Cell State Diversity Promotes Metastasis Through Heterotypic Cluster Formation In Melanoma

Metastasis is the primary cause of cancer death, yet we know little about what determines its timing and aggressiveness. In melanoma, transcriptional profiling has revealed multiple co-existing cell states, including proliferative (PRO) versus invasive (INV) subpopulations that have been posited to represent a “go or grow” tradeoff in the etiology of metastasis. Although both of these populations are present in primary tumors and metastases, little is known about how they physically interact with each other in tumor dissemination. We use a combination of melanoma modeling in zebrafish and human validation to demonstrate that these subpopulations form spatially structured heterotypic clusters that cooperate in the seeding of metastasis. We unexpectedly found that INV cells were tightly adherent to each other and formed large tumor cell clusters. Mixing of PRO and INV cells generated heterotypic clusters, composed of a dense central core of INV cells surrounded by a rim of PRO cells. Using intravital imaging, we identified metastatic cooperation between these two subpopulations, in which the INV cells facilitated the earlier spread of the less metastatic PRO cells via collective extravasation. Mechanistically, we identified the TFAP2 family of neural crest transcription factors to be a master regulator of both clustering and the PRO/INV states. Knockout of TFAP2 from melanoma cells reduced proliferation but increased clustering and metastasis. TFAP2 loss resulted in increased expression of cell adhesion molecules, providing a mechanistic basis for cluster formation. Our data suggest a coherent framework for the co-existence of these two divergent cell populations in melanoma, in which differing cell states form heterotypic clusters that promote collective metastasis via cell-cell cooperation. Citation Format: Nathaniel R. Campbell, Maomao Zhang, Maayan Baron, Silja Heilmann, Maxime Deforet, Lorenza Ferretti, Ting-Hsiang Huang, Mitchell P. Levesque, Itai Yanai, Joao B. Xavier, Richard M. White. Cell state diversity promotes metastasis through heterotypic cluster formation in melanoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1107.