FOSL1 and neoplasm: We inhibit tumor cell proliferation by decreasing or blocking the cytoplasmic function of Fra-1 and c-Fos without affecting their nuclear function as AP-1 transcription factors because both deletion mutants examined, lack the AP-1 dimer formation domain (LZ) of the C-terminus of these proteins and the recognition domain for their nuclear translocator system (BD) (36, 37).