SKP2 and cancer: Given that SKP2 plays critical roles in mediating the ubiquitin-dependent degradation of some cell-cycle proteins, including p27, p21 and p57 [12,13], and that aberrant SKP2 expression may contribute to the progression and development of a number of malignant tumors in humans, the effects of curcumin on SKP2 and the molecular relationship between these effects and the differential induction of p27 and p21 were further investigated in MCF-7 and MDA-MB-231 cells.