Phenotypic heterogeneity of solid cancer plays a critical role in shaping treatment response. This type of heterogeneity is organized spatially with specific phenotypes, such as distinct clusters of proliferating and cell cycle-arrested cells within a tumor. What determines the occurrence of these phenotypically distinct domains in solid cancers is poorly understood. Utilizing in vitro and in vivo three-dimensional models, we show that in melanoma spatial organization of phenotypic heterogeneity is dictated by the expression and activity of the lineage-survival oncogene MITF. Mechanistically, we reveal that MITF controls extracellular matrix (ECM) composition and decreases ECM organization. This leads to reduction of Rho-ROCK-myosin signaling-driven mechanotransduction through poor focal adhesion maturation and reduced contractility of the actin cytoskeleton. The resulting altered tumor microarchitecture and structural relaxation decrease tumor solid stress and subsequently p27Kip1 expression, ultimately reducing phenotypic heterogeneity. Consequently, selective inhibition of ROCK phenocopies the effect of MITF overexpression, demonstrating the importance of cell-ECM crosstalk in this process.

In summary, our findings place tumor cell-ECM crosstalk resulting in altered tumor microarchitecture and ROCK-driven mechanotransduction as a central driver of phenotypic tumor heterogeneity. Melanoma shares these physical properties with other solid cancers underscoring the potential for therapeutically targeting this phenomenon in cancer, beyond melanoma.