Estrogen receptor-mediated proliferation of breast cancer cells is facilitated through expression of multiple primary target genes, products of which induce the secondary response to stimulation. To differentiate between the primary and secondary target genes of estrogen receptor signaling, we measured dynamics of protein expression induced by estradiol in MCF-7 breast cancer cells. Measurement of the global proteomic effects of estradiol by SILAC resulted in identification of 104 estradiol-regulated proteins, with only 41 corresponding genes having estrogen response elements (EREs). Selected reaction monitoring assays were used to validate 32 proteins and measure the dynamics of their expression within 72 hours upon estradiol stimulation and in the presence of 4-hydroxytamoxifen, thus confirming estrogen receptor-mediated signaling. Dynamics of protein expression revealed immediate early response proteins including TFF1 and CDK1 and delayed response proteins including CDK2 and NAB2. Presence or absence of EREs in the corresponding genes indicated early or delayed expression of proteins identified by SILAC. Finally, we measured accurate dynamics of estradiol-induced protein expression in the sub-network of primary and secondary targets of estrogen receptor. Interestingly, since NAB2 protein is also a repressor of EGR3-induced transcription, siRNA-mediated silencing of NAB2 resulted in the over-expression of some EGR3-induced proteins, such as ITGA2. To conclude, quantitative proteomics revealed secondary targets of estrogen receptor signaling potentially overlooked by genome-wide profiling of EREs and provided dynamics of protein expression in the network of transcription factors with a negative feedback loop.