Impact of an Alu insertion on the cellular localisation of tissue factor protein

Tissue Factor (Hugo Gene Nomenclature Consortium HGNC gene Factor III (F3)) plays vital roles in many cellular processes including haemostasis, thrombosis, inflammation and angiogenesis. Approximately 30-40 million years ago, an inverted Alu element inserted into the F3 3'-UTR, and we hypothesised that this altered post-translational intra-cellular trafficking of F3 protein. Confocal microscopy of MDA-MB-231 human breast cancer cells using fluoroprobe constructs regulated by the F3 3'-UTR with or without the Alu insertion demonstrated that the presence of the Alu element promoted protein localisation to the Golgi, and reduced cell membrane localisation. Furthermore, stimulation of cells with a Protease-Activated Receptor-2 activating peptide led to rapid mobilisation of the fluorophore from the Golgi to the cell surface. These findings suggest that the Alu insertion facilitates Golgi retention of F3 and mobilisation to the cell surface upon demand. This mechanism may provide an evolutionary advantage by fine-tuning the cellular haemostatic response in primates.