GOLPH3 depletion in glioblastoma cells promotes anti-tumor effects and neuronal differentiation by affecting mTOR signaling.

Glioblastoma is the most aggressive primary brain tumor in adults. Resistance of glioblastoma to the standard chemotherapy agent temozolomide (TMZ) correlates with the expression of the DNA repair enzyme O6-Methylguanine-DNA methyltransferase (MGMT). Additionally, tumor initiation and recurrence are associated with a subpopulation of glioblastoma stem cells (GSCs) which exhibit self-renewal properties, multipotency, and resistance to both chemotherapy and radiotherapy. To identify novel molecular biomarkers and therapeutic targets, we investigated the possible role of the oncoprotein Golgi phosphoprotein 3 (GOLPH3) in glioblastoma. GOLPH3 is overexpressed in many solid tumors and confers resistance to DNA-damaging chemotherapeutic agents. Its overexpression is also associated with poor prognosis in a variety of cancers, including glioblastoma. Here, we show that GOLPH3 knockdown in U87MG glioblastoma cells inhibits cell proliferation, promotes senescence and induces striking cellular and molecular changes toward a neuron-like phenotype. We analyzed the constitutive expression of GOLPH3, MGMT and mechanistic target of rapamycin (mTOR) signaling proteins in U87MG cells and in three GSCs representative of the three glioblastoma molecular subtypes. Our results suggest that these glioblastoma cell models may exhibit distinct responses to mTOR inhibition and TMZ. Finally, we show that GOLPH3 depletion reduces the activity of both mTOR complex 1 and 2 leading to decreased phosphorylation of their respective downstream targets S6K and Akt in both U87MG cells and the BT379 GSCs subtype. Our findings identify a potential therapeutic vulnerability that can be exploited to develop patient-tailored treatments in glioblastoma.