Defective intracellular transport of CLN3 is the molecular basis of Battendisease (JNCL)

Batten disease [juvenile-onset neuronal ceroid lipofuscinosis (JNCL)], the most common progressive encephalopathy of childhood, is caused by mutations in a novel lysosomal membrane protein (CLN3) with unknown function. In thi s study, we have confirmed the lysosomal localization of the CLN3 protein b y immunoelectron microscopy by co-localizing it with soluble and membrane-a ssociated lysosomal proteins. We have analysed the intracellular processing and localization of two mutants, 461-677del; which is present in 85% of CL N3 alleles and causes the classical JNCL, and Q295K, which is a rare missen se mutation associated with an atypical form of JNCL, Pulse-chase labelling and immunoprecipitation of the two mutant proteins in COS-l-cells indicate d that 461-677del is synthesized as an similar to 24 kDa truncated polypept ide, whereas the maturation of Q295K resembles that of the wild-type CLN3 p olypeptide, Transient expression of the two mutants in BHK cells showed tha t 461-677del is retained in the endoplasmic reticulum, whereas Q295K was ca pable of reaching the lysosomal compartment, The CLN3 polypeptides were exp ressed further in mouse primary neurons where the wildtype CLN3 protein was localized both in the cell soma and in neuronal extensions, whereas the 46 1-677del mutant was arrested in the cell soma, Interestingly, co-localizati on of the wild-type CLN3 and Q295K proteins with a synaptic vesicle marker indicates that the CLN3 protein might participate in synaptic vesicle trans port/transmission. The data presented here provide clear evidence for a cel lular distinction between classical and atypical forms of Batten disease bo th in neural and non-neural cells.