MAP3K5 and viral infectious disease: Upon viral infection, Fbxo21 ubiquitylates and activates apoptosis signal-regulating kinase 1 (ASK1), a protein with pivotal roles in stress and immune responses, thereby leading to the activation of c-Jun N-terminal kinases (JNK1/2) and p38 MAPKs downstream signaling149 (Fig. 5b).