title: Dileucine and PDZ-binding motifs mediate synaptic adhesion-like molecule 1 (SALM1) trafficking in hippocampal neurons.
abstract: Synaptic adhesion-like molecules (SALMs) are a family of cell adhesion molecules involved in neurite outgrowth and synapse formation. Of the five family members, only SALM1, -2, and -3 contain a cytoplasmic C-terminal PDZ-binding motif. We have found that SALM1 is unique among the SALMs because deletion of its PDZ-binding motif (SALM1ΔPDZ) blocks its surface expression in heterologous cells. When expressed in hippocampal neurons, SALM1ΔPDZ had decreased surface expression in dendrites and the cell soma but not in axons, suggesting that the PDZ-binding domain may influence cellular trafficking of SALMs to specific neuronal locations. Endoglycosidase H digestion assays indicated that SALM1ΔPDZ is retained in the endoplasmic reticulum (ER) in heterologous cells. However, when the entire C-terminal tail of SALM1 was deleted, SALM1 was detected on the cell surface. Using serial deletions, we identified a region of SALM1 that contains a putative dileucine ER retention motif, which is not present in the other SALMs. Mutation of this DXXXLL motif allowed SALM1 to leave the ER and enhanced its surface expression in heterologous cells and neurons. An increase in the number of protrusions at the dendrites and cell body was observed when this SALM1 mutant was expressed in hippocampal neurons. With electron microscopy, these protrusions appeared to be irregular, enlarged spines and filopodia. Thus, enrichment of SALM1 on the cell surface affects dendritic arborization, and intracellular motifs regulate its dendritic versus axonal localization.
authors.affiliation: Laboratory of Neurochemistry, NIDCD/National Institutes of Health, 50 South Dr., Bldg. 50, Rm. 4144, Bethesda, MD20892-8027, USA. Gail.Seabold@nih.gov
authors.forename: Gail K
authors.initials: GK
authors.lastname: Seabold
authors.forename: Philip Y
authors.initials: PY
authors.lastname: Wang
authors.forename: Ronald S
authors.initials: RS
authors.lastname: Petralia
authors.forename: Kai
authors.initials: K
authors.lastname: Chang
authors.forename: Arthur
authors.initials: A
authors.lastname: Zhou
authors.forename: Mark I
authors.initials: MI
authors.lastname: McDermott
authors.forename: Ya-Xian
authors.initials: YX
authors.lastname: Wang
authors.forename: Sharon L
authors.initials: SL
authors.lastname: Milgram
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Wenthold
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001369:Axons / Q000378:metabolism* / Q000648:ultrastructure; D015816:Cell Adhesion Molecules, Neuronal / Q000235:genetics / Q000378:metabolism*; D003712:Dendrites / Q000378:metabolism* / Q000648:ultrastructure; D006367:HeLa Cells; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D054731:PDZ Domains; D021381:Protein Transport / Q000502:physiology; D017384:Sequence Deletion
chemical_list: D015816:Cell Adhesion Molecules, Neuronal; D009419:Nerve Tissue Proteins