Panoply™ Human MYC Knockdown Stable Cell Line

Head and neck squamous cell carcinoma (HNSCC) is highly dependent on glutamine catabolism. Targeting this metabolic dependence has become a potential therapeutic approach for HNSCC. Here, researchers performed bioinformatics analysis on the TCGA HNSCC cohort, revealing a significant correlation between the expression of MYC (encoding c-Myc protein) and GLS1 (the catalytic enzyme in the first step of glutamine catabolism). Interestingly, disrupting the GLS1 signaling pathway in HNSCC cells through gene knockout or CB-839 treatment led to decreased c-Myc protein stability, which was achieved via the USP1-dependent ubiquitin-proteasome pathway. On the other hand, c-Myc can directly bind to the promoter region of GLS1 and upregulate its transcription. Notably, the GLS1-c-Myc pathway enhances ACC-dependent SLUG acetylation, thereby promoting cancer cell invasion and metastasis. Therefore, the GLS1-c-Myc axis is considered a key positive feedback loop driving the invasiveness of head and neck squamous cell carcinoma (HNSCC). In terms of treatment, the combination of CB-839 and the c-Myc inhibitor MYCi975 significantly inhibited the GLS1-c-Myc signaling pathway, and its anti-tumor effect was superior to that of single drugs in an orthotopic mouse model of HNSCC. These findings are expected to provide new insights into the effective treatment of HNSCC patients, addressing the urgent needs arising from the high incidence and metastasis rate of this disease.

c-Myc is a multifunctional transcription factor that exhibits significant co-expression with GLS1 in head and neck squamous cell carcinoma (HNSCC). Blocking the c-Myc signaling pathway using the c-Myc inhibitor MYCi975 or shRNA significantly inhibited cellular glutamine depletion (Figure 1A and B). MYCi975 treatment led to dose-dependent degradation of c-Myc, while simultaneously reducing GLS1 levels in HN6 and HN12 cells (Figure 1C). The same trend in GLS1 levels was observed in MYC knockdown cells (Figure 1D), confirmed by RT-qPCR analysis (Figure 1E). MYC overexpression enhanced GLS1 levels in HN6 and HN12 cells (Figure 1F), indicating that c-Myc plays a regulatory role in GLS1 expression. Promoter analysis identified an E-box sequence located between -1218 and -1229 bp upstream of the GLS1 gene promoter (Figure 1G). ChIP-qPCR results showed significant c-Myc binding at the GLS1 gene promoter in both HN6 and HN12 cells (Figure 1H). In MYC knockdown cells, Slug protein levels were significantly reduced, and this reduction was even more pronounced in the presence of CB-839 (Figure 1I). Compared to control cells, Slug acetylation levels were persistently reduced in Slug-overexpressing and MYC-knockdown HN6 and HN12 cells, and this effect was significantly enhanced in the presence of CB-839 (Figure 1J). Furthermore, MYC knockdown was more effective in inhibiting HNSCC cell invasion in the presence of CB-839 (Figure 1K). These data indicate that reducing c-Myc mRNA and protein levels can more effectively block the Slug signaling pathway.

Figure 1. MYC knockdown reduces GLS1 expression and is more potent in suppressing Slug acetylation and HNSCC cell invasion in the presence of CB-839. (Yang J, et al., 2024)