CSIG-22. CAMKIIΓ INTERACTS WITH HIF-1Α IN AN OXYGEN-INDEPENDENT MANNER TO DRIVE PLASTICITY IN GLIOBLASTOMA

Abstract Glioblastoma (GBM) is a highly aggressive brain tumor that demonstrates treatment resistance. Hypoxia-inducible factor 1-alpha (HIF-1α) plays a crucial role in GBM progression and recurrence. While HIF-1α overexpression is correlated with poor GBM survival, clinical inhibitors have shown limited efficacy due to compensatory pathways that are not well understood. In previous studies, we discovered GBM upregulates HIF-1α after temozolomide (TMZ) through an unknown mechanism independent of physiological hypoxia. We demonstrated HIF-1α but not HIF-2α knockdown reduces the stem-like properties of GBM and enhances their sensitivity to TMZ therapy in vitro and in vivo. To elucidate the mechanism of TMZ-induced HIF-1α stabilization, we performed co-immunoprecipitation of HIF-1α followed by mass spectrometry analysis (IP-MS). Our findings revealed 99 binding partners that were significantly and uniquely upregulated after TMZ treatment compared to GBM cells cultured under normal oxygen tension (20% O2), hypoxia (1% O2), or DMSO. Among these interactions, we focused on the HIF-1α-CAMKIIγ axis for further investigation based on pathway enrichment, patient survival data, and co-expression analysis in the TCGA_GBM dataset. Co-immunoprecipitation experiments confirmed enhanced binding between HIF-1α and CAMKIIγ in different GBM patient-derived xenograft (PDX) lines while this interaction was significantly reduced in normal astrocytes. Knockdown of CAMKIIγ inhibited the transcriptional activity of HIF-1α, increased its protein turnover, and improved TMZ sensitivity compared to control cells following TMZ treatment. Additionally, the expression of stem-cell markers and neurosphere formation, which are associated with GBM aggressiveness, were attenuated in hypoxia and TMZ conditions when CAMKIIγ was absent. Our data demonstrated that the HIF-1α-CAMKIIγ axis is critical for TMZ-induction of HIF signaling and cellular plasticity.