Ets-1 and Runx2 Regulate Transcription of a Metastatic Gene, Osteopontin, in Murine Colorectal Cancer Cells*

Abstract

Osteopontin (OPN) is a sialic acid-rich phosphoprotein secreted by a wide variety of cancers. We have shown previously that OPN is necessary for mediating hepatic metastasis in CT26 colorectal cancer cells. Although a variety of stimuli can induce OPN, the molecular mechanisms that regulate OPN gene transcription in colorectal cancer are unknown. We hypothesized that cis- and trans-regulatory elements determine OPN transcription in CT26 cells. OPN transcription was analyzed in CT26 cancer cells and compared with YAMC (young adult mouse colon) epithelial cells. Clonal deletion analysis of OPN promoter-luciferase constructs identified cis-regulatory regions. A specific promoter region, nucleotide (nt) –107 to –174, demonstrated a >8.0-fold increase in luciferase activity in CT26 compared with YAMC. Gel-shift assays sublocalized two cis-regulatory regions, nt –101 to –123 and nt –121 to –145, which specifically bind CT26 nuclear proteins. Competition with unlabeled mutant oligonucleotides revealed that the regions nt –115 to –118 and nt –129 to –134 were essential for protein binding. Subsequent supershift and chromatin immunoprecipitation assays confirmed the corresponding nuclear proteins to be Ets-1 and Runx2. Functional relevance was demonstrated through mutations in the Ets-1 and Runx2 consensus binding sites resulting in >60% decrease in OPN transcription. Ets-1 and Runx2 protein expression in CT26 was ablated using antisense oligonucleotides and resulted in a >7-fold decrease in OPN protein expression. Ets-1 and Runx2 are critical transcriptional regulators of OPN expression in CT26 colorectal cancer cells. Suppression of these transcription factors results in significant down-regulation of the OPN metastasis protein.