| Summary: | 碩士 === 淡江大學 === 化學學系碩士班 === 95 === The Epidermal Growth Factor Receptor (EGFR) and cyclin D1 are frequently amplified, overexpressed, or mutated in many cancers, including skin. We have previously demonstrated that the locally cultivated Ganoderma tsugae (G. tsugae, Lingzhi) extract possessing anti-cancer and anti-angiogenic properties in vitro and in vivo. The aim of the present work was to investigate the role of G. tsugae extracts in anti-cancer properties of EGFR-overexpressing human epidermoid carcinoma A431 cells. Using MTT assay, we demonstrated that G. tsugae extracts could inhibit the growth of A431 cells in a dose- and time-dependent manner. Western blotting analysis was used to investigate the mechanism of these effects. We demonstrated here a dose- and time-dependent down-regulation of expression of EGFR, cyclin D1 and CDK4 by G. tsugae extracts those correlate with the decrease in the proliferation of A431 cells. We also found that G. tsugae extracts-induced down-regulation of cyclin D1 was reversed by proteasome inhibitor, MG132, suggesting the role of ubiquitin-dependent proteasomal pathway. Furthermore, G. tsugae extracts treatment could cause the de-phosphorylation of constitutively active AKT and GSK3-beta. These finding suggest that G. tsugae extracts induces cell cycle arrest through proteasomal degration of cyclin D1 in EGFR-overexpressing human epidermoid carcinoma A431 cells might via the phosphatidylinositol 3-kinase/Akt-dependent pathway. Additionally, G. tsugae extracts could dramatically induce the expression of p21 while significantly inhibit the expression of the G1 phase cell cycle regulatory gene such as cyclin D1 and could suppress the expression of CDK4 protein. Taken together, our results suggest that proteasome-mediated down-regulation of cyclin D1 and up-regulation of CDK inhibitor might contribute to the antiproliferative effect of G. tsugae extracts against EGFR-overexpressing human epidermoid carcinoma.
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