p16 inhibits matrix metalloproteinase-2 expression via suppression of Sp1-mediated gene transcription

Previous studies demonstrate that p16, a cyclin-dependent kinase inhibitor and a tumor suppressor, may inhibit matrix metalloproteinase-2 (MMP-2) expression inhuman cancer cells to suppress tumor invasion and metastasis. However, the detailed mechanism is still unclear. Our results show that p16 inhibits MMP-2 expression via transcriptional repression. Promoter deletion and mutation analysis indicates that pi 6 acts through the Sp1 transcription factor-binding site located between -72 and -64 bp region from the transcriptional start site of the human MMP-2 promoter to repress gene expression. DNA affinity precipitation assay (DAPA) and chromatin immuno-precipitation (CHIP) assay demonstrate that Sp1 proteins constitutively bind to this consensus sequence in vitro and in vivo. p16 attenuates Sp1 binding to the MMP-2 promoter to suppress gene transcription and overexpression of Sp1 may counteract p16-induced downregulation of MMP-2. CyclinA/CDK complex may directly phosphorylate Sp1 and enhance its DNA-binding activity. Thus, we investigated the effect of p16 on the interaction between cyclin A and Sp1. Our results indicate that p16 induces downregulation of cyclin A and CDK2, reduces the interaction between cyclin A and Sp1, and attenuates phosphorylation of Sp1. Ectoexpression of cyclin A counteracts p16-mdeiated inhibition of DNA binding of Slot and activates MMP-2 promoter activity and mRNA expression. Collectively, our results suggest that p16 suppresses MMP-2 by blocking Sp1-mediated gene transcription.