Contrasting dynamic responses in vivo of the Bcl-xL and Bim erythropoietic survival pathways

Abstract

Survival signaling by the erythropoietin (Epo) receptor (EpoR) is essential for erythropoiesis and for its acceleration in hypoxic stress. Several apparently redundant EpoR survival pathways were identified in vitro, raising the possibility of their functional specialization in vivo. Here we used mouse models of acute and chronic stress, including a hypoxic environment and ␤-thalassemia, to identify two markedly different response dynamics for two erythroblast survival pathways in vivo. Induction of the antiapoptotic proteinBcl-x L is rapid but transient, while suppression of the proapoptotic protein Bim is slower but persistent. Similar to sensory adaptation, however, the Bcl-x L pathway "resets," allowing it to respond afresh to acute stress superimposed on a chronic stress stimulus. Using "knockin" mouse models expressing mutant EpoRs, we found that adaptation in the Bcl-x L response occurs because of adaptation of its upstream regulator Stat5, both requiring the EpoR distal cytoplasmic domain. We conclude that survival

miR-214 protects erythroid cells against oxidative stress by targeting ATF4 and EZH2

“…Bim is a crucial downstream determinant in regulating cell viability and survival, and previous studies have demonstrated that Bim is a potent pro-apoptotic protein in initiating the intrinsic apoptotic pathway under both physiological and pathological conditions [76,77]. Bim level was also regulated by erythropoietin (EPO)-mediated signaling in order to sustain the survival of erythroid cells [78,79]. Nevertheless, there is still no report on the implication of Bim alterations in regulating erythroid cells survival through miRNAs dependent manner to date.…”

Emerging EPO and EPO receptor regulators and signal transducers

“…67 Koulnis et al have described EPO's slow yet persistent down-modulation of proapoptotic Bcl2-like 11 (Bim) in murine splenic EPCs. 68 Prior studies in HCD57 cells and primary murine EPCs also demonstrated EPOinduced Bim phosphorylation and proteasomal degradation. 69 The inhibition of Bim therefore represents one EPO-induced EPC survival mechanism.…”

“…69 The inhibition of Bim therefore represents one EPO-induced EPC survival mechanism. Post-EPO dosing, Bcl-xL levels in splenic EPCs transiently increase, 68 and in 32D-EPOR cells Bcl-xL is an EPO/ EPOR/STAT5 target gene. 70 These latter EPO effects, however, are not observed in erythroid colony-forming unit-like murine BM EPCs, 71 and EPO can efficiently cytoprotect Bclx-KO EPCs.…”

Isocitrate ameliorates anemia by suppressing the erythroid iron restriction response

“…Differentiation of human erythroid progenitors was assessed by costaining cells with fluorochrome-conjugated antibodies to CD34 (a marker of immaturity), CD36 (an early marker of erythroid lineage commitment) (37), and glycophorin A (GPA) (a later marker of erythroid differentiation). Intracellular staining for erythroid PU.1 expression followed the guidelines of Koulnis et al (56). Specifically, human progenitors stained for CD34, CD36, and GPA underwent fixation and permeabilization using the BD Cytofix/Cytoperm Perm/Wash kit (BD Biosciences), followed by staining in the Perm/Wash solution with Alexa Fluor 488 rabbit anti-PU.1 antibody or matched control antibody (Cell Signaling Technology).…”