red Purkinje cells , leading to impairment of UPS and apoptotic cell death, as in other 15182727” neurodegenerative diseases. We have also shown that mutant cPKC induces improper development of PC dendrites in an aggregate-independent manner. Furthermore, mutant cPKC has aberrant kinase activities, higher basal activity in the cytosol and lower activity at the plasma membrane when activated. These findings suggest that mechanisms other than aggregation could participate in the neurodegeneration of cerebellar Purkinje cells in SCA14. To clarify the aggregateindependent mechanism, we used our newly established method for monitoring CMA to investigate whether mutant cPKC affects CMA activity in primary cultured PCs. Results Single-cell monitoring of CMA activity by visualizing lysosomal accumulation of a CMA substrate using the HaloTag system In the process of CMA, cytosolic substrate proteins for CMA are recognized by heat shock cognate protein 70, a molecular chaperone. The substrates are then transferred to the lysosome, where they are translocated through lysosome-associated membrane protein type 2A and subsequently degraded by lysosomal proteases. Translocation of CMA substrates from the cytosol to lysosomes is a crucial step in CMA and thus indicates CMA activity. To monitor CMA 
activity at the single-cell level, we visualized the translocation of a CMA substrate from the cytosol to lysosomes using the HaloTag system. HT-fused proteins produced in cells can be labeled by brief extracellular application of a fluorescently labeled HT ligand. When HT-fused proteins are exposed to an HT ligand, the HT covalently binds the HT ligand at neutral pH but does not bind in the acidic lysosome, suggesting that only extralysosomal proteins are labeled by a fluorescent HT ligand. R115777 However, when ” HT-fused proteins are fluorescently labeled in the cytosol and translocated to lysosomes after further cultivation, the fluorescent labels and Oregon green ) continue to fluoresce. Using this property, we sought to monitor the translocation of GAPDH, a well-known CMA substrate, from the cytosol to lysosomes. GAPDH fused to HT was expressed in HeLa cells using adenoviral vectors, and cells were incubated 10 min with a TMR-labeled HT ligand. Immediately after labeling, TMR-labeled GAPDH-HT was uniformly distributed in the cytoplasm, but 21 h of additional incubation led to dot-like cytoplasmic accumulations of GAPDHHT in several cells. Immediately after labeling, GAPDHHT did not colocalize with immunostained LAMP2, a lysosomal marker protein, suggesting that only extralysosomal GAPDH-HT was labeled with the TMR-HT ligand. In contrast, the dot-like accumulations of GAPDH-HT after further incubation strongly colocalized with LAMP2. Furthermore, these dot-like accumulations of GAPDH-HT, labeled with OG-HT ligand, strongly colocalized with LysoTracker-red, a fluorescent lysosomal marker. These results indicate that translocation of GAPDH-HT to lysosomes can be visualized using the HT system. Next, we examined whether this translocation is mediated by CMA. Mammalian LAMP2, which is localized in the lysosomal membrane, consists of three splicing isoforms that are alternatively spliced in their carboxyl termini. Among the isoforms, only LAMP2A is involved in CMA as a lysosomal receptor for CMA substrates. Most dots of GAPDH-HT were colocalized with LAMP2A-specific antibody staining, indicating that GAPDH-HT accumulates in lysosomes containing LAMP2A. Next, we examined whether