CLN7 is a polytopic lysosomal membrane protein deficient in variant late infantile neuronal ceroid lipofuscinosis, a neurodegenerative lysosomal storage disorder. In this study fluorescence protease protection assays and mutational analyses revealed the N-and C-terminal tails of CLN7 in the cytosol and two N-glycosylation sites at N371 and N376. Both partially and non-glycosylated CLN7 were correctly transported to lysosomes. To identify lysosomal targeting motifs, we generated CD4-chimera fused to the N-and C-terminal domains of CLN7. Lysosomal localization of the chimeric proteins requires a consensus acidic dileucine-based motif in the N-terminus and two tandem tyrosine-based signals in the C-terminus. Mutation of these sorting motifs resulted in cell surface redistribution of CD4 chimeras. However, the dileucine-based motif is of critical importance for lysosomal localization of the full-length CLN7 in different cell lines. Cell surface biotinylation revealed that at equilibrium 22% of total CLN7 is localized at the plasma membrane. Mutation of the dileucine motif or the co-expression of dominantnegative mutant dynamin K44A led to a further increase of CLN7 at the plasma membrane. Our data demonstrate that CLN7 contains several cytoplasmic lysosomal targeting signals of which the N-terminal dileucine-based motif is required for the predominant lysosomal targeting along the indirect pathway and clathrin-mediated endocytosis of CLN7.
The ganglioglioma, a mixed tumor with neuronal and glial elements, occurs occasionally in children and young adults. Its incidence, clinical presentation, radiological features, and natural history have not been clearly defined. A review of 111 primary brain tumors treated at our institution shows that 9.0% were gangliogliomas. The temporal lobe was the most common site involved. All patients presented with seizures but were neurologically intact. The CT scan showed a partially calcified mass, frequently isodense or nearly so, with minimal enhancement. Complete removal produced dramatic improvement in seizure control. Radiotherapy and/or chemotherapy are reserved for tumors showing malignant changes in the astrocytic component. Patients with chronic epilepsy, or whose seizures escape control despite anticonvulsants, should be examined with this tumor in mind. Following removal of these low-grade temporal lobe tumors, fewer seizures are seen, and the long-term prognosis is very good.
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