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Role of two sequence motifs of mesencephalic astrocyte-derived neurotrophic factor in its survival-promoting activity
K Mätlik1, Li-ying Yu1, A Eesmaa1
1Program in Developmental Biology, Institute of Biotechnology, University of Helsinki, Viikki Biocenter, PO Box 65, Helsinki 00014, Finland.
Abstract:
Mesencephalic astrocyte-derived neurotrophic factor (MANF) is a prosurvival protein that protects the cells when applied intracellularly in vitro or extracellularly in vivo. Its protective mechanisms are poorly known. Here we studied the role of two short sequence motifs within the carboxy-(C) terminal domain of MANF in its neuroprotective activity: the CKGC sequence (a CXXC motif) that could be involved in redox reactions, and the C-terminal RTDL sequence, an endoplasmic reticulum (ER) retention signal. We mutated these motifs and analyzed the antiapoptotic effect and intracellular localization of these mutants of MANF when overexpressed in cultured sympathetic or sensory neurons. As an in vivo model for studying the effect of these mutants after their extracellular application, we used the rat model of cerebral ischemia. Even though we found no evidence for oxidoreductase activity of MANF, the mutation of CXXC motif completely abolished its protective effect, showing that this motif is crucial for both MANF's intracellular and extracellular activity. The RTDL motif was not needed for the neuroprotective activity of MANF after its extracellular application in the stroke model in vivo. However, in vitro the deletion of RTDL motif inactivated MANF in the sympathetic neurons where the mutant protein localized to Golgi, but not in the sensory neurons where the mutant localized to the ER, showing that intracellular MANF protects these peripheral neurons in vitro only when localized to the ER.
Insights
Mesencephalic astrocyte-derived neurotrophic factor (MANF) protects cells via its CXXC motif, crucial for both intracellular and extracellular neuroprotection. The RTDL motif is essential for in vitro protection in sensory neurons by ensuring ER localization.
Area of Science:
- Neuroscience
- Cell Biology
- Molecular Biology
Background:
- Mesencephalic astrocyte-derived neurotrophic factor (MANF) is a secreted protein with known prosurvival functions.
- The precise mechanisms underlying MANF's neuroprotective activity remain largely unelucidated.
- Specific sequence motifs within MANF's C-terminal domain may play critical roles in its function.
Purpose of the Study:
- To investigate the role of two C-terminal sequence motifs, CKGC (CXXC) and RTDL, in MANF's neuroprotective activity.
- To determine the importance of these motifs for both intracellular and extracellular MANF functions.
- To analyze the impact of mutations in these motifs on MANF localization and antiapoptotic effects in neuronal cells.
Main Methods:
- Site-directed mutagenesis was used to create MANF mutants lacking the CKGC or RTDL motifs.
- Overexpression of wild-type and mutant MANF in cultured sympathetic and sensory neurons to assess antiapoptotic effects and subcellular localization.
- In vivo studies using a rat model of cerebral ischemia to evaluate the neuroprotective efficacy of extracellularly applied MANF mutants.
Main Results:
- Mutation of the CXXC motif abolished MANF's neuroprotective effect in both in vitro and in vivo models, indicating its critical importance.
- MANF did not exhibit detectable oxidoreductase activity.
- The RTDL motif was dispensable for in vivo neuroprotection after extracellular application.
- In vitro, deletion of RTDL inactivated MANF in sympathetic neurons (mutant localized to Golgi) but not in sensory neurons (mutant localized to ER).
Conclusions:
- The CXXC motif is essential for MANF's neuroprotective activity, regardless of its intracellular or extracellular application.
- MANF's neuroprotection in sensory neurons in vitro is dependent on its correct localization to the endoplasmic reticulum via the RTDL motif.
- The RTDL motif is not required for MANF's extracellular neuroprotective effects in the context of cerebral ischemia.
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