STAT5A and breast cancer: Using lysis buffer conditions that included N-ethylmaleimide, which blocks the action of de-SUMOylating enzymes [33], we confirmed the presence of these bands in human breast cancer cells, demonstrating that levels of 95 kDa phospho-STAT5 increased modestly, but significantly, in MDA-MB-231 SH-4-54-resistant clones while decreasing in T47D SH-4-54 resistant clones relative to their respective wild-type counterparts (Fig 6C).