CUTL1–a modulator of tumor cell invasion and target of TGF-beta which is highly expressed in colon cancer

Abstract

CUTL1, also known as CDP/cux, is an evolutionary conserved homeodomain transcription factor which plays essential roles in development and cell cycle progression. However, little is known about the transcriptional targets of CUTL1 and its role in tumorigenesis and tumor progression. To elucidate the transcriptional program induced by CUTL1, we employed genome-wide expression profiling using Affymetrix microarrays comparing NIH3T3 cells with stable suppression of CUTL1 by shRNA technology and NIH3T3 cells with endogenous CUTL1 expression. These data revealed that CUTL1 activates a complex transcriptional program with upregulation of numerous genes involved in cell motility, invasion and modulation of extracellular matrix. Many of these putative target genes could be subsequently confirmed on mRNA and protein level as well as on promoter level. Using various approaches such as wound healing, two-chamber migration and invasion assays as well as 24-hrs video time lapse microscopy with or without knockdown of CUTL1 expression by siRNA, we could confirm that CUTL1 activity is associated with increased migration and invasiveness in several tumor cell systems of epithelial and non-epithelial origin. Furthermore, we show that CUTL1 is a transcriptional target of TGF-beta signaling and acts as an important mediator of the pro-migratory and pro-invasive effects induced by TGF-beta, both via Smad4-dependent and p38MAPK-dependent pathways. In contrast, protein kinase A, which is known to inhibit tumor progression in several tumor types, was shown to directly phosphorylate CUTL1, thereby inhibiting its transcriptional activity. The pathophysiological significance of the pro-invasive and tumor-promoting role of CUTL1 was confirmed by the fact that it was found to be strongly expressed and to correlate with tumor grade in a variety of tumor cells and tissues, among them colon cancer tissues.