Abstract
A desynchronized circadian rhythm in tumors is coincident with aberrant inflammation and dysregulated metabolism. As their interrelationship in cancer etiology is largely unknown, we investigated the link among the three in glioma. The tumor metabolite lactate-mediated increase in the proinflammatory cytokine interleukin-1β (IL-1β) was concomitant with elevated levels of the core circadian regulators Clock and Bmal1. Small interfering RNA (siRNA)-mediated knockdown of Bmal1 and Clock decreased (i) lactate dehydrogenase A (LDHA) and IL-1β levels and (ii) the release of lactate and proinflammatory cytokines. Lactate-mediated deacetylation of Bmal1 and its interaction with Clock regulate IL-1β levels and vice versa. Site-directed mutagenesis and luciferase reporter assays indicated the functionality of E-box sites on LDHA and IL-1β promoters. Sequential chromatin immunoprecipitation (ChIP-re-ChIP) revealed that lactate-IL-1β cross talk positively affects the corecruitment of Clock-Bmal1 to these E-box sites. Clock-Bmal1 enrichment was accompanied by decreased H3K9me3 and increased H3K9ac and RNA polymerase II (Pol II) occupancy. The lactate-IL-1β-Clock (LIC) loop positively regulated the expression of genes associated with the cell cycle, DNA damage, and cytoskeletal organization involved in glioma progression. TCGA (The Cancer Genome Atlas) data analysis suggested the presence of lactate-IL-1β cross talk in other cancers. The responsiveness of stomach and cervical cancer cells to lactate inhibition followed the same trend as that exhibited by glioma cells. In addition, components of the LIC loop were found to be correlated with (i) patient survival, (ii) clinically actionable genes, and (iii) anticancer drug sensitivity. Our findings provide evidence for potential cancer-specific axis wiring of IL-1β and LDHA through Clock-Bmal1, the outcome of which is to fuel an IL-1β-lactate autocrine loop that drives proinflammatory and oncogenic signals.