Interruption of NFkappaB-STAT1 signaling mediates EGF-induced cell-cycle arrest.
It is known that EGF induces the cell-cycle arrest in A431 cells that possess high numbers of EGF receptors and it was previously suggested that p21/WAF1 protein was a major effector molecule of the EGF-mediated cell-cycle arrest of A431 cells. Here, we further investigate this phenomenon using the decoy double-strand oligonucleotides for STAT-binding sequence (STAT decoy) and IkappaB, an inhibitor of the nuclear factor kappa B (NFkappaB). Addition of STAT decoy restored EGF-induced A431 cell-growth arrest. Interestingly, infection of adenovirus vectors to express IkappaB (AxIkappaBalphaDeltaN) as the inhibitor of NFkappaB also reversed the A431 cell-growth inhibition. The individual treatment of two inhibitors partially inhibited the WAF1 gene expression, whereas simultaneous treatment of two inhibitors exhibited more efficient inhibition. These observations suggest the activation of NFkappaB via IkappaB degradation and STAT1 via specific receptor kinase activity synergistically induce WAF1 gene expression in A431 cells. Thus, NFkappaB and STAT1 pathways mutually interact to play an important role in the EGF-induced intracellular reaction.