Interconnections of CLN3, Hook1 and Rab proteins link Batten disease to defects in the endocytic pathway

Abstract

The endosomal/lysosomal transmembrane protein CLN3 is mutated in the Batten disease (juvenile neuronal ceroid lipofuscinosis, JNCL). However, the molecular mechanism of JNCL pathogenesis and the exact function of the CLN3 protein have remained unclear. Previous studies have shown that deletion of BTN1, the yeast orthologue of CLN3, leads to increased expression of BTN2. BTN2 encodes Btn2p, a proposed homologue to a novel microtubule-binding protein Hook1, which regulates endocytosis in Drosophila. We analysed here the putative interconnection between CLN3 and Hook1 in the mammalian cells and discovered that overexpression of human CLN3 induces aggregation of Hook1 protein, potentially by mediating its dissociation from the microtubules. Using in vitro binding assay we were able to demonstrate a weak interaction between Hook1 and the cytoplasmic segments of CLN3. We also found receptor-mediated endocytosis to be defective in CLN3-deficient JNCL fibroblasts, connecting CLN3, Hook1 and endocytosis in the mammalian system. Moreover, co-immunoprecipitation experiments showed that Hook1 physically interacts with endocytic Rab7, Rab9 and Rab11, hence delineating a manifold role for mammalian Hook1 in membrane trafficking events. These novel interactions between the microtubule-binding Hook1 and the large family of Rab GTPases also suggest a link between CLN3 function, microtubule cytoskeleton and endocytic membrane trafficking.

A Knock-In Reporter Model of Batten Disease

“…A recent report indicates that, similar to yeast cells, arginine transport into lysosomes is defective in JNCL patient-derived lymphoblasts (Ramirez-Montealegre and . Other studies with human fibroblasts indicate CLN3 involvement in lysosomal pH maintenance and degradation (Golabek et al, 2000) and endocytosis (Luiro et al, 2004). Cells derived from Cln3 ⌬ex7/8 mice display defects in endosome-to-lysosome vesicular trafficking and mitochondrial function (Fossale et al, 2004), and microarray analysis of neurons from Cln3 ⌬ex7/8 mice reveals altered levels of transcripts coding for proteins involved in synaptic, cytoskeletal, and metabolic functions (Luiro et al, 2006).…”

Alterations in striatal dopamine catabolism precede loss of substantia nigra neurons in a mouse model of juvenile neuronal ceroid lipofuscinosis

“…The function of CLN3 protein remains unknown, however, recent studies have suggested a role for CLN3 in cellular transport (Fossale et al, 2004;Luiro et al, 2004;Weimer et al, 2005). Therefore, loss of CLN3 may affect not only the intracellular transport of various cargos, but the communication between neuronal populations.…”

RIM-BP3 is a manchette-associated protein essential for spermiogenesis

“…Further circumstantial evidence comes from the fact that both RIM-BP1 and RIM-BP2, the two highly conserved parologs that are expressed in the brain, are involved in vesicle transport in neuronal cells (Hibino et al, 2002). Finally, both RIM-BP3 interacting partners Hook1 and KIF3B have been connected with Rab proteins involved in endocytosis (Imamura et al, 2003;Luiro et al, 2004). All these proteins, including RIM-BP3, Hook1, Kinesins, RIMs and Rabs, seem to be networked for complex intracellular trafficking and transport.…”