CRMP-1 (collapsing response mediator protein-1) is an invasion suppressor that can predict the outcome and metastasis of lung cancer patients. This study we investigate the regulatory mechanism of CRMP-1 expression for possible therapeutic implication. We found that the COX-2 inhibitor, NS-398, can dose-dependently up-regulate CRMP1 expression and suppress cancer cell invasion. To dissect the mechanism of COX-2 inhibitor on CRMP1 regulation, the basal transcriptional regulation region of CRMP-1 gene, located between nt -99 to -180 and contained two putative Sp1 and two C/EBPα sites, was identified by reporter assay and employed to further investigation. Site-directed mutagenesis and deletion analysis revealed that two C/EBPα sites, from nt -128 to -135 and -105 to -114, are the most important positive regulatory element. This C/EBPα binding element is overlapped with the SP1 sites (C/EBPα-SP1 element). Gel-shift and antibody super-shift assays demonstrated that Sp1 proteins also bind to this C/EBPα-SP1 element. The SP1 and C/EBPα compete with each other in binding to this complex element. Over-expression of Sp1 could suppress the CRMP-1 promoter activity and protein level; on the contrary, over-expressing C/EBPα increase the CRMP-1 promoter activity and protein expression level. We further confirmed that COX-2 inhibitor up-regulates the CRMP-1 promoter activity by inhibiting the Sp1 proteins from binding to the SP1 sites. We concluded that C/EBPαand SP1 counter-regulate CRMP-1 promoter activity. The COX-2 inhibitor can disrupt Sp1-DNA complex and enhance the DNA binding activity of C/EBPα, further lead to increase CRMP-1 expression and inhibit cancer cell invasion.
[Proc Amer Assoc Cancer Res, Volume 47, 2006]