FOS Like Antigen 1 (FOSL1)

The Fos gene family consists of 4 members: FOS, FOSB, FOSL1, and FOSL2. These genes encode leucine zipper proteins that can dimerize with proteins of the JUN family, thereby forming the transcription factor complex AP-1.

Structure-function analysis demonstrated that the major carboxy-terminal transactivation domains of Fos and FosB are dispensable and that Fosl1, which lacks transactivation domains, has the highest rescue activity. Moreover, a transgene expressing Fosl1 rescued the osteopetrosis of Fos mutant mice in vivo. The osteoclast differentiation factor Rankl induced transcription of Fosl1 in a Fos-dependent manner, thereby establishing a link between Rank signaling and the expression of Ap1 proteins in osteoclast differentiation.