title: LAPTMs regulate lysosomal function and interact with mucolipin 1: new clues for understanding mucolipidosis type IV.
abstract: Loss-of-function mutations in mucolipin 1 (MCOLN1) result in mucolipidosis type IV (MLIV), a lysosomal storage disorder characterized by severe mental and psychomotor retardation. MCOLN1 is a lysosomal ion channel that belongs to the transient receptor potential (TRP) superfamily. To better understand the cellular function of MCOLN1, a split-ubiquitin yeast two-hybrid screen was performed with the purpose of revealing new MCOLN1 interaction partners. The screen identified two members of the lysosome-associated protein transmembrane (LAPTM) family as novel interaction partners of MCOLN1. The binding between MCOLN1 and LAPTM members (LAPTMs) was confirmed by co-immunoprecipitation and yeast two-hybrid assays. In addition, MCOLN1 and LAPTMs extensively colocalize at late endosomes and lysosomes. Overexpression of LAPTM4b caused enlargement of lysosomes and defective lysosomal degradation, indicating that LAPTMs are important for proper lysosomal function. Interestingly, lysosomal swelling induced by LAPTM4b was rescued by expression of MCOLN1, suggesting a functional connection between the two proteins. Finally, depletion of endogenous LAPTMs by siRNA induced accumulation of concentric multi-lamellar structures and electron-dense inclusions that closely resemble the structures found in MLIV cells. Overall, our data provide new insight into the molecular mechanisms of MCOLN1 function and suggest a potential role for LAPTMs in MLIV pathogenesis.
authors.affiliation: Laboratory of Cell Biology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Silvia
authors.initials: S
authors.lastname: Vergarajauregui
authors.forename: Jose A
authors.initials: JA
authors.lastname: Martina
authors.forename: Rosa
authors.initials: R
authors.lastname: Puertollano
mesh_terms: D011992:Endosomes / Q000378:metabolism; D004847:Epithelial Cells; D006367:HeLa Cells; D006801:Humans; D047468:Immunoprecipitation; D008247:Lysosomes / Q000378:metabolism / Q000473:pathology / Q000648:ultrastructure; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D009081:Mucolipidoses / Q000503:physiopathology*; D015513:Oncogene Proteins / Q000235:genetics / Q000502:physiology*; D011485:Protein Binding; D050053:TRPM Cation Channels / Q000235:genetics / Q000502:physiology*; D050051:Transient Receptor Potential Channels; D020798:Two-Hybrid System Techniques
chemical_list: C477083:LAPTM4B protein, human; C416674:MCOLN1 protein, human; D008565:Membrane Proteins; D015513:Oncogene Proteins; D050053:TRPM Cation Channels; D050051:Transient Receptor Potential Channels; C100848:LAPTM5 protein, human