Biomedical subjects

Michaëla Fontenay

Publications and source records attributed to Michaëla Fontenay.

5 recordsLinked to original sources

PubMed2006

Caspase-8 prevents sustained activation of NF-kappaB in monocytes undergoing macrophagic differentiation.

Caspases have demonstrated several nonapoptotic functions including a role in the differentiation of specific cell types. Here, we show that caspase-8 is the upstream enzyme in the proteolytic caspase cascade whose activation is required for the differentiation of peripheral-blood monocytes into macrophages. On macrophage colony-stimulating factor (M-CSF) exposure, caspase-8 associates with the adaptor protein Fas-associated death domain (FADD), the serine/threonine kinase receptor-interacting protein 1 (RIP1) and the long isoform of FLICE-inhibitory protein FLIP. Overexpression of FADD accelerates the differentiation process that does not involve any death receptor. Active caspase-8 cleaves RIP1, which prevents sustained NF-kappaB activation, and activates downstream caspases. Together these data identify a role for caspase-8 in monocytes undergoing macrophagic differentiation, that is, the enzyme activated in an atypical complex down-regulates NF-kappaB activity through RIP1 cleavage.

Caspase 8↗

PubMed2006

Identification of proteins cleaved downstream of caspase activation in monocytes undergoing macrophage differentiation.

We have shown previously that caspases were specifically involved in the differentiation of peripheral blood monocytes into macrophages while not required for monocyte differentiation into dendritic cells. To identify caspase targets in monocytes undergoing macrophagic differentiation, we used the human monocytic leukemic cell line U937, whose macrophagic differentiation induced by exposure to 12-O-tetradecanoylphorbol 13-acetate (TPA) can be prevented by expression of the baculovirus caspase-inhibitory protein p35. A comparative two-dimensional gel proteomic analysis of empty vector- and p35-transfected cells after 12 h of exposure to 20 nm TPA, followed by mass spectrometry analysis, identified 38 differentially expressed proteins. Those overexpressed in p35-expressing cells (n = 16) were all full-length, whereas half of those overexpressed in control cells (n = 22) were N- or C-terminal cleavage fragments. The cleavage or degradation of seven of these proteins was confirmed in peripheral blood monocytes undergoing macrophage colony-stimulating factor-induced macrophagic differentiation. In U937 cells exposed to TPA, these proteolytic events can be inhibited by expression of a caspase-8 dominant negative mutant or the cowpox virus CrmA caspase inhibitor. These cleavages provide new insights to analyze the role of caspases in this specific differentiation program.

Carcinogens↗

PubMed2006

Erythropoiesis abnormalities contribute to early-onset anemia in patients with septic shock.

RATIONALE: The intimate mechanisms of early onset anemia observed in critically ill patients with septic shock remain unclear. OBJECTIVES: We investigated erythropoiesis abnormalities in this setting by studying morphologic, functional, and biochemical patterns of erythroid lineage. METHODS: Erythroid lineage in the bone marrow from patients with septic shock who developed early-onset anemia was compared with that of healthy control subjects. Survival and proliferation capacities were quantified in both groups. Biochemical and flow cytometry patterns of apoptosis were dissected by exploring antiapoptotic (erythropoietin [Epo] receptor-dependent) and proapoptotic (death receptor-dependent) pathways. MEASUREMENTS AND MAIN RESULTS: Erythroid lineage was morphologically similar in both groups. Apoptosis of glycophorin-A-positive erythroid precursors was increased in patients versus control subjects as assessed by labeling with annexin V (26.1 +/- 8.8 vs. 3.1 +/- 2.9%, p < 0.05) or 3-3'-dihexyloxacarbocyanine iodide (55.9 +/- 10.5 vs. 19.1 +/- 5.4%, p < 0.05), respectively. This was associated with significant overexpression of Fas on erythroid precursors and higher tumor necrosis factor-alpha plasma levels in patients with septic shock vs. control subjects. Moreover, growth capacities of late erythroid progenitors of burst-forming unit erythroids (BFU-Es) at Day 10 were impaired in the presence of serum from patients with septic shock as compared with the effect of serum from control subjects (27 +/- 12 vs. 109 +/- 27 per 10(5) seeded cells, respectively; p < 0.001). Saturating concentrations of recombinant human Epo (rHuEpo) restored growth capacity of patients' BFU-Es (72 +/- 14 per 10(5) seeded cells) in autologous conditions of serum. CONCLUSIONS: Early-onset anemia that may be observed in patients with septic shock is associated with defective erythropoiesis related to an excess of apoptosis that can be counterbalanced in vitro by rHuEpo.

Adult↗

PubMed2005

Vital functions for lethal caspases.

Caspases are a family of cysteine proteases expressed as inactive zymogens in virtually all animal cells. These enzymes play a central role in most cell death pathways leading to apoptosis but growing evidences implicate caspases also in nonapoptotic functions. Several of these enzymes, activated in molecular platforms referred to as inflammasomes, play a role in innate immune response by processing some of the cytokines involved in inflammatory response. Caspases are requested for terminal differentiation of specific cell types, whether this differentiation process leads to enucleation or not. These enzymes play also a role in T and B lymphocyte proliferation and, in some circumstances, appear to be cytoprotective rather than cytotoxic. These pleiotropic functions implicate caspases in the control of life and death but the fine regulation of their dual effect remains poorly understood. The nonapoptotic functions of caspases implicate that cells can restrict the proteolytic activity of these enzymes to selected substrates. Deregulation of the pathways in which caspases exert these nonapoptotic functions is suspected to play a role in the pathophysiology of several human diseases.

Animals↗

PubMed2005

Rescue of early-stage myelodysplastic syndrome-deriving erythroid precursors by the ectopic expression of a dominant-negative form of FADD.

Myelodysplastic syndromes (MDSs) are characterized by peripheral blood cytopenia including anemia. We have investigated the implication of the extrinsic pathway of apoptosis in MDS-ineffective erythropoiesis by in vitro expansion of erythroid precursors from early stage (low and intermediate-1 International Prognosis Scoring System [IPSS]) MDS, advanced stage (intermediate-2 IPSS) MDS, and control bone marrow samples. We have previously shown that Fas and its ligand were overexpressed in early stage MDS erythroid cells. Here, we show that caspase-8 activity is significantly increased, whereas the expression of death receptors other than Fas, including the type 1 receptor for tumor necrosis factor alpha (TNF-alpha) and the receptors for the TNF-related apoptosis-inducing ligand (TRAIL), DR4 and DR5, was normal. We also observed that the adapter Fas-associated death domain (FADD) was overexpressed in early stage MDS erythroid cells. Transduction of early stage MDS-derived CD34+ progenitors with a FADD-encoding construct increased apoptosis of erythroid cells and dramatically reduced erythroid burst-forming unit (BFU-E) growth. Transduction of a dominant-negative (dn) mutant of FADD inhibited caspase-8 activity and cell death and rescued BFU-E growth without abrogating erythroid differentiation. These results extend the observation that Fas-dependent activation of caspase-8 accounts for apoptosis of early stage MDS erythroid cells and demonstrate for the first time that FADD is a valuable target to correct ineffective erythropoiesis in these syndromes.

Adaptor Proteins, Signal Transducing↗