Induction of endogenous Bcl-xS through the control of Bcl-x pre-mRNA splicing by antisense oligonucleotides

Abstract

Resistance to apoptosis, which plays an important role in tumors that are refractory to chemotherapy, is regulated by the ratio of antiapoptotic to proapoptotic proteins. By manipulating levels of these proteins, cells can become sensitized to undergo apoptosis in response to chemotherapeutic agents. Alternative splicing of the bcl-x gene gives rise to two proteins with antagonistic functions: Bcl-xL, a well-characterized antiapoptotic protein, and Bcl-xS, a proapoptotic protein. We show here that altering the ratio of Bcl-xL to Bcl-xS in the cell using an antisense oligonucleotide permitted cells to be sensitized to undergo apoptosis in response to ultraviolet B radiation and chemotherapeutic drug treatment. These results demonstrate the ability of a chemically modified oligonucleotide to alter splice site selection in an endogenous gene and illustrate a powerful tool to regulate cell survival.

A moderate reduction of Bcl-xL expression protects against tumorigenesis; however, it also increases susceptibility to tissue injury

“…Our results, however, suggest that the reduction of Bcl-x L is functionally dominant. Others have reached a similar conclusion (Taylor et al, 1999).…”

The future of antisense therapy: combination with anticancer treatments

“…However, since the crossspecificity for the proapoptotic bcl-x s could be undesirable, bcl-x PS ASOs designed to shift the splicing pattern of bcl-x pre-mRNA from the antiapopotic to the proapoptotic variant, or PS ASOs targeting a sequence in the bcl-x that is specific for bcl-x L , were tested. Antisense-mediated shift of bcl-x pre-mRNA splicing is effective in sensitizing cells to apoptosis and in enhancing the efficacy of standard anticancer regimens (Taylor et al, 1999;Mercatante et al, 2002). Similarly, specific downregulation of Bcl-x L (4259) in different tumor histotypes leads to activation of apoptosis, decreases cellular proliferation rate and resistance to cytotoxic chemotherapeutic agents Simoes-Wust et al, 2000;Heere-Ress et al, 2002;Vilenchik et al, 2002).…”

Bcl‐XL is a chemoresistance factor in human melanoma cells that can be inhibited by antisense therapy

“…[7][8][9] The Bcl-x gene is transcribed into 2 mRNAs through alternative splicing. The protein product of the longer Bcl-x mRNA (Bcl-x L ) functions as a repressor of programmed cell death, whereas the smaller mRNA species 10 encodes a protein capable of accelerating cell death. 7,11 Bcl-x L and Bcl-2 are prevalent in many solid tumors, including melanoma, where they potentially contribute to cell survival and drug resistance.…”