Surviving Stress with the Tumour Microenvironment: Understanding Complex Cell - Cell Interactions

Each year more than 18 million people are diagnosed with cancer. Stress survival plays a key role in tumour resistance which is a leading cause of cancer deaths. Understanding how cells respond to stress is key to understanding and treating cancer. Within a tumour, cells interact with many other cell types in the surrounding tumour microenvironment. The tumour microenvironment acts to both assist and resist tumorigenesis and metastasis depending on these cellular interactions.

Rho Zero cells are cells that contain no mitochondrial DNA and therefore lack a functional electron transport chain and rely on glycolysis for energy metabolism, these cells require supplementation to survive in cell culture. When deprived of essential supplementation rho zero cells exhibit severe metabolic stress. Yet when implanted into mice they form tumours after a 2-3 week delay. After this they contain new mitochondrial DNA acquired from the tumour microenvironment.

This thesis explored how cells under stress interact with a model tumour microenvironment and exploit normal cellular processes for continued survival. Using confocal microscopy, IncuCyte microscopic videography, and MinION sequencing techniques we have established that rho zero cells under metabolic stress in a co-culture environment uptake mitochondrial DNA from the surrounding microenvironment and that this cell survival is contact associated. Nars1 was identified as a potential signal from the rho zero cells to the tumour microenvironment when placed under metabolic stress. This identified Nars1 as potential part of a novel stress response mechanism for severe metabolic stress. I then investigated if these findings could be replicated in cisplatin and doxorubicin treated wild type cells. While contact dependant survival was implied in the doxorubicin treated cells no Nars1 signal was found. However, an up-regulation of Cxcl5 and Cxcl1 was identified as a commonly up-regulated transcript between the rho zero and both chemotherapy treatments in 4T1 breast cancer implicating a conserved chemokine signalling response to stress.

Together these results illustrate the importance of chemokine signalling in complex cellular interactions as part of a cellular survival stress response.