UC Riverside

Cancer is the second leading cause of global mortality. Accumulating evidence strongly suggests that aberrant alterations in signaling cascades can lead to uncontrolled cell growth, driving the progression of this disease. While the promotion of cancer cell growth by hyperglycemia has been extensively studied, the comprehensive mechanism underlying this relationship remains incompletely elucidated. In the current study, we present findings that high glucose levels (HG) indeed bolster DNA synthesis and cell cycle progression, fostering tumor cell growth, as revealed by genome-wide analyses. Moreover, our investigation identified E2F family as the central transcription factor responsible for the adaptive response induced by HG. The use of the pan-E2F inhibitor HLM006474 and shRNA-mediated E2F1 depletion, effectively counteracted HG-triggered DNA synthesis and cell growth. Furthermore, we establish that HG amplifies Rb1 phosphorylation, directly contributing to the activation of E2F1. Inhibition of Rb1 phosphorylation using the CDK2/4/6 inhibitor compound PF-3600 substantially mitigates the E2F1-mediated transcriptional activation of downstream DNA replication genes. Notably, among the E2F1 target genes induced by HG, RRM2 plays an essential role in the nucleotide synthesis by generating essential dNTPs required for DNA replication. Our investigation reveals that HG promotes intracellular dNTP levels in an E2F1-RRM2-dependent manner, closely associated with increased DNA synthesis and subsequent cancer cell growth. The RNR inhibitor Triapine effectively impedes RRM2-mediated elevation of intracellular dATP and dGTP, and DNA synthesis. To gain more insights into the metabolic alterations occurring in HG-treated cancer cells, we carried out the untargeted metabolomic profiling. This analysis not only reaffirms the activation of glycolysis in HG-treated cells, as evidenced by the elevated levels of lactic acid, but also illustrates noteworthy enhancements in the levels of sucrose and fructose in the polyol pathway. These findings provide another facet of how cancer cells utilize excess glucose to fuel their proliferation. Collectively, our findings decipher the oncogenic signaling and metabolic connections between hyperglycemia and cancer cell proliferation, mediated through the Rb1/E2F and polyol pathways. This study provides a detailed molecular mechanism that sheds light on how hyperglycemia directs tumor cells to enhanced cell cycle progression and cell proliferation.