c-Myc-IMPDH1/2 axis promotes tumourigenesis by regulating GTP metabolic reprogramming

Metabolic reprogramming is a hallmark of cancer. Metabolic rate-limiting enzymes and oncogenic c-Myc (Myc) play critical roles in metabolic reprogramming to affect tumourigenesis. However, a systematic assessment of metabolic rate-limiting enzymes and their relationship with Myc in human cancers is lacking.

Multiple Pan-cancer datasets were used to develop the transcriptome, genomic alterations, clinical outcomes and Myc correlation landscapes of 168 metabolic rate-limiting enzymes across 20 cancers. Real-time quantitative PCR and immunoblotting were, respectively, used to examine the mRNA and protein of inosine monophosphate dehydrogenase 1 (IMPDH1) in human colorectal cancer (CRC), azoxymethane/dextran sulphate sodium-induced mouse CRC and spontaneous intestinal tumours from APC^Min/+ mice. Clone formation, CCK-8 and subcutaneous xenograft model were applied to investigate the possible mechanisms connecting IMPDH1 to CRC growth. Co-immunoprecipitation and protein half-life assay were used to explore the mechanisms underlying the regulation of IMPDH1.

We explored the global expression patterns, dysregulation profiles, genomic alterations and clinical relevance of 168 metabolic rate-limiting enzymes across human cancers. Importantly, a series of enzymes were associated with Myc, especially top three upregulated enzymes (TK1, RRM2 and IMPDH1) were positively correlated with Myc in multiple cancers. As a proof-of-concept exemplification, we demonstrated that IMPDH1, a rate-limiting enzyme in GTP biosynthesis, is highly upregulated in CRC and promotes CRC growth in vitro and in vivo. Mechanistically, IMPDH2 stabilizes IMPDH1 by decreasing the polyubiquitination levels of IMPDH1, and Myc promotes the de novo GTP biosynthesis by the transcriptional activation of IMPDH1/2. Finally, we confirmed that the Myc-IMPDH1/2 axis is dysregulated across human cancers.

Our study highlights the essential roles of metabolic rate-limiting enzymes in tumourigenesis and their crosstalk with Myc, and the Myc-IMPDH1/2 axis promotes tumourigenesis by altering GTP metabolic reprogramming. Our results propose the inhibition of IMPDH1 as a viable option for cancer treatment.