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Clinical mutations in the L1 neural cell adhesion molecule affect cell-surface expression
H D Moulding1, R L Martuza, S D Rabkin
1Interdisciplinary Program for Neuroscience and Department of Neurosurgery, Georgetown University Medical Center, Washington, DC 20007, USA.
Summary
Missense mutations in L1 cell adhesion molecule (L1CAM) can impair protein trafficking, leading to neurological disorders. Some L1CAM mutations prevent proper cell surface expression and processing, causing disease similar to complete L1CAM loss.
Area of Science:
- Neuroscience
- Molecular Biology
- Genetics
Background:
- Mutations in the L1 neural cell adhesion molecule (L1CAM) are linked to congenital neurological syndromes.
- These mutations, often single amino acid changes, affect various protein domains.
Purpose of the Study:
- To investigate the impact of specific L1CAM missense mutations on protein expression, trafficking, and function.
- To determine if impaired protein trafficking can explain the severity of L1CAM-associated neurological disorders.
Main Methods:
- Utilized defective herpes simplex virus vectors to express wild-type and mutant L1CAM proteins (R184Q, D598N, S1194L).
- Assessed neurite outgrowth of cerebellar granule cells on astrocytes expressing different L1CAM variants.
- Employed live cell immunofluorescent staining and endoglycosidase H (endoH) sensitivity assays to evaluate protein expression and processing.
Main Results:
- Mutant L1CAM proteins R184Q and D598N significantly reduced neurite outgrowth compared to wild-type or S1194L.
- R184Q and D598N L1CAM showed drastically diminished cell-surface expression across various cell types.
- These mutants exhibited altered molecular weights and remained endoH-sensitive, indicating incomplete post-translational modification.
Conclusions:
- Certain L1CAM missense mutations disrupt protein trafficking, leading to reduced cell-surface expression.
- Impaired trafficking and processing of L1CAM can cause neurological phenotypes independent of direct functional impairment.
- This mechanism provides a rationale for severe clinical outcomes resulting from single amino acid changes in L1CAM.