Inhibition of tumor growth and metastasis of human melanoma by intracellular anti-ATF-1 single chain Fv fragment

Activating transcription factor-1 (ATF-1) and cAMP-responsive element (CRE) -binding protein (CREB) have been implicated in cAMP and Ca2+-induced trans criptional activation. The expression of the transcription factors CREB and ATF-1 is upregulated in metastatic melanoma cells. However, how overexpres sion of ATF-1/CREB contributes to the acquisition of the metastatic phenoty pe remains unclear. Here, the effect of disrupting ATF-1 activity was inves tigated using intracellular expression of an inhibitory anti-ATF-1 single c hain antibody fragment (ScFv), Intracellular expression of ScFv anti-ATF-1 in MeWo melanoma cells caused significant reduction in CRE-dependent promot er activation. In addition, expression of ScFv anti-ATF-1 in melanoma cells suppressed their tumorigenicity and metastatic potential in nude mice. ScF v anti-ATF-1 rendered the melanoma cells susceptible to thapsigargin-induce d apoptosis in vitro and caused massive apoptosis in tumors transplanted su bcutaneously into nude mice, suggesting that ATF-1 and its associated prote ins act as survival factor for human melanoma cells. This is the first repo rt to demonstrate the potential of ScFv anti-ATF-1 as an inhibitor of tumor growth and metastasis of solid tumor in vivo.