RNF8 stabilizes MYC via K63‐linked ubiquitination to promote metabolic reprogramming in triple‐negative breast cancer

Abstract

Triple-negative breast cancer (TNBC) is the most lethal subtype of breast cancer owing to its aggressive nature and the lack of targeted therapy for most patients. MYC, an oncogenic transcription factor, is elevated in TNBC and causes accelerated tumor growth through metabolic reprogramming. However, there is currently no drug available in clinics to inhibit MYC. Ring Finger Protein 8 (RNF8), an E3 ubiquitin ligase, is highly expressed in TNBC and essential for tumor progression. To comprehensively understand the role of RNF8 in TNBC, we conducted RNA-sequencing and found that the downregulation of RNF8 attenuates the activity of the MYC network in human TNBC cell lines. Moreover, we observed the reduced glucose uptake and utilization in TNBC cells with RNF8 knockdown as a result of the decreased expression of MYC and its target genes such as glucose transporter GLUT1 and key glycolytic enzyme HK2. Knockdown of RNF8 also decreased the metabolic influx in the glycolysis pathway as revealed in the isotope tracer studies coupled with mass spectrometry analysis. Importantly, the treatment of proteasome inhibitor MG132 was able to restore MYC protein expression, while cycloheximide chase assay showed that MYC protein has a shorter half-life in TNBC cells with RNF8 deficiency. In vivo ubiquitination assay further demonstrated that RNF8 mediates Lysine (K)63-linked ubiquitination over MYC, suggesting that RNF8 mediates K63-linked ubiquitination to stabilize MYC against proteasomal degradation. Taken together, these results suggest that RNF8 enhances MYC signaling, thereby promoting metabolic reprogramming and tumor progression in TNBC. Targeting RNF8 may be a reasonable alternative to inhibit MYC-driven cancers such as TNBC.