FOS and viral infectious disease: The transcriptional activity of c-Jun/AP-1 is modulated by a wide variety of cellular and extracellular cues, including growth factors, bacterial and viral infection, cytokines, chemokines, hormones, ultraviolet (UV) irradiation, cellular and environmental stresses (e.g., hypoxia), thereby affecting the homeostasis of AP-1 within cells (Figure 1A).