RUNX2 and osteosarcoma: Interaction between overexpressed RUNX2 and the protein product of proto-oncogene FOS, whose overexpression in mice led to development of the first osteosarcoma mouse model [163], upregulates transcription of the metastasis-associated gene MMP13 via transcription factor AP-1 [164] and has potential for other roles in oncogenesis [165].