CDKN1B and cancer: Although this pathway has been widely demonstrated and seems to play a pivotal role in the control of p27 protein stability in both normal and cancer cell, at least two Skp2-independent pathways have been proved to induce p27 degradation during G1: the KPC1-KPC2 ubiquitin-ligases [14] and the activation of the Wnt-Cul4A pathway [15].