SSAT Inhibits The Proliferation, Migration And Invasion Of Colorectal Carcinoma Cell Via AKT/GSK-3β/β-catenin Signaling Pathway

Background : Colorectal cancer is a common malignant tumor in digestive system, which has a high morbidity and mortality. Understanding the molecular mechanism of tumorigenesis, progression and metastasis of colorectal carcinoma is the first priority for advancing the therapeutic pattern. During the development of cancer therapy, polyamines were considered as efficacious targets for its disturb in various cancers. SSAT, Spermidine/spermine N1-acetyltransferase, is a rate-limiting enzyme in the catabolism of polyamines in eukaryotic cells. The depletion of polyamines by catabolic enzyme SSAT has been demonstrated effects a series of progression in tumor genesis and metastasis in colorectal cancer. However,the precise molecular mechanism of polyamine contents in the role of anticancer remains unclear.Objective : Here, we will investigate the potential role and molecular mechanism of SSAT on the proliferation, migration and invasion of colorectal cancer cell.Methods:Western blot analysis was used to examine the protein expression of SSAT in colorectal cancer cell HCT 116 and HT-29. HPLC analysis detected the level of cellular polyamines in the tumor cell with gain- or loss-of-function of SSAT. Both colony formation assay and cell growth curve analysis were used to detect the cellular proliferation. Additionally, wound healing and Transwell analysis without Matrigel investigated the cellular migration capability. The invasive activity of tumor cells was also investigated by Transwell analysis with Matrigel. Western blot detected the protein expression of AKT, p-GSK-3β,β-catenin, E-cadherin and N-cadherin, which are key roles in AKT signaling and Wnt signaling pathway.Results:1. HPLC analysis showed the level of cellular polyamines was dramatically changed following the gainand loss-of-function of protein SSAT.2. Both colony formation assay and cell growth curve analysis demonstrated up-regulate of SSAT attenuated the cell proliferation, while knockdown of SSAT promoted it.3. Wound healing and Transwell analysis with or without Matrigel indicated that the depletion of polyamines by over expressing SSAT suppressed the migration and invasive activity of tumor cells,whereas SSAT down-regulation promoted it.4. Subsequent investigations revealed that down- or up-regulation of SSAT was accompanied with changes of membrane β-catenin expression as well as AKT and GSK-3β activities.5. After treatment with exogenous polyamines, intracellular polyamine content of HCT 116-SSAT raised again and the protein expression of AKT and p-GSK-3β was also reversed.6. Upon treatment with GSK3β inhibitor Li Cl, the effect of SSAT on invasion was significantly raised compared with HCT 116-SSAT cells.What’s more, the levels of β-catenin was also increased.Conclusions:These results suggest that SSAT is an important regulator of the AKT/β-catenin signaling to reduce the proliferation, invasion and migration of colorectal cancer cells.