SKP2 and breast cancer: It is also reported that Skp2 can be phosphorylated on Ser64 by p38/MAPK, protecting Skp2 from proteasomal degradation by NK3 homeobox 1 (Nkx3-1), finally leading to Oct-4 (Octamer-binding transcription factor) over-expression and contributing to tamoxifen-resistance in MCF-7 breast cancer cells [50].