Immunohistochemistry analysis showed a significant increase of p27+FOXP3+ cells (Fig. 5h) in YUMMER1.7 melanoma tumors grown in Siah2−/− compared to WT mice, confirming increases in levels of p27 protein in the Siah2−/−-derived intratumoral Treg cell population and strongly suggesting that Siah2 controls Treg proliferation via p27. The gene discussed is FOXP3; the disease is melanoma.