UC San Diego

As Oral Squamous Cell Carcinoma’s (OSCC) patients’ survival rate significantly decreases with metastasis, risk factors that can enhance OSCC metastasis should be identified and targeted. In this thesis, metastasis-inducing tumor-TME interaction is categorized into two – cell-extra-cellular matrices (ECM) and intra-tumor heterotypic cell-cell interaction – and studied Tumor Matrix stiffening is ubiquitous in solid tumors and can direct epithelial-mesenchymal transition (EMT) and cancer cell migration. Stiffened niche can even cause poorly invasive oral squamous cell carcinoma (OSCC) cell lines to acquire a less adherent, more migratory phenotype, but mechanisms and durability of this acquired “mechanical memory” are unclear. Here, we observed that contractility and its downstream signals could underlie memory acquisition; invasive SCC25 cells overexpress myosin II (vs. non-invasive Cal27 cells) consistent with OSCC. However, prolonged exposure of Cal27 cells to a stiff niche or contractile agonists upregulated myosin and EMT markers and enabled them to migrate as fast as SCC25 cells, which persisted even when the niche softened and indicated “memory” of their prior niche. Stiffness-mediated mesenchymal phenotype acquisition required AKT signaling and was also observed in patient samples, whereas phenotype recall on soft substrates required focal adhesion kinase (FAK) activity. Phenotype durability was further observed in transcriptomic differences between pre-conditioned Cal27 cells cultured without or with FAK or AKT antagonists, and such transcriptional differences corresponded to discrepant patient outcomes. Tumor is made up of heterotypic cell populations and they can interact to affect each other’s behavior. OSCC showed response to cytokines from immune cells, but such cell-cell interaction within tumor has not been studied enough. Two heterotypic OSCC cell lines with different invasiveness – SCC25 and Cal27 – are indirectly co-cultured in this study to observe paracrine cell signaling between two cell lines. Cultured with SCC25-conditioned media (CM), Cal27 showed enhanced cell migration and transcriptomic changes related to cytokine response. SCC25-CM had higher expression of IL-1a, IL-6, IL-8, Angiogenin and PAI-1, and supplementing normal growth media with those cytokines comparatively increased Cal27’s motility. In response to the cytokines rich in SCC25-CM, Cal27 activate MAPK and AKT signaling pathways, and inhibition of those pathways disturbed cell migration enhancement by paracrine cell signaling.