The
tumor invasive phenotype driven by
seprase expression/activity has been widely examined in an array of malignant
tumor cell types; however, very little is known about the transcriptional regulation of this critical
protease.
Seprase (also named fibroblast activation
protein-α,
antiplasmin-cleaving
enzyme, and dipeptidyl prolyl
peptidase 5) is expressed at high levels by stromal fibroblast, endothelial, and
tumor cells in a variety of invasive
tumors but is undetectable in the majority of normal adult tissues. To examine the transcriptional regulation of the gene, we cloned the
human seprase promoter and demonstrated that endogenous
seprase expression and exogenous
seprase promoter activity are high in invasive
melanoma cells but not in non-invasive
melanoma cells/primary melanocytes. In addition, we identified a crucial TGF-β-responsive cis-regulatory
element in the proximal
seprase promoter region that enabled robust transcriptional activation of the gene. Treatment of metastatic but not normal/non-invasive cells with TGF-β1 caused a rapid and profound up-regulation of endogenous
seprase mRNA, which coincided with an abolishment of the negative regulator c-Ski, and an increase in binding of Smad3/4 to the
seprase promoter in vivo. Blocking TGF-β signaling in invasive
melanoma cells through overexpression of c-Ski, chemically using
SB-431542, or with a
neutralizing antibody against TGF-β significantly reduced
seprase mRNA levels. Strikingly, RNAi of
seprase in invasive cells greatly diminished their invasive potential in vitro as did blocking TGF-β signaling using
SB-431542. Altogether, we found that
seprase is transcriptionally up-regulated in invasive
melanoma cells via the canonical TGF-β signaling pathway, supporting the roles of both TGF-β and
seprase in
tumor invasion and
metastasis.