The Enlarged Lysosomes in beige_j Cells Result From Decreased Lysosome Fission and Not Increased Lysosome Fusion

Abstract

Chediak-Higashi Syndrome is an autosomal recessive disorder that affects vesicle morphology. The Chs1/Lyst protein is a member of the BEACH family of proteins. The absence of Chs1/Lyst gives rise to enlarged lysosomes. Lysosome size is regulated by a balance between vesicle fusion and fission and can be reversibly altered by acidifying the cytoplasm using Acetate Ringer’s or by incubating with the drug vacuolin-1. We took advantage of these procedures to determine rates of lysosome fusion and fission in the presence or absence of Chs1/Lyst. Here we show by microscopy, flow cytometry and in vitro fusion that the absence of the Chs1/Lyst protein does not increase the rate of lysosome fusion. Rather, our data indicate that loss of this protein decreases the rate of lysosome fission. We further show that overexpression of the Chs1/Lyst protein gives rise to a faster rate of lysosome fission. These results indicate that Chs1/Lyst regulates lysosome size by affecting fission.

Comparison of Dictyostelium LvsB and endosomal fission defect mutants support a fusion regulatory role for LvsB

“…Adding to the possible complexity of Lyst function are the findings of Durchfort (Durchfort et al, 2012). Although our comparative analyses have shown strong evidence that the LvsB mutant phenotype arises from inappropriate fusion, they presented strong evidence that the mouse Lyst homolog promotes fission from drug-induced enlarged endosomal compartments.…”

“…The fission model for Lyst and LvsB function predicts that the delayed maturation of lysosomes should cause an increase in vesicle size at the stage where maturation is delayed (Durchfort et al, 2012). Delaying the maturation of lysosomes is predicted to allow the continued flow of endosomes that are competent to undergo homotypic fusion.…”

“…An alternative model suggested that Lyst functions to control lysosomal fission instead of fusion (Burkhardt et al, 1993). Studies in mice (Perou et al, 1997;Durchfort et al, 2012) and Dictyostelium (Charette and Cosson, 2007;Charette and Cosson, 2008) have attributed beige and LvsB mutant defects, respectively, to decreased lysosomal fission. Despite decades of research across a plethora of model systems, a unifying model for Lyst function has not been established.…”

The cytotoxic T lymphocyte immune synapse at a glance

“…Mutations in the LYST protein that give rise to CHS have been suggested to cause a fission defect that entails the formation of enlarged lysosomes, whose excessive size appears to prevent fusion at the immune synapse (Baetz et al, 1995;Durchfort et al, 2012). A recent report shows that overexpression of either Rab27a alone or Rab27a together with Slp3 (also known as SYTL3) partially restores granule secretion [measured by appearance of the lysosomal membrane protein CD107a (also known as LAMP1) at the cell surface] and that coexpression of Rab27a, Munc13-4 and Slp3 rescues the secretion defect of CHS CTLs.…”

Characterization of Mast Cell Secretory Granules and Their Cell Biology

“…Mutations that perturb this process, for example, mutations in the Chediak-Higashi syndrome/ lysosomal trafficking regulator (CHS/Lyst) in humans, with the Chediak-Higashi syndrome, and in beige (Lyst bg /Lyst bg ) mice (Durchfort et al, 2012) result in giant SGs and can cause significant pathology. Indeed, we have shown that the same phenotype of increased sized SGs is caused by knockdown of synaptotagmin 3, a member of the synaptotagmin family of traffic regulating proteins (Grimberg et al, 2003) that regulates endocytic recycling (Grimberg et al,…”