FOXO1 and pachyonychia congenita: Skp2 promotes ubiquitin-mediated proteolysis of its substrates, including p21, p27, p57, E-cadherin, and Foxo1 (forkhead box O1), leading to its oncogenic role in tumorigenesis.7, 8, 9 We previously found that ATO inhibited PC cell growth and migration through downregulation of Skp2 expression.10