Mechanism of action of interleukin-2 (IL-2)-Bax, an apoptosis-inducing chimaeric protein targeted against cells expressing the IL-2 receptor.
The chimaeric protein interleukin-2 (IL-2)-Bax was designed to target and kill specific cell populations expressing the IL-2 receptor. However, it is not well understood how IL-2-Bax causes target cells to die. In the present study, we investigated the pathway of apoptosis evoked by IL-2-Bax and the possible involvement of endogenous Bax in this process. We report here that, upon internalization of IL-2-Bax into target cells, it is localized first mainly in the nucleus, and only later is it translocated to the mitochondria. Similarly, endogenous Bax is also partially localized in the nucleus, and accumulates mainly in this compartment soon after physiological triggering of apoptosis. Despite the fact that Bax has no nuclear localization sequence, our data suggest that Bax has one or more physiological roles and/or substrates within the nucleus. Indeed, a dramatic repression of nuclear Tax protein expression was induced following treatment of HUT-102 cells with IL-2-Bax, similar to what occurs following serum deprivation of these cells. Unexpectedly, induction of apoptosis using IL-2-Bax was preceded by enhanced expression of newly synthesized Bax protein and suppression of Bcl-2. This imbalance between the pro- and anti-apoptotic genes was associated with p53 induction, although IL-2-Bax activity was also evident in cells lacking p53 expression. By studying the mechanism of action of IL-2-Bax, we were able to follow the intrinsic events and their cascade that culminates in cell death. We have shown that the ability of IL-2-Bax to affect the intracellular apoptotic machinery within the target cells, and to cause the cells to die, uses a mechanism similar to that induced following a normal apoptotic signal.
Aqeilan
Rami
R
Department of Cellular Biochemistry and Human Genetics, Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel.
Kedar
Rotem
R
Ben-Yehudah
Ahmi
A
Lorberboum-Galski
Haya
H
D017209:Apoptosis / Q000187:drug effects*; D001483:Base Sequence; D017931:DNA Primers; D006801:Humans; D007376:Interleukin-2 / Q000737:chemistry / Q000494:pharmacology*; D021381:Protein Transport; D011518:Proto-Oncogene Proteins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013347:Subcellular Fractions / Q000378:metabolism; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D051028:bcl-2-Associated X Protein
C494826:BAX protein, human; D017931:DNA Primers; D007376:Interleukin-2; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein