COL4A1 and cancer: Included among the more robust Steiner nodes (node size correlates with robustness to perturbation) are proteins that have been linked to EMT signaling in cancer, such as PIAS1, a SUMO E3 ligase that is repressed by TGF-β to prevent EMT suppression [56], and COL4A1, which has also been linked to TGF-β stimulation [57].