Effects of tamoxifen, 4-hydroxytamoxifen, and deficiency of D -(+)-glucose, L -leucine, L -methionine or L -cysteine on the phosphorylation of S6K1 in MDA-MB-231 cells. (a and e) Western immunoblot analysis of the effects of D-(+)-glucose deficiency, DMSO, tamoxifen and 4-hydroxytamoxifen on the expression of total S6K1 and (b and e) phosphorylated S6K1. (c and e) Westerm immunoblot analysis of the effects of the deficiency of L-leucine, L-methionine or L-cysteine on the expression of total S6K1 and (d and e) phosphorylated S6k1. All assays were performed in triplicates and repeated three times. (f) Correlation between the degree of expression of p27 protein and the degree of down-regulation of phosphorylated S6k1.