Cell‐cell interactions in tumour progression

Abstract

Background: When EMT arises in carcinomas, it is often localised, the tumours being composed of both cells that have undergone an EMT, and cells that have retained epithelial characteristics. We hypothesised that these two cancer cell populations can cooperate to increase malignancy. Aim: To test Snail2 and the G12V mutant form of Hras for the ability to cooperate to increase malignancy when they are present in different clones. Methods: Snail2 and Hras were expressed in head and neck squamous cell carcinoma (HNSCC) cells as fluorescent protein fusions, enabling us to follow the behaviour of individual populations of cells when they were present as mixtures. Live-cell and end-point assays were used to study cell proliferation, migration and invasion in vitro and tumour growth and dissemination in vivo, following subcutaneous injection into nude mice. Results: HNSCC cells that expressed Snail2 exhibited decreased cell-cell adhesion and increased migration and invasion of extracellular matrix in vitro. In vivo, they were unable to form tumours, but disseminated to draining lymph nodes from the site of injection. Hras increased cell proliferation, but did not cause an EMT. Hras enabled the formation of tumours in vivo that failed to disseminate. In mixed populations, Hras cells imparted their enhanced growth property onto neighbouring cells and Snail2 enhanced the invasiveness of neighbouring cells. In vivo, Hras-expressing cells enabled Snail2-expressing cells to form part of the tumour. Furthermore, tumours that grew from mixtures of Snail2-expressing and Hras-expressing cells grew faster than those formed from cells that express both genes. Conclusion: In carcinomas that have genetically diverse cell populations, the cells that undergo an EMT can interact with cells that do not undergo an EMT, leading to a collective population that is more malignant than the subpopulations that comprise it.