MDM2 promotes cancer cell survival through regulating the expression of HIF-1α and pVHL in retinoblastoma

Hypoxia is an important tumor feature and hypoxia-inducible factor 1 (HIF-1) is a master regulator of cell response to hypoxia. Mouse double minute 2 homolog (MDM2) promotes cancer cell survival in retinoblastoma (RB), with the underlying mechanism remaining elusive. In this study, we investigated the role of MDM2 and its relation to HIF-1 alpha in RB. Expression analysis on primary human RB samples showed that MDM2 expression was positively correlated with that of HIF-1 alpha while negatively correlated with von Hippel-Lindau protein (pVHL), the regulator of HIF-1 alpha. In agreement, RB cells with MDM2 overexpression showed increased expression of HIF-1 alpha and decreased expression of pVHL, while cells with MDM2 siRNA knockdown or MDM2-specific inhibitor showed the opposite effect under hypoxia. Further immuno-precipitation analysis revealed that MDM2 could directly interact with pVHL and promotes its ubiquitination and degradation, which consequently led to the increase of HIF-1 alpha. Inhibition of MDM2 and/or HIF-1 alpha with specific inhibitors induced RB cell death and decreased the stem cell properties of primary RB cells. Taken together, our study has shown that MDM2 promotes RB survival through regulating the expression of pVHL and HIF-1 alpha, and targeting MDM2 and/or HIF-1 alpha represents a potential effective approach for RB treatment.