Abstract: Objective: To investigate the effects of lysine acetyltransferase (Kat5) on the proliferation and apoptosis of the thyroid papillary carcinoma cells and the role of phosphatidylinositol 3-kinase (PI3K)/serine/threonine kinase (AKT) signaling pathway,and to elucidate the possible mechanism of Kat5 in the proliferation and apoptosis of thyroid papillarycarcinoma cells. Methods: RT-PCR and Western blotting methods were used to determine the expression levels of Kat5 mRNA and protein in the thyroid papillary carcinoma BHP10-3, TPC-1, K1 cells and thyroid epithelial Nthy-ori3-1 cells.The thyroid papillary carcinoma TPC-1 cells were divided into blank control group, negative control group and silencing Kat5 group (si-Kat5 group).The cells in blank control group were not transfected,the cells in negative control group were transfected with negative control siRNA,and the cells in si-Kat5 group were transfected with Kat5 siRNA.The expression levels of Kat5 mRNA and protein in the thyroid papillary carcinoma TPC-1 cells in various groups were detected by RT-PCR and Western blotting methods.The proliferation activities of the TPC-1 cells in various groups were measured by CCK-8 method,the colony formation assay was used to measure the clone formation rates of the TPC-1 cells in various groups,the apoptotic rates of the TPC-1 cells in various groups were detected by flow cytometry,and the expression levels of cyclin-dependent kinase 2(CDK2), P21, P53, cleaved caspase-3, PI3K, phosphorylated PI3K (p-PI3K), AKT, and phosphorylated AKT(p-AKT) protein in the TPC-1 cells in various groups were detected by Western blotting method. Results: The expression levels of Kat5 mRNA and protein in the thyroid papillary carcinoma BHP10-3, TPC-1 and K1 cells were higher than those in thyroid epithelial Nthy-ori3-1 cells (P<0.05).The differences in the Kat5 mRNA and protein expression levels,the proliferation activities,the clone formation rates,the apoptotic rates and the expression levels of CDK2, P21, P53, cleaved caspase-3, PI3K, p-PI3K, AKT and p-AKT proteins in the TPC-1 cells between various groups were statistically significant(P<0.05).Compared with blank control group and negative control group, the expression levels of Kat5 mRNA and protein in the TPC-1 cells in si-Kat5 group were decreased(P<0.05), the proliferation activity was decreased(P<0.05),the colony formation rate was decreased(P<0.05),the apoptotic rate was increased(P<0.05), the expression levels of CDK2, p-PI3K and p-AKT proteins were decreased(P<0.05), and the expression levels of P21, P53 and cleaved caspase-3 proteins were increased(P<0.05). Conclusion: The expression levels of Kat5 mRNA and protein in the thyroid papillary carcinoma cells are increased. Silencing Kat5 gene can inhibit the proliferation of the thyroid papillary carcinoma cells and promote their apoptosis,and tis mechanism may be related to the inhibition of PI3K/AKT signaling pathway.

Key words: lysine acetyltransferase, thyroid papillary carcinoma, cell proliferation, apoptosis, phosphatidylinositol 3-kinase/serine/threonine kinase