibition of heme synthesis induces apoptosis of human erythroid progenitor cells, in a manner independent of an early c-myc response, and suggest that the presence of apoptosis in ineffective erythropoiesis may be secondary to impaired heme synthesis.

Transcription factor GATA-1 permits survival and maturation of erythroid precursors by preventing apoptosis.

“…Although erythroid cGSHPX gene expression is regulated by GATA-binding sites in a 3' enhancer (33), cGSHPX mRNA levels are equivalent in wild-type and GATA-1-proerythroblasts (unpublished data). Finally, inhibition of heme synthesis in erythroid precursors can result in apoptosis (34). The genes encoding the heme biosynthetic enzymes porphobilinogen deaminase (35,36) and ferrochelatase (37) GATA-1 appears to negatively regulate GATA-2 during normal erythropoiesis (5).…”

Adaptation of the endothelium to fluid flow: in vitro analyses of gene expression and in vivo implications

“…107¡111 The observed shearinduced downregulation of the transferrin receptor and the upregulation of ferritin heavy and light chains may suppress oxidative stress-related endothelial apoptosis by scavenging iron radicals. 69,70,112,113 TG F b and its signaling pathway appear to abrogate apoptosis as well. TGF b1, Smad6, Smad8 and the immediate early gene SG K are signi cantly upregulated by LSS, and are known to inhibit apoptosis in some contexts while the potentially proapoptotic growth factor BMP4 is downregulated by LSS in vitro.…”

Heme oxygenase 1 is expressed in murine erythroid cells where it controls the level of regulatory heme

“…Additionally, our finding of elevated apoptosis in MELHO-1 cells is congruent with an earlier report that the inhibition of heme synthesis induces apoptosis in human erythroid progenitor cells. 48 Also, membranes of b-thalassemic erythrocytes, 49,50 and likely also erythroblasts, contain iron-a substrate for a Fenton reaction-that can be derived from heme because of the enhanced activity of HO-1.…”