JunB is a member of the Jun family of proteins, which belongs to the larger group of transcription factors known as the AP-1 (Activator Protein 1) complex. AP-1 complexes are dimers composed of Jun (c-Jun, JunB, JunD) and Fos (c-Fos, FosB, Fra1, Fra2) proteins. These dimers regulate gene expression by binding to specific DNA sequences called AP-1 response elements in the promoter regions of target genes. JunB plays a crucial role in cell proliferation, differentiation, apoptosis, and other cellular processes. It can function as both a transcriptional activator and repressor, depending on the cellular context and the interacting proteins. JunB is also involved in regulating the immune response and inflammation. In cancer research, JunB has been found to have both tumor-suppressing and tumor-promoting roles. It can act as a tumor suppressor by inhibiting cell proliferation and promoting apoptosis, but it can also promote tumor growth and invasion by activating genes that are involved in cell migration and invasion. The expression and activity of JunB are tightly regulated by various signaling pathways, including the MAPK (Mitogen-Activated Protein Kinase) pathway. Aberrant JunB expression or activity has been associated with a variety of diseases, including cancer, autoimmune diseases, and inflammatory disorders.