038 | Endocytic trafficking of Gpm6a is altered by mutation of the key residue E258 critical for its function in filopodia formation

Cellular and Molecular Neurobiology

Author: Maria Belén Montiel | Email: mariabelenmontiel@gmail.com

Maria Belén Montiel , Nicolás Matias Rosas , Beata Fuchsova

1° Instituto de Investigaciones Biotecnológicas, Escuela de Bio y Nanotecnologías (EByN), Universidad Nacional de San Martín (UNSAM) – Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), San Martín, Buenos Aires, Argentina

Gpm6a is a neuronal membrane glycoprotein that functions in the processes of neuronal
development and its overexpression leads to the extensive formation of filopodia. Previously,
we showed that Gpm6a lacking C- but not N-terminal cytoplasmic tail fails to induce
filopodium formation and we identified K250, K255, and E258 within the C-terminus as the key
functional residues in this process. We observed that Gpm6a lacking C-terminus and the point
mutation E258A, display high accumulation in the cytosol suggesting that cell surface
trafficking is affected. Since different types of membrane outgrowth, filopodia formation
including, require polarized membrane transport we hypothesized that the incapacity of the
mutant Gpm6a to induce filopodium formation could be linked to the disrupted trafficking of
mutant Gpm6a.
Here, we show using confocal microscopy that the mutant forms of Gpm6a that fail to
induce filopodia formation display preferential localization to the Lamp1-positive structures.
Our colocalization assays show that the wt Gpm6a and all studied mutant proteins clearly
progress from the plasma membrane to Lamp1-containing late endosomal/ lysosomal structures
but the Gpm6a ?C-EGFP and E258-EGFP mutations result in increased accumulation of
Gpm6a in these compartments. At the same time, the overexpression of E258-EGFP leads to
decreased neuronal arborization as assessed by Sholl analysis and differences in the
colocalization of Gpm6a with Rab 11.