MERTK and head and neck squamous cell carcinoma: Out of these cell lines, two were selected as models in which to probe Tyro3 function; one of these was SCC-25 head and neck squamous cell carcinoma cells, which express both Axl and Tyro3 but not MerTK, whilst the other, MGH-U3 bladder carcinoma cells, expresses Tyro3 as a sole TAM receptor.