Related Experiment Videos
The MLK family mediates c-Jun N-terminal kinase activation in neuronal apoptosis
Z Xu1, A C Maroney, P Dobrzanski
1Department of Pathology and Center for Neurobiology and Behavior, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA.
Abstract:
Neuronal apoptotic death induced by nerve growth factor (NGF) deprivation is reported to be in part mediated through a pathway that includes Rac1 and Cdc42, mitogen-activated protein kinase kinases 4 and 7 (MKK4 and -7), c-Jun N-terminal kinases (JNKs), and c-Jun. However, additional components of the pathway remain to be defined. We show here that members of the mixed-lineage kinase (MLK) family (including MLK1, MLK2, MLK3, and dual leucine zipper kinase [DLK]) are expressed in neuronal cells and are likely to act between Rac1/Cdc42 and MKK4 and -7 in death signaling. Overexpression of MLKs effectively induces apoptotic death of cultured neuronal PC12 cells and sympathetic neurons, while expression of dominant-negative forms of MLKs suppresses death evoked by NGF deprivation or expression of activated forms of Rac1 and Cdc42. CEP-1347 (KT7515), which blocks neuronal death caused by NGF deprivation and a variety of additional apoptotic stimuli and which selectively inhibits the activities of MLKs, effectively protects neuronal PC12 cells from death induced by overexpression of MLK family members. In addition, NGF deprivation or UV irradiation leads to an increase in both level and phosphorylation of endogenous DLK. These observations support a role for MLKs in the neuronal death mechanism. With respect to ordering the death pathway, dominant-negative forms of MKK4 and -7 and c-Jun are protective against death induced by MLK overexpression, placing MLKs upstream of these kinases. Additional findings place the MLKs upstream of mitochondrial cytochrome c release and caspase activation.
Insights
Mixed-lineage kinases (MLKs) are identified as key mediators in neuronal apoptosis signaling, acting upstream of MKK4/7 and c-Jun. Inhibition of MLKs protects neurons from death, highlighting their therapeutic potential.
Area of Science:
- Neuroscience
- Cell Biology
- Molecular Biology
Background:
- Neuronal apoptotic death pathways are complex.
- Nerve growth factor (NGF) deprivation triggers neuronal death.
- The signaling cascade involving Rac1/Cdc42, MKK4/7, JNKs, and c-Jun is partially understood.
Purpose of the Study:
- To identify novel components in the NGF deprivation-induced neuronal death pathway.
- To elucidate the role of mixed-lineage kinases (MLKs) in neuronal apoptosis.
- To determine the precise position of MLKs within the death signaling cascade.
Main Methods:
- Expression analysis of MLK family members in neuronal cells.
- Overexpression and dominant-negative studies of MLKs in PC12 cells and sympathetic neurons.
- Assessment of MLK activity using CEP-1347 (KT7515).
- Analysis of endogenous DLK levels and phosphorylation following NGF deprivation or UV irradiation.
Main Results:
- MLK family members (MLK1-3, DLK) are expressed in neurons and function between Rac1/Cdc42 and MKK4/7.
- MLK overexpression induces neuronal apoptosis, while MLK inhibition prevents it.
- CEP-1347 protects against MLK-induced death and NGF deprivation-induced death.
- Endogenous DLK levels and phosphorylation increase upon apoptotic stimuli.
- MLKs are positioned upstream of MKK4/7, c-Jun, mitochondrial cytochrome c release, and caspase activation.
Conclusions:
- MLKs play a critical role in mediating neuronal apoptotic death.
- MLKs represent a crucial signaling node upstream of key apoptotic effectors.
- Targeting MLKs offers a potential therapeutic strategy for preventing neuronal death.