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 G(1)-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 in vitro and in vivo 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.Abbreviations: 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.