cJun

c-Jun, also written cJun, is a transcription factor encoded by the JUN gene in humans. It is a key component of the activator protein 1 (AP-1) transcription factor complex, forming homodimers or heterodimers with other members of the JUN or FOS families, such as c-Fos or FosB. The protein contains a basic region leucine zipper (bZIP) domain that mediates DNA binding to the AP-1 consensus sequence TGAC/GTCA and dimerization, enabling combinatorial control of target genes.

Activation and regulation: c-Jun activity is driven by mitogen-activated protein kinase (MAPK) pathways, especially the c-Jun N-terminal kinase (JNK) pathway. Phosphorylation at serine residues 63 and 73 increases transcriptional activity and stability. c-Jun can be additionally regulated by other signaling inputs and post-translational modifications, including ubiquitination and acetylation, which influence its turnover and cofactor recruitment.

Functions and roles: As a transcription factor, c-Jun controls expression of genes involved in cell proliferation, differentiation, survival, and apoptosis in response to stress, cytokines, and growth factors. It participates in diverse biological processes, including development, wound healing, immune responses, and neuronal function. The specific outcome of c-Jun activity depends on dimer composition, cellular context, and cooperating cofactors.

Clinical relevance: Deregulation of c-Jun/AP-1 signaling has been linked to cancer, where AP-1 can promote or suppress tumorigenesis depending on context, with c-Jun often contributing to proliferation and survival signals. It is studied as a potential target for therapeutic intervention in cancers and inflammatory diseases. Model organisms lacking c-Jun display impaired development and stress responses, underscoring its essential physiological roles.