P02.08.b role of the protein network of the paracaspase malt1 in self-renewal properties of glioblastoma cells

Abstract BACKGROUND Glioblastoma is the most common and most aggressive brain tumor in adults. Despite standard treatment combining surgery, radiotherapy and chemotherapy, relapse is inevitable, making this cancer a major public health issue. Within this tumor reside cells with a stem-like character, called GSCs for Glioblastoma Stem-like Cells, which maintain, initiate, and propagate the tumor, making them a potential target to hinder glioblastoma. These cells constitute a reservoir of heterogeneous cells capable of differentiating into neural lineage cell types. In this context, lysosomal homeostasis plays a key role in the maintenance of the GSC reservoir. Furthermore, previous studies demonstrated that the paracaspase MALT1 is a major regulator of lysosomal homeostasis: MALT1 is required for GSC viability as well as for the maintenance of stemness by modulating the abundance of lysosomal proteins. This current study addresses the issue of the balance between self-renewal and viability of GSCs. In addition, this project aims to identify and characterize an actor of self-renewal mechanisms that does not impact the survival-death balance of primary cells from patients. MATERIAL AND METHODS An initial analysis combining DepMap and String Network databases allowed us to select potential relays of the MALT1 activity in GSCs. A functional screening was then set up and performed in GSCs derived from patients to identify among 20 candidates those regulating cell expansion without impacting viability. RESULTS The strategy of functional screening allowed the selection of 14 genes with a global viability effect, while only 2 genes were affecting self-renewal while sparing viability in vitro. We next pursued with one of the identified targets, from the IKK family. The involvement of this serine/threonine protein kinase was then confirmed in multiple patient cells and in CRISPR-mediated knock-out. Future experiments will decipher the involvement of this kinase in the self-renewal properties of GSCs. CONCLUSION This study highlights a putative candidate specifically operating on the self-renewal of glioblastoma cells, that does not affect the life-death balance. Future investigations will permit to characterize and understand the underlying mechanisms.