Activation of chaperone-mediated autophagy suppresses glioblastoma by promoting wild-type IDH1/isocitrate dehydrogenase 1 degradation

Glioblastoma is the most aggressive form of primary brain malignancy and is defined as IDH/isocitrate dehydrogenase wild-type tumors. Upregulation of IDH1 is associated with poor prognosis; however, the mechanisms that regulate IDH1 expression in glioblastoma pathogenesis are poorly understood. In this study, we identified chaperone-mediated autophagy (CMA) as a critical regulator of IDH1 in glioblastoma progression. We determined that wild-type IDH1 contained a conserved CMA-targeting motif and directly interacted with the CMA chaperone HSPA8/HSC70 (heat shock protein family A (Hsp70) member 8). Our findings indicated that genetic or pharmacological inhibition of CMA resulted in IDH1 accumulation, which in turn increased α-ketoglutarate (α-KG) production. This metabolic shift upregulated CCND1 (cyclin D1), disrupted the RB1 (RB transcriptional corepressor 1) cell cycle checkpoint, and accelerated the G₁-S phase transition, thereby promoting tumor growth. Analysis of clinical glioma specimens revealed widespread CMA dysfunction concurrent with IDH1 overexpression. This phenotype was further exacerbated by chronic temozolomide treatment in both <i>in vitro</i> and <i>in vivo</i> glioblastoma models. Notably, CMA-activating compounds, including the RARA (retinoic acid receptor alpha) antagonist CA77.1, the class I phosphoinositide 3-kinase (PI3K) inhibitor paxalisib, and metformin, effectively reduced IDH1 and CCND1 levels while suppressing glioblastoma cell growth. Together, our findings suggest that dysfunction of the CMA-IDH1-CCND1 regulatory cascade drives progression of IDH1-wild-type glioblastoma and provide a mechanistic basis for repurposing CMA activators as potential therapeutic agents for these tumors.<b>Abbreviations:</b> α-KG: α-ketoglutarate; CCND1: cyclin D1; CMA: chaperone-mediated autophagy; E2F1: E2F transcription factor 1; GSC: glioblastoma stem cells; HSPA8/HSC70: heat shock protein family A (Hsp70) member 8; LAMP1: lysosomal associated membrane protein 1; LAMP2A: lysosomal associated membrane protein 2A; IDH1: isocitrate dehydrogenase (NADP(+)) 1; PI3K: phosphoinositide 3-kinase; RARA: retinoic acid receptor alpha; RB1: RB transcriptional corepressor 1; TMZ: temozolomide.