Research Article: Inhibition of Glioma Cell Lysosome Exocytosis Inhibits Glioma Invasion

Date Published: September 28, 2012

Publisher: Public Library of Science

Author(s): Yu Liu, Yijiang Zhou, Keqing Zhu, Guillermo Velasco.


Cancer cells invade by secreting enzymes that degrade the extracellular matrix and these are sequestered in lysosomal vesicles. In this study, the effects of the selective lysosome lysing drug GPN and the lysosome exocytosis inhibitor vacuolin-1 on lysosome exocytosis were studied to determine their effect on glioma cell migration and invasion. Both GPN and vacuolin-1 evidently inhibited migration and invasion in transwell experiments and scratch experiments. There are more lysosomes located on the cell membrane of glioma cells than of astrocytes. GPN decreased the lysosome number on the cell membrane. We found that rab27A was expressed in glioma cells, and colocalized with cathepsin D in lysosome. RNAi-Rab27A inhibited lysosome cathepsin D exocytosis and glioma cell invasion in an in vitro assay. Inhibition of cathepsin D inhibited glioma cell migration. The data suggest that the inhibition of lysosome exocytosis from glioma cells plays an important modulatory role in their migration and invasion.

Partial Text

The activation and release of proteases from cancer cells induces invasive, migratory behavior in vitro and metastasis in vivo [1]. Because these proteases are sequestered in lysosomes, lysosomes may be key mediators of protease release in cancer cell invasion [2]. Lysosomes play a pivotal role in the degradation of extracellular matrix (ECM) proteins, cell invasion, and cell migration into the ECM because several of the proteases that contribute to ECM degradation are directly or indirectly associated with lysosome exocytosis [3], [4]. The lysosomal cathepsins are a major class of matrix-degrading enzymes involved in tumor invasion. For instance, cathepsin D, which is sequestered in lysosomes, exhibits proteolytic activity when activated by the acidic lysosomal environment. Clinically, the level, activity and localization of cathepsins is of diagnostic and prognostic value. For example, Cathepsin D is a potential serum marker for poor prognosis in glioma patients [5], [6]. Inhibition of the exocytosis of proteases from cancer cell lysosomes could lead to the development of an efficacious therapy for cancer.

Lysosomes participate in the regulation and function of matrix metalloproteinases, serine proteases, and cathepsins, which are sequestered in lysosomal vesicles [10]. A recent study demonstrated that lysosomes are responsible for exocytosis in nonsecretory cells, such as astrocytes [12]. We found more lysosomes on the glioma cell surface than in astrocytes. We hypothesized that inhibiting lysosome exocytosis would reduce cathepsin D release and lead to reduced cancer invasion [13], [14]. Our results from the scratch motility assay indicated that GPN or vacuolin-1 modulated glioma cell movement in the two-dimensional plane. In the brain, such movement is not likely. Instead, glioma cells must be able to migrate and invade through the three-dimensional spatial constraints of the surrounding brain tissue. To replicate this type of environment more closely, we used a transwell migration assay and found that either GPN or vacuolin-1 inhibited glioma cell invasion in this three-dimensional model.