Background: Fascin is an actin-bundling protein that is absent from most normal epithelia yet is upregulated in multiple forms of human carcinoma, where its expression correlates clinically with a poor prognosis. How fascin-1 transcription is activated in carcinoma cells is largely unknown, although the hypothesis of regulation by beta-catenin signaling has received attention. The question is important because of the clinical significance of fascin expression in human carcinomas.
Methodology/principal findings: Through comparative genomics we made an unbiased analysis of the DNA sequence of the fascin-1 promoter region from six mammalian species. We identified two regions in which highly conserved motifs are concentrated. Luciferase promoter reporter assays for the human fascin-1 promoter were carried out in fascin-positive and -negative human breast and colon carcinoma cells, and in human dermal fibroblasts that are constitutively fascin-positive. In all fascin-positive cells, the region -219/+114 that contains multiple highly conserved motifs had strong transcriptional activity. The region -2953/-1582 appeared to contain repressor activity. By examining the effects of single or multiple point mutations of conserved motifs within the -219/+114 region on transcriptional reporter activity, we identified for the first time that the conserved CREB and AhR binding motifs are major determinants of transcriptional activity in human colon carcinoma cells. Chromatin immunoprecipitations for CREB, AhR or beta-catenin from extracts from fascin-positive or -negative human colon carcinoma cells identified that CREB and AhR specifically associate with the -219/+114 region of the FSCN1 promoter in fascin-positive colon carcinoma cells. An association of beta-catenin was not specific to fascin-positive cells.
Conclusion: Upregulation of fascin-1 in aggressive human carcinomas appears to have a multi-factorial basis. The data identify novel roles for CREB and AhR as major, specific regulators of FSCN-1 transcription in human carcinoma cells but do not support the hypothesis that beta-catenin signaling has a central role.