ted transcription factor, Smad4. Our data revealed that MMP7 e pression levels and activity were significantly decreased in the Smad4 knockdown OSCC cells. Additionally, we used immunoprecipitation techniques to confirm the occurrence of interactions between SIRT1, Smad4, and MMP7 in OSCC cells. thenthereby Interestingly, SIRT1 was shown to directly interact with Smad4 in vivo, but did not interact with MMP7 protein. We also showed that overe pression of SIRT1 repressed TGF B induced MMP7 e pression by deace tylating Smad4, which becomes hypere pressed and hyperacetylated under conditions of TGF B stimulation. SIRT1 was shown to affect Smad4 transcriptional activity by deacetylation, and inhibition of Smad4 function repressed TGF B induced EMT. These observations clearly show that SIRT1 might influence MMP7 e pression, secretion, and activity.
and subsequently, cell migration, invasion, and metastasis through Smad4 deacetylation. Furthermore, we also showed that SIRT1 overe pressing cells inhibited MMP7 secretion and increased E cadherin accumulation, leading to suppres sion of cellular invasion and migration. Our results indicate that MMPs can mediate both the EMT process and cell metastasis, as well as cause nuclear translocation of B catenin by proteolytic cleavage and release of E cadherin from the cell surface. It is therefore inter esting to speculate that SIRT1 maybe lead to repression of a second pathway involved in EMT, such as the Wnt signaling pathway.
Conclusions In conclusion, our study identified SIRT1 as a novel metastatic suppressor which acts through deacetylation of TGF B activated transcription factor Smad4 to suppress the effect of TGF B signaling on MMP7 transcription, leading to reduced migration and metastasis of OSCC cells. SIRT1 shows potential for serving as a predictor and biomarker for metastasis, and up regulation of SIRT1 is a potentially useful therapeutic strategy for inhibiting the metastasis of oral cancers. Methods Cell culture and reagents The HOK cells used in this study were cultured in oral keratinocyte growth medium in a 37 C incubator filled with 5% CO2, and were routinely passaged at 90% confluence. Five human OSCC cell lines, OC3, SCC4, and SCC 25 ] were used in this study. HSC 3 and OC3 cells were cultured in Dulbeccos modified Eagles medium contain ing 2 mM glutamine.
OECM 1 cells were maintained in RPMI 1640 medium, while SCC4 and SCC25 cells were cultured in DMEM F12 medium. Each culture medium was supplemented with 10% fetal bovine serum and 100 units mL each of penicillin and streptomycin. All OSCC cells were maintained at 37 C in a humidified atmosphere of 5% CO2. The SIRT1 agonist and antagonists were purchased from Sigma Aldrich. Plasmid construction and transient transfection The conditions for Drug_discovery PCR were as follows denaturing for 30 sec at 94 C, annealing for 30 sec at 62 C and elongation for 1 minute at 72 C for 35 cycles. The full length of SIRT1 gene was subcloned into the etc constitutive mammalian e pressi