HP1a-mediated heterochromatin formation inhibits high dietary sugar-induced tumor progression.

High dietary sugar (HDS) is a modern dietary concern that involves excessive consumption of carbohydrates and added sugars, and increases the risk of metabolic disorders and associated cancers. However, epigenetic mechanisms by which HDS induces tumor progression remain unclear. Here, we investigate the role of heterochromatin, an important yet poorly understood part of the epigenome, in HDS-induced tumor progression of Drosophila Ras/Src and Ras/scrib tumor systems. We found that increased heterochromatin formation with overexpression of heterochromatin protein 1a (HP1a), specifically in tumor cells, not only decreases HDS-induced tumor growth/burden but also drastically improves survival of Drosophila with HDS and Ras/Src or Ras/scrib tumors. Moreover, HDS reduces heterochromatin levels in tumor cells. Mechanistically, we demonstrated that increased heterochromatin formation decreases wingless (wg) and Hippo (Hpo) signaling, thereby promoting apoptosis, via inhibition of Yorkie (Yki) nuclear accumulation and upregulation of apoptotic genes, and reduces DNA damage in tumor cells under HDS. Taken together, our work identified a novel epigenetic mechanism by which HP1a-mediated heterochromatin formation suppresses HDS-induced tumor progression likely by decreasing wingless and Hippo signaling, increasing apoptosis, and maintaining genome stability. Our model explains that the molecular, cellular, and organismal aspects of HDS-aggravated tumor progression are dependent on heterochromatin formation, and highlights heterochromatin as a therapeutic target for cancers associated with HDS-induced metabolic disorders.