Abundance of cyclin B1 regulates γ-radiation–induced apoptosis

Second allograft for hematologic relapse of acute leukemia after first allogeneic stem-cell transplantation from related and unrelated donors: the role of donor change

PURPOSE

To evaluate the role of a second allogeneic hematopoietic stem-cell transplantation (HSCT2) given for relapsed acute leukemia (AL) after related or unrelated first hematopoietic stem-cell transplantation (HSCT1) and to analyze the role of donor change for HSCT2 in both settings.

PATIENTS AND METHODS

We performed a retrospective registry study on 179 HSCT2s given for relapse after HSCT1 from matched related donors (n = 75) or unrelated donors (n = 104), using identical or alternative donors for HSCT2. Separate analyses were performed according to donor at HSCT1.

RESULTS

Independent of donor, 74% of patients achieved complete remission after HSCT2, and half of these patients experienced relapse again. Overall survival (OS) at 2 years was 25% ± 4% (39% ± 7% after related HSCT2; 19% ± 4% after unrelated HSCT2). Long-term survivors were observed even after two unrelated HSCT2s. Multivariate analysis for OS from HSCT2 confirmed established risk factors (remission duration after HSCT1: hazard ratio [HR], 2.37; 95% CI, 1.61 to 3.46; P < .001; stage at HSCT2: HR, 0.53; 95% CI, 0.34 to 0.83; P = .006). Outcome of HSCT2 was better after related HSCT1 than after unrelated HSCT1 (2-year OS: 37% ± 6% v 16% ± 4%, respectively; HR, 0.68; 95% CI, 0.47 to 0.98; P = .042, multivariate Cox regression). After both related and unrelated HSCT1, selecting a new donor for HSCT2 did not result in a relevant improvement in OS compared with HSCT2 from the original donor; however, donor change was not detrimental either.

CONCLUSION

After relapse from allogeneic HSCT1, HSCT2 can induce 2-year OS in approximately 25% of patients. Unrelated HSCT2 is feasible after related and unrelated HSCT1. Donor change for HSCT2 is a valid option. However, a clear advantage in terms of OS could not be demonstrated.

Repression of IRF-4 target genes in human T cell leukemia virus-1 infection

The human T cell leukemia/lymphotropic virus-1 (HTLV-I) is the etiologic agent of adult T cell leukemia (ATL), an aggressive and fatal leukemia of CD4+ T lymphocytes. Interferon regulatory factor-4 (IRF-4) was shown previously to be constitutively expressed in T cells infected with HTLV-1. In this study, we investigated the role of IRF-4 gene regulation in the context of HTLV-1 infection using gene array technology and IRF-4 expressing T cells. Many potential IRF-4 regulated genes were identified, the vast majority of which were repressed by IRF-4 expression. Cyclin B1, a G2-M checkpoint protein identified as an IRF-4 repressed gene in the array, was further characterized in the context of HTLV-1 infection. All HTLV-1 infected cell lines and ATL patient lymphocytes demonstrated a dramatic decrease in cyclin B1 levels; subsequent analysis of the cyclin B1 promoter identified two sites important in IRF-4 binding and repression of cyclin B1 expression. Furthermore, IRF-4-mediated repression of cyclin B1 led to a significant decrease in CDC2 kinase activity in HTLV-1 infected T cells. IRF-4 expression in HTLV-1 infected T cells also downregulated other genes implicated in the mitotic checkpoint as well as genes involved in actin cytoskeletal rearrangement, DNA repair, apoptosis, metastasis and immune recognition. Several of the identified genes are dysregulated in ATL and may provide important mechanistic information concerning pathways critical to the emergence of ATL.

[Mechanisms of radio-induced apoptosis]

A general overview of the activation mechanisms of programmed cell death or apoptosis following an irradiation is given in this review. First, are summarized the main induction pathways of radiation-induced apoptosis by which extracellular (tumor necrosis factor (TNF), Fas ligand, TNF-related apoptosis-inducing ligand (TRAIL)) and intracellular (mitochondria and caspases) signals are integrated. A second part is then devoted to the importance of p53 and of its regulators (ATR, ATM, DNA-PKcs) in the process of radiation-induced apoptosis. Thereafter, signal transduction pathways and more specially the role of some protein kinases (MEKK, SAPK/JNK, p38-MAPK) is treated. At last, a chapter concerns the clinical interest of radiation-induced apoptosis and the implication of apoptosis in the treatment of certain diseases.

alpha-, beta-, and gamma-Tubulin polymerization in response to DNA damage

Microtubules provide structural support for a cell and play key roles in cell motility, mitosis, and meiosis. They are also the targets of several anticancer agents, indicating their importance in maintaining cell viability. We have investigated the possibility that alterations in microtubule structure and tubulin polymerization may be part of the cellular response to DNA damage. In this report, we find that gamma-radiation stimulates the production and polymerization of alpha-, beta-, and gamma- tubulin in hematopoeitic cell lines (Ramos, DP16), leading to visible changes in microtubule structures. We have found that this microtubule reorganization can be prevented by caffeine, a drug that concomitantly inhibits DNA damage-induced cell cycle arrest and apoptosis. Our results support the idea that microtubule polymerization is an important facet of the mammalian response to DNA damage.