The pentose phosphate pathway (PPP) plays a critical role in macromolecule biosynthesis and maintaining cellular redox homoeostasis in rapidly proliferating cells. Upregulation of the PPP has been shown in several types of cancer. However, how the PPP is regulated to confer a selective growth advantage on cancer cells is not well understood. Here we show that glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme of the PPP, is dynamically modified with an O-linked β-N-acetylglucosamine sugar in response to hypoxia. Glycosylation activates G6PD activity and increases glucose flux through the PPP, thereby providing precursors for nucleotide and lipid biosynthesis, and reducing equivalents for antioxidant defense. Blocking glycosylation of G6PD reduces cancer cell proliferation in vitro and impairs tumor growth in vivo. Importantly, G6PD glycosylation is increased in human lung cancers. Our findings reveal a mechanistic understanding of how O-glycosylation directly regulates the PPP to confer a selective growth advantage to tumours.

Purpose: Here, we have investigated treatment resistance mechanisms in small cell lung cancer (SCLC) by focusing on comparing the genotype and phenotype in tumor samples of treatment-resistant and treatment-sensitive SCLC. Experimental Design: We conducted whole-exome sequencing on paired tumor samples at diagnosis and relapse from 11 patients with limited-stage (LS)-SCLC and targeted sequencing of 1,021 cancer-related genes on cell-free DNA at baseline and paired relapsed samples from 9 additional patients with LS-SCLC. Furthermore, we performed label-free mass spectrometry–based proteomics on tumor samples from 28 chemo-resistant and 23 chemo-sensitive patients with extensive-stage (ES)-SCLC. The main findings were validated in vitro in chemo-sensitive versus chemo-resistant SCLC cell lines and analyses of transcriptomic data of SCLC cell lines from a public database. Results: Genomic analyses demonstrated that at relapse of LS-SCLC, genes in the PI3K/AKT signaling pathway were enriched for acquired somatic mutations or high-frequency acquired copy-number variants. Pathway analysis on differentially upregulated proteins from ES-SCLC cohort revealed enrichment in the HIF-1 signaling pathway. Importantly, 7 of 62 PI3K/AKT pathway genes containing acquired somatic copy-number amplifications were enriched in HIF-1 pathway. Analyses of transcriptomic data of SCLC cell lines from public databases confirmed upregulation of PI3K/AKT and HIF-1 pathways in chemo-resistant SCLC cell lines. Furthermore, chemotherapy-resistant cell lines could be sensitive to PI3K inhibitors in vitro. Conclusions: PI3K/AKT pathway activation may be one potential mechanism underlying therapeutic resistance of SCLC. This finding warrants further investigation and provides a possible approach to reverse resistance to chemo/radiotherapy.

No abstract