CDK4 and neoplasm: Western blot analysis of xenograft tumor issues showed that HBO1, cyclin-related protein CDK4, and anti-apoptotic protein BCL2 were decreased, but P21 and cleaved PARP protein expression were increased in HBO1-sh1 NALM-6 xenograft tissues (Fig. 7F), indicating the arrest of the cell cycle and the activation of apoptosis.