MDM2

Murine double minute 2 (MDM2) is an E3 ubiquitin ligase that functions as a primary negative regulator of the tumor suppressor p53^[1][2]. Mechanistically, MDM2 ubiquitinates p53, targeting it for proteasomal degradation, while also regulating additional transcription factors and post-transcriptional processes independently of p53^[1][2][6]. MDM2 interacts with its homolog MDM4 (MDMX) through RING domain heterodimers, modulating protein stability and p53 activity^[1][7]. Compared with MDM4, MDM2 possesses intrinsic E3 ligase activity and can degrade p53 even in the absence of MDM4, whereas MDM4 stabilizes the heterodimer complex without ubiquitin ligase function^[1][5][7]. Dysregulation of MDM2 contributes to oncogenesis across multiple malignancies, including leukemia, neuroblastoma, breast cancer, and Theileria parva-induced lymphoproliferative disorders^{[4][7][8][13][16]}. In experimental models, inhibition of MDM2 with small molecules such as RG7112, MI-63, CGM097, or XR-2 stabilizes p53, induces apoptosis, and can synergize with other pathway modulators to enhance anti-tumor activity^{[4][9][10][11][16]}. Recent strategies exploit protein-protein interfaces, such as the MDM2-CK1α interaction, to induce targeted protein modifications and p53 activation independently of p53 status, providing tools for mechanistic studies and therapeutic design^[14][17]. MDM2 inhibitors and dual MDM2/MDM4-targeting agents demonstrate isoform-specific effects, highlighting the importance of distinguishing functional contributions of MDM2 versus MDM4 in both experimental and therapeutic contexts^[12][3][15].