SKP2 and lip and oral cavity carcinoma: Down-regulation of the protein level of Akt, phospho-Akt Ser473, phospho-Akt Thr308, Gsk3β, Skp2, phospho-Rb Ser807/811, phospho-FOXO1 Thr24, phospho-FOXO3a Thr32, and cyclin D1 coupled with the accumulation of p27Kip1 protein likely contribute to the induction of G2/M cell cycle arrest and growth inhibition in TW2.6 oral cancer cells.