The role of HDAC10 in lysosomal stress-response mechanisms

Neuroblastoma is the most common solid extracranial childhood malignancy and the response of high-risk patients to chemotherapy is poor, underlining the need for novel treatment regimens. Previous data from our lab indicate that histone deacetylase 10 (HDAC10) is important for the homeostasis of lysosomes, i.e. acidic vesicular organelles that are involved in the degradation of various biomolecules. These organelles are of central importance in cellular stress resistance mechanisms such as macroautophagy, a starvation-induced degradation process that allows for the recycling of cellular components such as aged or redundant organelles and protein aggregates. Indeed, it was shown that inhibition of HDAC10 sensitizes neuroblastoma as well as medulloblastoma cells to chemotherapeutic agents, making HDAC10 a promising and druggable target for treatment of therapy-resistant tumor entities.

In this project, we aim to unravel the role of HDAC10 in lysosomal biology and stress resistance using cell culture-based flow cytometric and immunofluorescence methods with a particular focus on lysosomal exocytosis. In this process, lysosomes fuse with the plasma membrane in order to release their content to the extracellular space, and tumor cells can use this mechanism to get rid of chemotherapeutic agents.

Here, we show that both depletion and inhibition of HDAC10 increase intracellular presence of chemotherapeutic agents, such as doxorubicin, in neuroblastoma cells. Intracellular amounts of doxorubicin were further enhanced by addition of lysosomal inhibitors, such as chloroquine (CQ). RNAi-mediated depletion of HDAC10 leads to a reduced presence of the lysosomal marker LAMP1 at the cell surface, indicating that HDAC10 depletion decreases lysosomal exocytosis. This is further supported by kinetic experiments demonstrating that HDAC10 inhibition decreases secretion of chemotherapeutic drugs.

Our data imply that interference with HDAC10 promotes the uptake of chemotherapeutics into tumor cells while decreasing lysosomal exocytosis.