LRRC4 Act As a Novel Autophagy Inhibitor that Restores Sensitivity of GBMs to Temozolomide

Background: Leucine-rich repeat containing 4(LRRC4) is low expression in GBM and our group first confirmed a new function of LRRC4 as a tumour suppressor for glioma. However, the underlying molecular mechanism and pathobiology of LRRC4 in autophagy and Temozolomide (TMZ) resistance remains largely unknown. Methods: TCGA date was used to examine the relationship between LRRC4 and autophagy element. LRRC4-overexpressing GBM cells were evaluated for autophagy level and TMZ resistance using cell-based functional assays and a mouse xenograft model. Furthermore, co-immunoprecipitation (CoIP) and mass spectrometry (MS) and were performed to identify the interaction partners of LRRC4. Findings: We confirmed the critical role of LRRC4 in regulation of autophagy. Ectopic expression of LRRC4 in GBM cells abrogates cells autophagy level and increases cell apoptosis when treated with TMZ. LRRC4 was associated with the DEPTOR/mTOR complex, and this interaction resulted in autophagy inhibition. Combined LRRC4 expression and TMZ treatment prolonged the survival of mice with tumour xenografts. Furthermore, the levels of LRRC4, DEPTOR and autophagy are clinically relevant for GBM. Interpretation: Our findings revealed that LRRC4 directly binds to DEPTOR and induces its degradation, thereby inhibiting cell autophagy. Moreover, autophagy inhibition increased the treatment efficacy of TMZ in glioma, and LRRC4-expressing cells underwent increased apoptosis with TMZ treatment, indicating that LRRC4 is likely to have significant potential as a therapeutic marker and target for TMZ treatment in glioma patients. Funding Statement: This works was supported by the National Natural Science Foundation of China (Grant No. 81874150) and Graduate Student Research Innovation Project in Hunan Province (2019zzts084). Declaration of Interests: The authors declare that they have no competing interests. Ethics Approval Statement: All of the protocols were reviewed by the Joint Ethics Committee of the Central South University Health Authority and performed following national guidelines. All animal experiments were approved by the Animal Care and Use Committee of Central South University.