C-terminal cleavage of human Foxp3 at a proprotein convertase motif abrogates its suppressive function.

Foxp3 plays a critical role in the development and function of regulatory T cells (Tregs). Differences in translational and post-translational processing of murine and human Foxp3 have been recently reported. Human Foxp3 exists as four isoforms generated by alternative splicing. Mouse Foxp3 only exists as one isoform, but can be proteolytically cleaved by N-terminal and/or C-terminal proprotein convertase subtilisin/kexins (PCSKs). Here, we show by transcriptome analysis that the proprotein convertases PCSK7, PCSK5 and Furin are present in human CD4(+) T cells with different expression patterns. Notably, after in vitro activation, only PCSK7 and Furin are expressed in Tregs and T effector cells (Teffs), with overexpression of PCSK7 in Tregs compared to Teffs. Human Foxp3 protein displays specific motifs that can be potentially cleaved by convertases. Consequently, we transduced human CD4(+) cells with Foxp3-expressing lentiviral vectors and assessed the generation of proteolytically cleaved Foxp3 forms by Western blot. Three different Foxp3 forms were detected, indicating that human Foxp3 can also be subjected to proteolytic cleavage at the N-terminal and C-terminal ends. These results prompted us to assess the suppressive activity associated with each forms. We observed that full length and N-cleaved Foxp3-transduced CD4(+) T cells similarly suppressed the in vitro proliferation of Teffs. However, the C-cleaved or N&C-cleaved Foxp3 forms afforded almost no suppressive function, indicating a crucial role of the human Foxp3 C-terminal region in Tregs suppressive activity, in marked contrast with the report of a superior suppressive activity for the C-cleaved murine Foxp3 compared to the full length.

[From teaching and care to creativity, a therapeutic stay project]. / De l'enseignement et du soin à la créativité, un projet de séjour thérapeutique.

A group of young patients led by teachers and caregivers decided to organise a therapeutic stay. The objective of the stay was to visit historical sites to act out scenes from a fictional play written in a workshop. This stay enabled patients to develop their autonomy and strengthened the therapeutic alliance.

Megakaryocyte growth and development factor-induced proliferation and differentiation are regulated by the mitogen-activated protein kinase pathway in primitive cord blood hematopoietic progenitors.

In several erythroleukemia cell lines, activation of mitogen-activated protein kinases (MAPK) by phorbol esters or megakaryocyte growth and development factor (MGDF) is required for induction of megakaryocytic phenotype and growth arrest. To support this model, we have examined the effect of a specific inhibitor of this pathway (PD98059) on human CD34(+) hematopoietic progenitors isolated from cord blood (CB), induced to differentiate along the megakaryocytic lineage in liquid cultures supplemented with rhuMGDF. RhuMGDF induced a sustained activation of MAPK in megakaryocytes and this activation was completely inhibited in the presence of low concentrations of PD98059 (6 to 10 micromol/L). At this concentration, PD98059 induced an increase in cell proliferation, resulting in accumulation of viable cells and a prolongation of the life time of the cultures. This increase correlated with an increase in DNA synthesis rather than with a reduction in apoptosis. This effect was combined with developmental changes indicative of delayed megakaryocytic differentiation: (1) PD98059-treated cells tended to retain markers of immature progenitors as shown by the increased proportion of both CD34(+) and CD41(+)CD34(+) cells. (2) PD98059-treated cultures were greatly enriched in immature blasts cells. (3) PD98059 increased megakaryocytic progenitors able to form colonies in semisolid assays. Thus, the MAPK pathway, although not required for megakaryocyte formation, seems to be involved in the transition from proliferation to maturation in megakaryocytes. Inhibition of MAPK activation also led to an increase in the number and size of erythroid colonies without affecting granulocyte/macrophage progenitor numbers suggesting that, in addition to the megakaryocytic lineage, the MAPK pathway could play a role in erythroid lineage differentiation.