A 5′ untranslated region containing the IRES element in the Runx1 gene is required for angiogenesis, hematopoiesis and leukemogenesis in a knock-in mouse model

Abstract

Although internal ribosome entry site (IRES)-mediated translation is considered important for proper cellular function, its precise biological role is not fully understood. Runx1 gene, which encodes a transcription factor implicated in hematopoiesis, angiogenesis, and leukemogenesis, contains IRES sequences in the 5' untranslated region. To clarify the roles of the IRES element in Runx1 function, we generated knock-in mice for either wild-type Runx1 or Runx1/Evi1, a Runx1 fusion protein identified in human leukemia. In both cases, native promoter-dependent transcription was retained, whereas IRES-mediated translation was eliminated. Interestingly, homozygotes expressing wild-type Runx1 deleted for the IRES element (Runx1(Delta IRES/Delta IRES)) died in utero with prominent dilatation of peripheral blood vessels due to impaired pericyte development. In addition, hematopoietic cells in the Runx1(Delta IRES/Delta IRES) fetal liver were significantly decreased, and exhibited an altered differentiation pattern, a reduced proliferative activity, and an impaired reconstitution ability. On the other hand, heterozygotes expressing Runx1/Evi1 deleted for the IRES element (Runx1(+/RE Delta IRES)) were born normally and did not show any hematological abnormalities, in contrast that conventional Runx1/Evi1 heterozygotes die in utero with central nervous system hemorrhage and Runx1/Evi1 chimeric mice develop acute leukemia. The findings reported here demonstrate the essential roles of the IRES element in Runx1 function under physiological and pathological conditions.

Identification of RUNX1 as a Mediator of Aberrant Retinal Angiogenesis

“…RUNX proteins have pleiotropic functions in vascular development, hematopoiesis, and cancer through direct transcriptional regulation of target genes and complex interactions with fundamental signaling mechanisms including Notch and transforming growth factor-β pathways (21,22). RUNX1 is a major contributor to cancer progression and metastasis, most notably in acute myeloid leukemia, and also plays a role in angiogenesis (18,23–26). …”

Novel function of PITH domain-containing 1 as an activator of internal ribosomal entry site to enhance RUNX1 expression and promote megakaryocyte differentiation

“…The IRES element in the Runx1 gene is required for angiogenesis, hematopoiesis and leukemogenesis in Runx1 knockin mice deleted for IRES element [10]. To demonstrate the role of PITHD1 in megakaryopoiesis, mouse fetal liver cells were transduced with control lentiviral vector (Ctrl) or PITHD1-overexpressing (PITHD1) vector for megakaryocyte culture.…”

“…GATA1 expression served as control. *Indicates significance (p \ 0.05) Novel function of PITHD1 829 [10]. For instance, the RUNX1 knockin mice deleted for IRES element mimicked some features of RUNX1-deficient mice.…”

“…Instead, P2-UTR contains an internal ribosome entry site (IRES) element that is critical for translation of RUNX1a/b [7]. P1-UTRdependent RUNX1 expression is not required for embryonic survival but affects hematopoietic development while P2-UTR-dependent RUNX1 expression is critical for definitive hematopoiesis, leukemogenesis, angiogenesis, thymic development, and postnatal survival [10]. These findings highlight the necessity of tight control of RUNX1 expression and the pivotal role of IRES element in RUNX1 regulation.…”

Runx1 contributes to neurofibromatosis type 1 neurofibroma formation

“…13,14 Runx1 is important for neuronal development and glial cell differentiation. 15–17 Runx1 gene is expressed in proliferating Mash1 + or NeuroD + olfactory receptor neuron progenitors on the basal side of the olfactory epithelium.…”