FOS and plasma cell myeloma: In particular, the decrease in the FOS expression level was found to be associated with cell death induced by the suppression of expression of Cyclin D1 and G0/G1 arrest in colorectal cancer cells and also with c-Jun/ATF2-mediated neuronal apoptosis, whereas JUN up-regulation was responsible for caspase activation and apoptosis induction in myeloma cells [41,42,43].