Cell state diversity promotes metastasis through heterotypic cluster formation in melanoma

Abstract

In melanoma, transcriptional profiling has revealed multiple co-existing cell states, including proliferative versus invasive sub-populations that have been posited to represent a "go or grow" tradeoff. Both of these populations are maintained in tumors, but how they physically interact to promote metastasis is unknown. We 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 clusters with a rim of PRO cells. Intravital imaging demonstrated cooperation between these populations, in which the INV cells facilitated the spread of less metastatic PRO cells. We identified the TFAP2 neural crest transcription factor as a master regulator of both clustering and the PRO/INV states. Our data suggest a framework for the co-existence of these two divergent cell populations, in which differing cell states form heterotypic clusters that promote metastasis via cell-cell cooperation.

TFAP2 paralogs facilitate chromatin access for MITF at pigmentation genes but inhibit expression of cell-cell adhesion genes independently of MITF

“…The expression of genes promoting cell migration and invasion has been observed to be higher in cells with low versus high MITF activity (Rambow et al, 2019). Indeed we show evidence suggesting that TFAP2 paralogs directly suppress such genes, consistent with our previous findings (Campbell et al, 2021). Thus, independent of its other activities as a transcription factor, TFAP2 determines which genes can be activated by MITF.…”

“…13D ). This finding also contrasts with the observation that the expression tfap2e correlates negatively with the migratory capacity of zebrafish models of melanoma (Campbell et al, 2021), but it is consistent with the accumulation of melanocytes in the dorsum of zebrafish tfap2a knockout embryos (Barrallo-Gimeno et al, 2004; Knight et al, 2004; Knight et al, 2003) and tfap2a/ tfap2e double mutant embryos ( Fig. 1 , Supplemental Fig.S1 ).…”

“…Finally, we considered how TFAP2 paralogs might regulate the phenotype in melanoma cells. Advanced melanoma is characterized by lower levels of TFAP2A than benign nevi (e.g., Huang et al, 1998), and low transcript levels of tfap2 paralogs are associated with an invasive phenotype in zebrafish melanoma (Campbell et al, 2021). We examined the association of TFAP2-activated and TFAP2-repressed genes ( Supplemental Fig.…”

“…For instance, in zebrafish tfap2a loss-of-function mutant embryos the number of melanocytes is lower than normal and pigmentation is profoundly delayed relative to in wild type embryos; this phenotype is exacerbated if tfap2a mutant embryos are also depleted of tfap2e expression with antisense morpholinos (Van Otterloo et al, 2010). In zebrafish melanoma Tfap2a and Tfap2e also appear to act redundantly to promote proliferation and, interestingly, to suppress cell adhesion and cell migration (Campbell et al, 2021). Consistent with redundant function of Tfap2 paralogs in the melanocyte lineage, in the skin of mouse embryos with neural-crest specific knockout of the two paralogs with highest expression, Tfap2a and Tfap2b , there are fewer-than-normal cells expressing markers of melanocytes (Seberg et al, 2017b).…”

Metastasis-Initiating Cells and Ecosystems

“…CTC clusters may also include tumor-derived stromal cells (28). CTC clustering provides intercellular spaces that concentrate paracrine growth-promoting signals (29), and enable cooperation between different cancer cell states within a cluster (30). CTC clusters are enriched in genome methylation patterns that denote a stem-like cancer cell state (31), and therefore have features of MICs.…”