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Biomedical subjects

Patrick Mehlen

Publications and source records attributed to Patrick Mehlen.

26 records · Page 2Linked to original sources
PubMed2003

GDNF-deprived sympathetic neurons die via a novel nonmitochondrial pathway.

The mitochondrial death pathway is triggered in cultured sympathetic neurons by deprivation of nerve growth factor (NGF), but the death mechanisms activated by deprivation of other neurotrophic factors are poorly studied. We compared sympathetic neurons deprived of NGF to those deprived of glial cell line-derived neurotrophic factor (GDNF). In contrast to NGF-deprived neurons, GDNF-deprived neurons did not die via the mitochondrial pathway. Indeed, cytochrome c was not released to the cytosol; Bax and caspase-9 and -3 were not involved; overexpressed Bcl-xL did not block the death; and the mitochondrial ultrastructure was not changed. Similarly to NGF-deprived neurons, the death induced by GDNF removal is associated with increased autophagy and requires multiple lineage kinases, c-Jun and caspase-2 and -7. Serine 73 of c-Jun was phosphorylated in both NGF- and GDNF-deprived neurons, whereas serine 63 was phosphorylated only in NGF-deprived neurons. In many NGF-deprived neurons, the ultrastructure of the mitochondria was changed. Thus, a novel nonmitochondrial caspase-dependent death pathway is activated in GDNF-deprived sympathetic neurons.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Inhibition of neuroepithelial patched-induced apoptosis by sonic hedgehog.

During early development in vertebrates, Sonic hedgehog (Shh) is produced by the notochord and the floor plate. A ventrodorsal gradient of Shh directs ventrodorsal patterning of the neural tube. However, Shh is also required for the survival of neuroepithelial cells. We show that Patched (Ptc) induces apoptotic cell death unless its ligand Shh is present to block the signal. Moreover, the blockade of Ptc-induced cell death partly rescues the chick spinal cord defect provoked by Shh deprivation. Thus, the proapoptotic activity of unbound Ptc and the positive effect of Shh-bound Ptc on cell differentiation probably cooperate to achieve the appropriate spinal cord development.

Animals↗
PubMed2003

The netrin-1 receptors UNC5H are putative tumor suppressors controlling cell death commitment.

The three mammalian receptors UNC5H1, UNC5H2, and UNC5H3 (also named UNC5A, UNC5B, and UNC5C in human) that belong to the family of the netrin-1 receptors, UNC5H, were initially proposed as mediators of the chemorepulsive effect of netrin-1 on specific axons. However, they were also recently shown to act as dependence receptors. Such receptors induce apoptosis when unbound to their ligand. We show here that the expression of the human UNC5A, UNC5B, or UNC5C is down-regulated in multiple cancers including colorectal, breast, ovary, uterus, stomach, lung, or kidney cancers. In colorectal tumors, this down-regulation is associated with loss of heterozygosity occurring within UNC5A, UNC5B, and UNC5C genes but may also be partially related to epigenetic processes because histone deacetylase inhibitor increased UNC5C expression in various cancer cell lines. Moreover, sequencing of UNC5C gene in patients with colorectal tumors revealed the presence of missense mutations. The lossreduction of expression may be a crucial mechanism for tumorigenicity because the expression of UNC5H1, UNC5H2, or UNC5H3 inhibits tumor cell anchorage-independent growth and invasion. Moreover, these hallmarks of malignant transformation can be restored by netrin-1 addition or apoptosis inhibition. Hence, UNC5H1, UNC5H2, and UNC5H3 receptors may represent tumor suppressors that inhibit tumor extension outside the region of netrin-1 availability by inducing apoptosis.

3T3 Cells↗
PubMed2003

The dependence receptors DCC and UNC5H as a link between neuronal guidance and survival.

Netrins are secreted proteins that play a crucial role in neuronal migration and in axon guidance during the development of the nervous system. Netrin-1 has been shown to interact with the transmembrane receptors DCC and UNC5H and these receptors appeared of key importance in mediating the chemotropic activity of netrin-1. Before the discovery of DCC as a netrin-1 receptor, the gene encoding DCC was proposed as a putative tumor suppressor gene because one DCC allele was deleted in roughly 70% of colorectal cancers and its expression was often reduced or absent in colorectal cancer tissues. A putative explanation for such dual roles has recently emerged with the observation that DCC belongs to the growing family of dependence receptors. Such receptors share the property of inducing apoptosis in the absence of ligand, hence creating a cellular state of dependence on the ligand. The other netrin-1 receptors UNC5H were also subsequently proposed to be dependence receptors, suggesting that netrin-1 may not only be a chemotropic factor for neurons but also a survival factor. We describe here netrin-1 and its receptors, together with the molecular signaling pathways initiated upon netrin-1 binding or upon netrin-1 withdrawal leading respectively to axonal/neuronal guidance or cell death induction. We then conclude to the possible roles of DCC and UNC5H pro-apoptotic activities in both nervous system development and tumorigenesis.

Animals↗
PubMed2002

Caspase cleavage of the transcription factor FLI-1 during preB leukemic cell death.

Programmed cell death (apoptosis) is a complex phenomenon that is mediated in mammals mainly via the selective cleavage of intracellular proteins by the large family of cysteine aspartate protease caspases. Apoptosis is tightly regulated by the competitive effect of numerous proteins displaying either pro-apoptotic or anti-apoptotic activity. The ETS-family transcription factor FLI-1, frequently associated with malignant transformation, has been shown to display anti-apoptotic activity in several cell types including avian erythroblasts, mouse fibroblasts or lymphoid cells. We show here that apoptosis of murine preB leukemic cells is accompanied with the specific cleavage of FLI-1 by a caspase-like activity. We also demonstrate that the two isoforms of FLI-1 are indeed cleaved at three conserved sites by caspase 3 in vitro. The conservation of these cleavage sites among species suggests that the caspase cleavage of the anti-apoptotic transcription factor FLI-1 may represent a critical step to ensure irreversible cell death.

Animals↗
PubMed2002

Netrin-1-mediated axon outgrowth requires deleted in colorectal cancer-dependent MAPK activation.

Neuronal growth cones are guided to their targets by attractive and repulsive guidance cues. In mammals, netrin-1 is a bifunctional cue, attracting some axons and repelling others. Deleted in colorectal cancer (Dcc) is a receptor for netrin-1 that mediates its chemoattractive effect on commissural axons, but the signalling mechanisms that transduce this effect are poorly understood. Here we show that Dcc activates mitogen-activated protein kinase (MAPK) signalling, by means of extracellular signal-regulated kinase (ERK)-1 and -2, on netrin-1 binding in both transfected cells and commissural neurons. This activation is associated with recruitment of ERK-1/2 to a Dcc receptor complex. Inhibition of ERK-1/2 antagonizes netrin-dependent axon outgrowth and orientation. Thus, activation of MAPK signalling through Dcc contributes to netrin signalling in axon growth and guidance.

3T3 Cells↗