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Background: A wide range of hematologic malignancies arises from numerous cell types. In an attempt to offer a new target for treating B-cell malignancies, in this study, the authors tested the possibility of using the CD40/CD40L system as a common targeting system for the various malignancies in this group., Methods: Two chimeric proteins, soluble CD40 ligand (sCD40L)-caspase 3 (sCD40L-l-Caspase3) and sCD40L-pseudomonas exotoxin 38 (PE38) (sCD40L-l-PE38), were constructed, expressed, and partially purified. The ability of the chimeric proteins to kill tumor cells that expressed CD40 was tested by using proliferation assays. In addition, the induction of apoptosis in treated cells was followed by measuring expression levels of apoptotic proteins using real-time polymerases chain reaction analysis, caspase 3 enzymatic activity, and tracking changes in the cell cycle with fluorescence-activated cell-sorting analysis., Results: The chimeric proteins exhibited concentration-dependent and time-dependent killing ability. The new chimeric proteins had no effect in several carcinoma cell lines that did not express the CD40 receptor. Treating tumor cells with sCD40L-based chimeric proteins led to internalization of the fusion proteins into the cell cytoplasm of B cells. Shortly after treatment, a sharp rise in B-cell chronic lymphocytic leukemia/lymphoma 2 (Bcl2) expression levels occurred. Approximately 36 hours after the initiation of treatment, Bcl2 levels dropped, whereas Bcl2-associated X protein (Bax) expression levels rose, pushing the cells toward apoptosis. Concomitantly, caspase 3 RNA levels rose., Conclusions: sCD40L-based chimeric proteins were able to bind and internalize into B cells that expressed the CD40 receptor and specifically and efficiently induced apoptotic death. Moreover, the current results validated for the first time the ability of sCD40L to serve as a direct delivery system for targeted molecules. sCD40L-based chimeric cytotoxic proteins offer a new weapon in the everlasting war against cancer., (Copyright © 2012 American Cancer Society.)

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.