Abstract: 【Abstract】 Objective To investigate the effect of a short hairpin RNA （shRNA） targeting epidermal growth factor receptor （EGFR） combined with sirolimus on proliferation and apoptosis of the human cutaneous squamous cell carcinoma cell line Colo-16, and to explore underlying mechanisms. Methods Cultured Colo-16 cells were divided into 5 groups: normal cell group receiving conventional culture and treatment with phosphate-buffered saline （PBS）, negative control group transfected with a shRNA-NC-expressing plasmid and treated with PBS, sirolimus group receiving conventional culture and sirolimus treatment, EGFR shRNA group transfected with an EGFR shRNA-expressing plasmid and treated with PBS, and combined group transfected with an EGFR shRNA-expressing plasmid and treated with sirolimus. Methyl thiazol tetrazolium （MTT） assay was performed to evaluate cellular proliferative activity in the above groups from 24 to 96 hours, and flow cytometry to detect cell apoptosis after 48-hour treatment. Semiquantitative RT-PCR was conducted to determine the mRNA expression of Bcl-2 and Bax, and Western blot analysis to determine the expression of apoptosis-related proteins cleaved caspase-3, cleaved caspase-9, Bcl-2, Bax, cell proliferation-related proteins phosphorylated mammalian target of rapamycin （p-mTOR）, phosphorylated protein kinase B （p-AKT）, phosphorylated 70-kDa ribosomal protein S6 kinase （p-P70S6k）, and cyclin D1. Comparisons among groups were carried out by using one-way analysis of variance, and multiple comparisons between 2 groups by using Student-Newman-Keuls q test. Results MTT assay showed that the proliferative activity of Colo-16 cells was significantly lower in the sirolimus group, EGFR shRNA group and combined group during 24 - 96 hours than in the normal cell group （all P < 0.05）, and higher in the combined group than in the sirolimus group and EGFR shRNA group at 24 - 96 hours （all P < 0.001）, and there was no significant difference in the cellular proliferative activity at any time points between the normal cell group and negative control group （all P > 0.05）. Flow cytometry showed that the apoptosis rate was significantly higher in the sirolimus group, EGFR shRNA group and combined group （9.52% ± 0.25%, 12.65% ± 0.23%, 19.81% ± 0.31%, respectively） than in the normal cell group （3.33% ± 0.18%, q = 60.07, 78.08, 122.81, respectively, all P < 0.001） and negative control group （3.42% ± 0.19%, q = 59.90, 77.91, 122.64, respectively, all P < 0.001）, and was highest in the combined group. As RT-PCR and Western blot analysis revealed, the sirolimus group, EGFR shRNA group and combined group showed significantly decreased mRNA expression of Bcl-2 and protein expression of cyclin D1, p-AKT, p-mTOR, p-P70S6K and Bcl-2, but significantly increased mRNA expression of Bax and protein expression of cleaved caspase-3, cleaved caspase-9 and Bax compared with the normal cell group（all P < 0.05）. Compared with the sirolimus group and EGFR shRNA group, the combined group showed significantly decreased mRNA expression of Bcl-2 and protein expression of cyclin D1, p-AKT, p-mTOR, p-P70S6K and Bcl-2 （all P < 0.05）, but significantly increased mRNA expression of Bax and protein expression of cleaved caspase-3, cleaved caspase-9 and Bax （all P < 0.01）. Conclusion EGFR shRNA and sirolimus exerted a synergistic effect in inhibiting the proliferation and promoting the apoptosis of Colo-16 cells, which may be related to the inhibition of the phosphoinositide 3-kinase （PI3K）/AKT/mTOR pathway.

Key words: Carcinoma, squamous cell, Receptor, epidermal growth factor, RNA interference, Sirolimus, Cell proliferation, Apoptosis