The Janus-faced role of KDM5B heterogeneity in melanoma: differentiation as a situational driver of both growth arrest and drug-resistance

Phenotypic intratumoral heterogeneity and temporal transitions between cell differentiation states represent major drivers of tumor fitness in melanoma. Expression of the histone H3K4 demethylase KDM5B/JARID1B follows a highly dynamic equilibrium across melanoma cells. When challenged for example with targeted or cytotoxic drugs, the intrinsically slow-cycling KDM5Bhigh cell state becomes initially enriched, whereas under persistent drug-exposure melanomas decrease KDM5B expression again to re-enter cell proliferation for long-term tumor repopulation. However, the exact role of KDM5B for tumor cell differentiation and fate remained elusive so far. Here, we show that melanoma fitness can be overcome by molecular enforcement of high KDM5B expression levels. KDM5B-up-scaled melanoma cells are transcriptionally reprogramed towards a differentiated melanocytic profile including a slow-cycling state. This effect can be phenocopied by a newly identified chemical compound also leading to decelerated tumor growth. Mechanistically, KDM5B represents a checkpoint for coordinating the differentiation phenotype of melanoma cells via transcriptional reprograming, cell cycle delay, and attenuation of cytokinetic abscission. These findings indicate that tumor plasticity per se, i.e. the necessity of cancer cells to dynamically switch between different cell cycling and differentiation states, represents an important oncologic process that can be chemically overcome.