“…Indeed, although MDM2 interacts with proteins, fulfilling a variety of cellular functions (p300, pRb, Numb, MTBP (MDM2-binding protein), DNA polymerase ⑀, promyelocytic leukemia protein, Tip60, YY1, insulin-like growth factor 1 receptor, glucocorticoid receptor/estrogen receptor, androgen receptor, hypoxia-inducible factor 1, p73, NF-B, PSD-95, ADP ribosylation factor, E2F1, TATA-binding protein, TAFII250, Sp1, ribosomal L5, TSG 101, Ras-GAP binding proteins), the biological significance of these multiple interactions remains to be explained (for review, see Refs. 15,22). It should be stressed that not all MDM2 client proteins are targeted for proteasome-dependent degradation; hence, not all involvement of MDM2 protein can be explained by its E3 ubiquitin ligase activity (13,15).…”