SNAI1 and breast cancer: Importantly, knockdown of Slug in MDA-231 and MDA-157 breast cancer cell lines that express high levels of Slug, by either transient transfection with siRNAs or stable expression of specific shRNAs, provided results similar to the knockdown of Snail: a profound increase in 4E-BP1 expression at both the mRNA and protein levels (Supplementary Fig. 6a, e–j).