1. ¹Institute of Biotechnology in Medicine, National Yang-Ming University, Taipei, Taiwan
2. ²Division of Internal Medicine and Cancer Center, Taipei Veterans General Hospital, Taipei, Taiwan

Correspondence: Dr EIT Chen, Institute of Biotechnology in Medicine, National Yang-Ming University, Lee-Lun Street, Section 2, 112, Taipei, Taiwan. E-mail: chenit@ym.edu.tw

³These authors contributed equally to this work.

Received 15 February 2005; Revised 2 November 2005; Accepted 2 November 2005; Published online 5 December 2005.

Abstract

The adenovirus E1A protein has been shown to be involved in the potentiation of apoptosis induced by chemotherapeutic agents, yet the molecular events of E1A-mediated apoptosis are not very clear. A recent report has suggested that deamidation of the Bcl-X_L protein inhibits its antiapoptotic ability and leads to apoptosis induced by alkylating agents in Rb-deficient tumor cells. Since Rb is known to interact with E1A, which interrupts Rb's normal function, we examined Bcl-X_L deamidation and cell death induced by cisplatin in E1A transfectants. We found that the E1A transfectants became sensitive to cisplatin-induced apoptosis compared to the parental cells, SKOV3.ip1. Our data show that cisplatin treatment induced the modification of Bcl-X_L in the E1A transfectants in dosage and time-dependent manner. Furthermore, phosphatase treatment had no effect on the level of Bcl-X_L modification, whereas alkaline lysis buffer appeared to induce the same modification of Bcl-X_L. Ectopic expression of the deamidated forms of Bcl- X_L in SKOV3.ip1 cells revealed that the modification to the Bcl- X_L protein molecules was deamidation. Expression of the E1A mutant (dl1108) which contains deletion at CR2 domain suppressed Bcl-X_L deamidation and apoptosis induced by cisplatin. We also found that expression of the nondeamidated Bcl-X_L protected E1A transfectants from apoptosis. These findings suggest that Bcl-X_L deamidation contributes to E1A-mediated cisplatin sensitization in SKOV3.ip1 cells.