dictyNews

Electronic Edition

Volume 49, number 29

November 22, 2023



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Abstracts

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Mechanisms regulating the intracellular trafficking and release of 

CLN5 and CTSD



Robert J. Huber1,2,*, William D. Kim2, and Morgan L.D.M. 

Wilson-Smillie2 



1Department of Biology, Trent University, Peterborough, Ontario, 

Canada

2Environmental and Life Sciences Graduate Program, Trent 

University, Peterborough, Ontario, Canada

*Corresponding author





Traffic, accepted



Ceroid lipofuscinosis neuronal 5 (CLN5) and cathepsin D (CTSD) 

are soluble lysosomal enzymes that also localize extracellularly. 

In humans, homozygous mutations in CLN5 and CTSD cause 

CLN5 and CLN10 disease, respectively, which are two subtypes 

of neuronal ceroid lipofuscinosis (NCL, commonly known as Batten 

disease). The mechanisms regulating the intracellular trafficking of 

CLN5 and CTSD and their release from cells are not well understood. 

Here, we used the social amoeba Dictyostelium discoideum as a 

model system to examine the pathways and cellular components 

that regulate the intracellular trafficking and release of the 

D. discoideum homologs of human CLN5 (Cln5) and CTSD (CtsD). 

We show that both Cln5 and CtsD contain signal peptides for 

secretion that facilitate their release from cells. Like Cln5, 

extracellular CtsD is glycosylated. In addition, Cln5 release is 

regulated by the amount of extracellular CtsD. Autophagy induction 

promotes the release of Cln5, and to a lesser extent, CtsD. Release 

of Cln5 requires the autophagy proteins, Atg1, Atg5, and Atg9, as 

well as autophagosomal-lysosomal fusion. Atg1 and Atg5 are 

required for the release of CtsD. Together, these data support a 

model where Cln5 and CtsD are actively released from cells via 

their signal peptides for secretion and pathways linked to autophagy. 

The release of Cln5 and CtsD from cells also requires 

microfilaments and the D. discoideum homologs of human AP-3 

complex mu subunit, the lysosomal-trafficking regulator LYST, 

mucolipin-1, and the Wiskott–Aldrich syndrome-associated protein 

WASH, which all regulate lysosomal exocytosis in this model 

organism. These findings suggest that lysosomal exocytosis also 

facilitates the release of Cln5 and CtsD from cells. In addition, we 

report the roles of ABC transporters, microtubules, osmotic stress, 

and the putative D. discoideum homologs of human sortilin and 

cation-independent mannose-6-phosphate receptor in regulating 

the intracellular/extracellular distribution of Cln5 and CtsD. In total, 

this study identifies the cellular mechanisms regulating the release 

of Cln5 and CtsD from D. discoideum cells and provides insight 

into how altered trafficking of CLN5 and CTSD causes disease 

in humans.





Submitted by Robert Huber [[log in to unmask]]

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[End dictyNews, volume 49, number 29]