NECTIN4 and neoplasm: To obtain further insights into the mechanisms underlying the inhibition of cell proliferation in NECTIN4 siRNA-transfected cells, the phosphorylation status of ERK and Akt (a downstream molecule of phosphatidylinositol 3-kinase: PI3K signaling)—both known to regulate tumor cell proliferation [37,38,39,40,41,42]—was assessed.