Controls osteoclast survival and size (By similarity). As a dimer with JUN, activates LIF transcription (By similarity). Activates CEBPB transcription in PGE2-activated osteoblasts (PubMed:15299028). Heterodimer (By similarity). Interacts with the BAF multiprotein chromatin-remodeling complex subunits SMARCB1 and SMARCD1 (By similarity). Interacts with ARID1A and JUN (By similarity). Expressed in the brain cortex. Expressed at night in pineal gland (at protein level). Also expressed in osteoblasts (at protein level). In the pineal gland, exhibits night/day variations with a 4-fold increased expression at night (at protein level). Up-regulation is due to a large degree to the release of norepinephrine from nerve terminals in the pineal gland and cAMP signaling pathway. Nocturnally elevated expression is also observed in the brain cortex. In osteoblasts, up-regulated by PGE2 (at protein level). Belongs to the bZIP family. Fos subfamily.