The AP-1 Site and the cAMP- and Serum Response Elements of the c-fosGene Are Constitutively OccupiedIn Vivo

摘要

ABSTRACTThe c-fosproto-oncogene is inducible by cAMP, phorbol esters, serum, and growth factors. The induction by cAMP is mediated by the conserved cAMP response element (CRE), while induction by phorbol esters, serum, and growth factors requires a distal element called the serum response element (SRE). In addition to these elements, a consensus AP-1 transcription factor binding site is located next to SRE. Upstream regions of the mouse and human c-fosgenes were footprintedin vivoby the ligation-mediated polymerase chain (PCR). Our results show that all three elements are constitutively protected in mouse liver and lung and in cultured human A431 cells. No major change in the protection profile was detected in A431 cells following stimulation with epidermal growth factor or in mice at birth, when c-fosis known to be induced. These results suggest that the inducibleciselements of the c-fosgene are poised, ready to respond immediately to external signals.