Cancer cells respond to hypoxia by upregulating the hypoxia-inducible factor 1α (HIF1A) transcription factor, which drives survival mechanisms that include metabolic adaptation and induction of angiogenesis by VEGF. Pancreatic tumors are poorly vascularized and severely hypoxic. To study the angiogenic role of HIF1A, and specifically probe whether tumors are able to use alternative pathways in its absence, we created a xenograft mouse tumor model of pancreatic cancer lacking HIF1A. After an initial delay of about 30 days, the HIF1A-deficient tumors grew as rapidly as the wild-type tumors and had similar vascularization. These changes were maintained in subsequent passages of tumor xenografts in vivo and in cell lines ex vivo. There were many cancer cells with a "clear-cell" phenotype in the HIF1A-deficient tumors; this was the result of accumulation of glycogen. Single-cell RNA sequencing (scRNA-seq) of the tumors identified hypoxic cancer cells with inhibited glycogen breakdown, which promoted glycogen accumulation and the secretion of inflammatory cytokines, including interleukins 1β (IL1B) and 8 (IL8). scRNA-seq of the mouse tumor stroma showed enrichment of two subsets of myeloid dendritic cells (cDC), cDC1 and cDC2, that secreted proangiogenic cytokines. These results suggest that glycogen accumulation associated with a clear-cell phenotype in hypoxic cancer cells lacking HIF1A can initiate an alternate pathway of cytokine and DC-driven angiogenesis. Inhibiting glycogen accumulation may provide a treatment for cancers with the clear-cell phenotype. SIGNIFICANCE: These findings establish a novel mechanism by which tumors support angiogenesis in an HIF1α-independent manner.
©2019 American Association for Cancer Research.