Persister state-directed transitioning and vulnerability in melanoma

Phenotypic heterogeneity and plasticity represent major drivers of tumor relapse in melanoma. Expression of the H3K4 demethylase and pRB-binding protein JARID1B/KDM5B follows a dynamic continuum across melanoma cells. Highly JARID1B-expressing cells are enriched after short-term drug treatment. However, under persistent drug-exposure, JARID1B heterogeneity is reconstituted. Using a doxycycline-titratable system and a novel chemical enhancer of JARID1B-expression, we found that JARID1Bhigh cells are transiently 'pseudo-differentiated'. Melanoma cells use this JARID1Bhigh growth-arrested state to survive drugs, but must decrease JARID1B expression again to re-enter cell cycling for long-term tumor repopulation. Overcoming the reversion to phenotypic heterogeneity by exogenous homogenization of the JARID1Bhigh phenotype causes tumor growth arrest, also in MAPKi-resistant melanoma. Mechanistically, JARID1B represents an integral checkpoint for coordinating cell differentiation via transcriptional control, stabilization of hypophosphorylated pRB, and attenuation of cytokinetic abscission. Thus, the plasticity among tumor differentiation states per se represents a novel therapeutic target, which can be chemically overcome. Overall design: RNAseq of melanoma cells (WM3734 and CSM152 treated with Cpd1 or control for 72h and WM3734Tet3G-KMD5B cells Doxycycline-induced for 24h, 48h or 72h) were analysed in triplicate using Illumina sequencer NextSeq 500.