Erythropoieses

Project leaders: Emile van den Akker PhD and Marieke von Lindern PhD

Expansion of erythroid progenitors is critically dependent on the presence of Epo and SCF. We developed an in vitro cell system in which erythroid progenitors can be expanded in presence of Epo, SCF and glucocorticoids, while retaining the capacity to undergo complete and synchronous differentiation to mature erythrocytes. In this model system we address the following issues:

Erythropoiesis_Epo_SCF

The role of selective mRNA translation in control of proliferation and differentiation of erythroid progenitors

We observed that SCF-induced activation of the PI3K-mTOR-eIF4E pathway is critical and sufficient to inhibit erythroid differentiation. This pathway is particularly important to translate transcripts with a complex RNA structure. We identified several transcripts that encode proteins controlling proliferation and differentiation of erythroblasts, and sensitive to PI3K-mTOR-eIF4E.

We studied regulation and function of two proteins in more detail. 1. Igbp1 or the alpha4 regulatory subunit of protein phosphatase 2A (Pp2A). Pp2A dephosphorylates the mTOR targets S6kinase and eIF4E. The alpha4 subunit inhibits this activity and thereby enhances mTOR signaling.

Use1: Unusual Snare in the ER. Use1 is involved in retrograde transport of proteins from the Golgi to the ER (i.g. transport receptors and chaperones). The use1 N-terminal domain binds a tethering complex associated with incoming vesicles from the Golgi. Translation of Use1 increases upon activation of the PI3K-mTOR-eIF4E pathway. The presence of upstream open reading frames in the 5’UTR renders Use1 translation sensitive to stress factors such as lack of haem, or unfolded proteins in the ER. Such stress results in the translation a protein that lacks the N-terminal interaction domain and may act as a dominant negative protein.

Erythropoiesis_mRNA

Impaired mRNA translation in anemia

Although PI3K-mTOR activity also controls ribogenesis, we found that ribosome diseases such as DBA (Diamond-Blackfan Anemia) and SBDS (Shwachman-Bodian-Diamond Syndrome) affect translation of distinct sets of transcripts. Again we found that a selective set of transcripts is poorly translated in DBA models and erythroblasts cultured from peripheral blood of DBA patients. In case of DBA our results indicate impaired translation initiation from an IRES (internal ribosomal entry site).

Again we focus on our studies on the regulation and function of two proteins:

  1. Bag1: Bcl2 associated athanogene, a cochaperone of Hsp70/Hsc70.
  2. Csde1: cold shock domain-containing protein E1, an RNA binding protein that is itself involved in control of mRNA translation.

Key publications