Oncogenic RAS triggers stem cell: microenvironment crosstalk to drive malignant progression [ATAC-seq]

Oncogenic RAS/MAPK signaling drives metastatic squamous cell carcinomas (SCCs). These cancers are typified by high mutational burden, often featuring activating mutations in phosphatidylinositol-3-kinase (PI3K). Here we show that early in skin HRASG12V-induced oncogenesis, transitions from benign to malignant states are also marked by PI3K, this time super-activated through a temporal cascade of non-genetic events. Coupling clonal skin SCC genetic models with bulk and single-cell transcriptomics, chromatin-landscaping, lentiviral reporters, and lineage-tracing, we trace its roots. We show that following HRASG12V activation, oncogenic stem cells rewire their gene expression program. Initially, they produce an array of angiogenic factors, triggering a striking influx of vasculature and TGFß into the microenvironment. Sparked by TGFß-signaling, the stem cells induce leptin receptor (LEPR), which through the angiogenic influx activates LEPR-signaling to launch downstream PI3K-AKT-mTOR signaling. Our findings show how dynamic temporal crosstalk with the microenvironment, orchestrated by the stem cells, can drive the path to malignancy. Overall design: ATAC-seq was performed as described before in Buenrostro et al., 2013. Briefly, FACS sorted were lysed with ATAC lysis buffer on ice for 1 minute. Lysed cells were then tagmented with Tn5 transposase (Illumina) at 37C for 30min. Cleaned up fragments were PCR amplified (NEB) and size selected with 1.8X SPRI beads (Beckman Coulter). All libraries were sequenced on Illumina NextSeq 500 with 40-bp paired-end settings.