UNIVERSITY OF MALTA
RESEARCH SEMINARS
Abstract form
Title: The Regulation of mRNA translation controls the balance
between expansion and differentiation of erythroid progenitors.
Presenter: Godfrey Grech B.Sc., M.Phil.
Contact address: Erasmus MC, Department of Hematology, Rotterdam
Tel: 0031 010 408 8300
Fax:
Email: g.grech@erasmusmc.nl
Presentation date: 15th November 2004
(approximately 200-250 words)
Abstract
Erythroid progenitors can be expanded in vitro in the presence of erythropoietin
(Epo), stem cell factor (SCF) and dexamethasone, while they differentiate to
enucleated erythrocytes in presence of Epo only. Our study aims to identify (i)
signalling pathways that control expansion of erythroid progenitors and (ii) genes
regulated by these signalling pathways. Since SCF strongly activates
phosphotidylinositol 3 kinase (PI3K) and inhibition of PI3K with LY294002 induces
terminal differentiation of erythroid progenitors under Epo and SCF stimulation, SCF
seems to enhance renewal divisions of erythroid progenitors via a PI3K-dependent
mechanism. An important PI3K-dependent mechanism is the regulation of capbinding factor eIF4E (eukaryotic Initiation Factor 4E), a rate limiting step in
translation initiation. We show that moderate overexpression of eIF4E (up to 2-fold)
markedly delays Epo-induced differentiation and allows for an increased number of
renewal divisions instead. This data suggests that mRNAs with a structured
untranslated region (UTR), that are only efficiently translated at optimal eIF4E
levels, contribute to maintain proliferation of hematopoietic progenitors. To identify
the genes whose expression is regulated by signalling-induced polysome
recruitment, we analysed gene-expression profiles on micro-arrays, in which we
compared total and polysome-bound mRNA from factor deprived and Epo plus SCF
restimulated erythroid progenitors. A selection of candidate gene transcripts were
validated by RT-PCR. Polysome recruitment of 10 transcripts tested so far,
appeared to be PI3K dependent. In conclusion, we have demonstrated that
regulation of translation initiation by eIF4E is an important pathway stimulated by
SCF to delay differentiation and to maintain expansion of erythroid progenitors. We
identified gene-transcripts of which polysome recruitment is regulated by SCFinduced PI3K/PKB activity. Currently we are evaluating the role of selected genes
involved in signal transduction mechanisms and DNA binding, in the control of
expansion and differentiation of erythroid progenitors.