Abstract: Objective: To investigate the effect of interleukin-4(IL-4) and estradiol on the biological behavior of breast cancer 4T1 cells of the mice, and to elucidate its mechanism. Methods: The 4T1 cells were cultured in vitro and added with different concentrations (0, 12.5, 25.0, 50.0 and 100.0μg·L^-1) of IL-4 or estradiol (0, 6.25, 12.50, 25.00 and 50.00 nmol·L^-1).The proliferation rate of the breast cancer 4T1 cells was measured by MTT method after treated for 72 h.The breast cancer 4T1 cells were divided into control group (without any treatment), IL-4 group (treated with 50.0μg·L^-1IL-4), estradiol group (treated with 12.50 nmol·L^-1 estradiol) and combination group (treated with 50.0μg·L ^-1 IL-4+ 12.50 nmol·L^-1 estradiol). MTT method was used to detect the proliferation rates of the breast cancer 4T1 cells in various groups, and flow cytometry was used to detect the percentages of the breast cancer 4T1 cells in different cell cycles in various groups,and Western blotting method was used to detect the expression levels of STAT6, p-STAT6, ERα, Erk, p-Erk, P70S6K, p-P70S6K, S6,and p-S6 in the breast cancer 4T1 cells in various groups. Results: Compared with 0μg·L^-1 IL-4 group, the proliferation rates of the breast cancer 4T1 cells in 25.0, 50.0 and 100.0μg·L^-1 IL-4 groups were increased (P<0.05);compared with 0 nmol·L^-1 estradiol groups, the proliferation rates of the breast cancer 4T1 cells in 12.50, 25.00 and 50.00 nmol·L^-1 estradiol groups were increased (P<0.05).Compared with control group, the proliferation rate of the breast cancer 4T1 cells in IL-4 group was increased (P<0.05); compared with control group, the proliferation rate of the breast cancer 4T1 cells in estradiol group was increased (P<0.05); compared with IL-4 group or estradiol group, the proliferation rate of the breast cancer 4T1 cells in combination group was increased (P<0.05).Compared with control group, the percentages of the breast cancer 4T1 cells at S phase and G₂/M phase in IL-4 group were increased (P<0.05),and the percentage of the breast cancer 4T1 cells at G₀ and G₁ phases were decreased(P<0.05); compared with control group, the percentage of the breast cancer 4T1 cells at S phase in estradiol group was increased(P<0.05),and the percentages of the breast cancer 4T1 cells at G₀ and G₁ phases were decreased (P<0.05).Compared with control group, the expression levels of ERα, p-Erk, p-P70S6K, and p-S6 in the breast cancer 4T1 cells in IL-4 group were increased(P<0.05), while the expression levels of p-STAT6, ERα, p-Erk, p-P70S6K, S6,and p-S6 in the breast cancer 4T1 cells in estradiol group were increased (P<0.05); the expression levels of STAT6, p-STAT6, ERα, p-ERK, p-P70S6K, and p-S6, in the breast cancer 4T1 cells in combination group were increased (P<0.05). Conclusion: The combination of IL-4 and estradiol can increase the expressions of IL-4 receptor(IL-4R) and estrogen receptor (ER),and enhance the activation of Erk1, p70S6K kinase and phosphorylation of downstream S6 protein in the breast cancer 4T1 cells.

Key words: interleukin-4, estrogen receptor, breast cancer 4T1 cells, macrophages, tumor microenvironment, synergistic effect