Involvement of the CDK2-E2F1 pathway in cisplatin cytotoxicity in vitro and in vivo.

E2F1 is a key regulator that links cell cycle progression and cell death. E2F1 activity is controlled by Cdk2-cyclin complexes via several mechanisms, such as phosphorylation of retinoblastoma protein (pRb) to release E2F1, direct phosphorylation, and stable physical interaction. We have demonstrated that cisplatin cytotoxicity depends on Cdk2 activity, and Cdk2 inhibition protects kidney cells from cisplatin-induced cell death in vitro and in vivo. Now we show that E2F1 is an important downstream effector of Cdk2 that accumulates in mouse kidneys and in cultured mouse proximal tubular cells (TKPTS) after cisplatin exposure by a Cdk2-dependent mechanism. Direct inhibition of E2F1 by transduction with adenoviruses expressing an E2F1-binding protein (TopBP1) protected TKPTS cells from cisplatin-induced apoptosis, whereas overexpression of E2F1 caused cell death. Moreover, E2F1 knockout mice were markedly protected against cisplatin nephrotoxicity by both functional and histological criteria. Collectively, cisplatin-induced cell death is dependent on Cdk2 activity, which is at least partly through the Cdk2-E2F1 pathway both in vitro and in vivo.