PIAS3 and breast cancer: Remarkably, expression of the SUMO E3 ligase inactive PIAS3CS, in which the RING finger Cysteine 299 is converted to serine, promoted the invasive growth of breast cancer cell-derived organoids even in the absence of TGFβ (Figure 4A–4C) phenocopying the effect of PIAS3 knockdown (Figure 3C, 3D).