Concomitant inactivation of Rb and E2f8 in hematopoietic stem cells synergizes to induce severe anemia

Abstract

The retinoblastoma (Rb) tumor suppressor plays important roles in regulating hematopoiesis, particularly erythropoiesis. In an effort to understand whether Rb function can be mediated by E2F transcription factors in a BM-derived hematopoietic system in mice, we uncovered a functional synergy between Rb and E2F8 to promote erythropoiesis and to prevent anemia. Specifically, whereas Mx1-Cre-mediated inactivation of Rb or E2f8 in hematopoietic stem cells only led to mild erythropoietic defects, concomitant inactivation of both genes resulted in marked ineffective erythropoiesis and mild hemolysis, leading to severe anemia despite the presence of enhanced extramedullary erythropoiesis. Interestingly, although ineffective erythropoiesis was already present in the Rb ⌬/⌬ mice and exacerbated in the Rb ⌬/⌬ ;E2f8 ⌬/⌬ mice, hemolysis was exclusively manifested in the double-knockout mice. Using an adoptive transfer system and an erythroidspecific knockout system, we have shown that the synergy of Rb and E2f8 deficiency in triggering severe anemia is intrinsic to the erythroid lineage. Surprisingly, concomitant inactivation of Rb and E2f7, a close family member of E2f8, did not substantially worsen the erythropoietic defect resulted from Rb deficiency. The results of the present study reveal the specificity of E2F8 in mediating Rb function in erythropoiesis and suggest critical and overlapping roles of Rb and E2f8 in maintaining normal erythropoiesis and in preventing hemolysis. (Blood.

Inactivation of Rb and E2f8 Synergizes To Trigger Stressed DNA Replication during Erythroid Terminal Differentiation

“…1A and B). These data are consistent with our previous finding that inactivation of E2f8 alone had virtually no effect on erythropoiesis (12). In addition, gene expression profiles for the Rb KO mice and the Rb;E2f8 double-KO (DKO) mice were also similar, although there were greater gene expression changes in the DKO mice than in the Rb KO mice (Fig.…”

“…In addition, inactivation of Rb specifically in hematopoietic stem cells (HSC) or the erythroid lineage leads to mild anemia and mild splenomegaly (11)(12)(13)(14). Interestingly, while the role of Rb in the control of postnatal erythropoiesis is cell autonomous (12,13), Rb appears to elicit both cell-autonomous and non-cell-autonomous signals to maintain normal erythropoiesis during embryogenesis (10,15,16). These data suggest that Rb may make different contributions to embryonic erythropoiesis and postnatal erythropoiesis.…”

“…Consistent with an important role of cell cycle control in erythroid terminal differentiation and erythropoiesis, Rb knockout (KO) embryos are anemic (6)(7)(8), a defect that can be suppressed by a functionally normal placenta (9,10). In addition, inactivation of Rb specifically in hematopoietic stem cells (HSC) or the erythroid lineage leads to mild anemia and mild splenomegaly (11)(12)(13)(14). Interestingly, while the role of Rb in the control of postnatal erythropoiesis is cell autonomous (12,13), Rb appears to elicit both cell-autonomous and non-cell-autonomous signals to maintain normal erythropoiesis during embryogenesis (10,15,16).…”

“…We recently uncovered a surprising functional interaction between Rb and E2F8 in the erythroid lineage (12). Specifically, while the inactivation of Rb or E2f8 in HSC or the erythroid lineage led to mild erythropoietic defects, the concomitant inactivation of both genes synergized to trigger severe anemia, which is characterized by profound ineffective erythropoiesis and mild hemolysis.…”

Involvement of atypical transcription factor E2F8 in the polyploidization during mouse and human decidualization

“…14,15 Several studies have associated atypical E2Fs in cell proliferation, differentiation and apoptosis, embryo development, angiogenesis, polyploidization of hepatocytes and trophoblast giant cells (TGC) and tumorigenesis. 7,9,[16][17][18][19][20][21][22][23] However, the expression, regulation and function of atypical E2Fs in mouse uterus during early pregnancy are still unknown.…”