Matrix softness regulates plasticity of tumour-repopulating cells via H3K9 demethylation and Sox2 expression

TLDR

Tumour‑repopulating cells are a self‑renewing, tumorigenic subpopulation that exhibit low H3K9 methylation insensitive to matrix stiffness, and soft 3D gels enhance their growth. The study investigates how TRCs maintain self‑renewal, focusing on the role of H3K9 methylation and Sox2. H3K9 methylation at the Sox2 promoter suppresses Sox2 expression, which is essential for TRC self‑renewal and tumorigenicity in vitro and in vivo. TRCs display plasticity in mechanical stiffening, H3K9 methylation, and Sox2 expression; reducing H3K9 methyltransferases or softening the matrix increases Sox2‑dependent self‑renewal, indicating that 3D soft‑fibrin‑matrix‑mediated demethylation and Sox2 activation drive TRC self‑renewal.

Abstract

Tumour-repopulating cells (TRCs) are a self-renewing, tumorigenic subpopulation of cancer cells critical in cancer progression. However, the underlying mechanisms of how TRCs maintain their self-renewing capability remain elusive. Here we show that relatively undifferentiated melanoma TRCs exhibit plasticity in Cdc42-mediated mechanical stiffening, histone 3 lysine residue 9 (H3K9) methylation, Sox2 expression and self-renewal capability. In contrast to differentiated melanoma cells, TRCs have a low level of H3K9 methylation that is unresponsive to matrix stiffness or applied forces. Silencing H3K9 methyltransferase G9a or SUV39h1 elevates the self-renewal capability of differentiated melanoma cells in a Sox2-dependent manner. Mechanistically, H3K9 methylation at the Sox2 promoter region inhibits Sox2 expression that is essential in maintaining self-renewal and tumorigenicity of TRCs both in vitro and in vivo. Taken together, our data suggest that 3D soft-fibrin-matrix-mediated cell softening, H3K9 demethylation and Sox2 gene expression are essential in regulating TRC self-renewal. Soft 3D gels can promote the growth of tumour-repopulating cells, a self-renewing subpopulation of cancer cells critical in cancer progression. Here, the authors investigate the mechanism behind this phenomenon and show that the histone 3 lysine residue 9 methylation and Sox2 are controlling this process.