Induction of early growth response-1 gene expression by calmodulin antagonist trifluoperazine through the activation of Elk-1 in human fibrosarcoma HT1080 cells

The early growth response gene-1 (Egr-1) is a transcription factor that pla ys an important role in cell growth and differentiation. It has been known that Egr-1 expression is down-regulated in many types of tumor tissues, inc luding human fibrosarcoma HT1080 cells, and introduction of the Egr-1 gene into HT1080 cells inhibits cell growth and tumorigenic potential. Trifluope razine (TFP), a phenothiazine class calmodulin antagonist, is known to inhi bit DNA synthesis and cell proliferation and potentially important in antit umor activities. To understand the regulatory mechanism of Egr-1, we invest igated the effect of TFP on expression of Egr-1 in HT1080 cells. Herein, we report that Egr-1 expression was increased by TFP in synergy with serum at the transcriptional level. Both the Ca2+/calmodulin-dependent protein kina se II inhibitor KN62 and the calcineurin inhibitor cyclosporin A enhanced T FP-dependent increase of Egr-1, suggesting that the Ca2+/calmodulindependen t pathway plays a role in regulation of Egr-1 expression in HT1080 cells. T he TFP-stimulated increase of the Egr-1 protein was preferentially inhibite d by the MEK-specific inhibitor PD98059. In addition, activation of human E gr-1 promoter and the transcriptional activation of the ternary complex fac tor Elk-l induced by TFP were inhibited both by pretreatment of PD98059 and by expression of the dominant-negative RasN17. These results indicate that the Ras/MEK/Erk/Elk-1 pathway is necessary for TFP-induced Egr-1 expressio n. We propose that the calmodulin antagonist TFP stimulates Egr-1 gene expr ession by modulating Ras/MEK/Erk and activation of the Elk-1 pathway in hum an fibrosarcoma HT1080 cells.