BACKGROUND Aging is characterized by a progressive decline in immune surveillance that favors tumor development in older patients. One of the mechanisms used by malignant cells to escape immune surveillance is genetic or epigenetic modifications of tumor suppressor genes. Studies in B-cells and our previous report on the correlation between 6q deletion and progression into a T cell lymphoproliferative disease, identifying the BACH2 gene as a candidate tumor suppressor gene. Together, BACH2 and PRDM1 are described as having a fundamental role in oncogenesis, differentiation and apoptosis control of B and T lymphocytes during oxidative stress. Furthermore, several studies in mice model suggested that BACH2 gene is sensitive to DNA damage during aging and plays a role in the cellular senescence process. The impact of these genes in the immune response of the older adult is unclear. OUR HYPOTHESIS 1. Recent reports (including our previous study) on the transcription factor BACH2 and PRDM1 have highlighted their impact on immunological changes. It has been shown that BACH2 is highly sensitive to transcription-blocking DNA lesions in aged mice. Despite the growing interest in BACH's role, there have been many studies in mice models, studies on BACH2 in humans are still limited. This concept prompted us to investigate the variation of BACH2 and PRDM1 expression with age in major lymphocyte subsets from healthy individuals. 2. Apoptosis and senescence are two types of cellular response affected by cancer and aging processes, albeit through different mechanisms. Carcinogenesis is associated with a progressive reduction in the ability of the cells to trigger apoptosis and senescence. The lymphocytes apoptosis process and the markers of cell senescence were thus studied in both populations. 3. Chronic lymphocytic leukemia, one of the aging-related diseases, is characterized by the accumulation of “anergic” phenotypes in both B-cells and T-cells. In chronic lymphocytic leukemia, malignant cell anergy is associated with failure of inducing PRDM1 (BLIMP1), a critical regulator of differentiation into plasma cells, and that epigenetic modification account for such failure. We thus examined the expression of specific transcription factors BACH2 and PRDM1 in the leukemic lymphocytes subsets and compared the results with age-matched normal population. POPULATION & METHODS Blood samples were obtained from 60 healthy donors, aged from 20 to 90 years, and 41 untreated chronic lymphocytic leukemia were studied. Lymphocyte subsets (CD19+ B-cells, CD8 T-cells, CD4 T-cells, CD4 naïve T-cells, CD4 effector memory T-cells) were isolated for subsequent molecular analyses using the MACS Technology (Miltenyi), with the purity of each lymphocyte subpopulation between 95%-99%. BACH2, PRDM1, IL-4, IFNG, TP53, CDKN2A (p16INK4A), PDCD1 (PD-1) and CD274 (PD-L1) mRNA transcripts were quantified using qRT-PCR. BACH2 protein expression was examined by Western blotting. To investigate BACH2-target genes in apoptosis, we performed a “Human Apoptosis EpiTect ChIP qPCR Array” profiles including 84 key genes involved in programmed cell death. Etoposide was used to induce intracellular oxidative stress followed by cell apoptosis. Apoptotic cells were identified with the annexin-V-FITC apoptosis detection kit (BD Pharmingen). To measure ß-galactosidase by flow cytometry, we used Fluorescein-di-beta-D-galactopyranoside as a substrate for beta-galactosidase (Molecular Probes).RESULTS 1. BACH2 and PRDM1 gene expression were strongly correlated with age in healthy donor’s major lymphocyte subsets. BACH2 mRNA expression declined by age, with statistically significant differences observed in all lymphocyte subsets: CD4+, CD4+ naïve, CD4+ memory, CD8+ T-cells and CD19+ B-cells (p<0.0001, <0.0001, 0.0118, <0.0001 and 0.0004 respectively). In contrast, PRDM1 gene expression significantly increased with age in the same subpopulations. The phenotypic changes of immune lymphocytes are related to the BACH2 and PRDM1 gene expression. Along with the decline of BACH2, the older group had a severe decrease in number and quality of cytotoxic T-cells (p=0.0005 and <0.0001), while increasing the rate exhausted T-cells that highly expressed of PD-1 and PD-L1. Both PCCD1 (PD-1) and CD274 (PD-L1) gene expression had inversely correlated with BACH2 in the same lymphocyte subsets (p=0.0342; 0.0254 and 0.0429 respectively). Western blotting analysis demonstrated that BACH2 protein expressions in the T and B cell subpopulations significantly correlated with transcript expression. 2. Age-related BACH2 down-regulation enhanced the increasing of senescent cells and the resistance to apoptosis in the major lymphocyte subsets. We, further, found the correlation of BACH2 with senescence markers, such as p16INK4A (CDKN2A) and SA-β-GAL along with loss of CD28+ on T-lymphocytes. ChIP-qPCR Array demonstrated that BACH2 bound directly several genes involved in programmed cell death. A reduction in apoptosis was observed with age in CD4+ T-cells and CD19+ B-cells (p=0.03 in both subpopulations). As recently reported for BACH2-deficient mice, our data show that BACH2 down-regulation is strongly correlated with a decrease in CD4+ T-cell and CD19+ B-cell apoptosis (r=0.57 and 0.61). 3. Decreases in BACH2 mRNA expression were greater in CD4+ and CD8+ T-cells, as well as leukemic B-cell subpopulations from untreated CLL patients, compared with age-matched healthy donors (p=0.0006; 0.0003 and 0.0083, respectively). As expected, PRDM1 was significantly upregulated in the CD4+ and CD8+ T-cell subpopulations (p=0.003 and 0.001, respectively) from CLL patients but not their leukemic B-cells. CONCLUSION In this research work, we examined BACH2 and PRDM1 gene expression to investigate its potential as a predictive marker of aging. Our data suggest BACH2 and PRDM1 mRNA expression, in the inverse correlation, associated with the phenotypic changes of immune lymphocytes in aging. Age-related BACH2 down-regulation enhanced the increasing of exhausted phenotypes, senescent cells and resistance to cell apoptosis. BACH2 and PRDM1 could involve in cellular and immunological functions deterioration of the immunosenescence process. Further investigations on BACH2 and PRDM1 genetic mutations provide a better understanding of the role of the unbalanced expression of those genes in lymphocytes functions and survival according to age. / Doctorat en Sciences biomédicales et pharmaceutiques (Médecine) / info:eu-repo/semantics/nonPublished

The human positive regulatory domain I binding factor 1 (PRDI-BF1/PRDM1) promotes differentiation of mature B cells into antibody secreting plasma cells. In contrast ectopic expression of PRDM1 in lymphoma cells can lead to inhibition of proliferation or apoptosis. However, little is currently known about the regulation of PRDM1. The first study presented demonstrates that in lymphoma cells stimulation through the B cell receptor rapidly induces endogenous PRDM1 at the level of transcription. This study provides evidence that the PRDM1 promoter is preloaded and poised for activation in the B cell lines. The transcription factor PU.1 is shown to be required for B cell receptor induced expression of PRDM1 in lymphoma cells and in PU.1 positive myeloma cells. Furthermore, activation is associated with loss of the co-repressor TLE4 from the PU.1 complex. The second study establishes the requirement for PRDM1 in Mantle cell lymphoma (MCL) response to Bortezomib. MCL, an aggressive form of B cell lymphoma, has poor disease- free survival rate. The proteasome inhibitor, Bortezomib, is approved for treatment of relapsed and refractory MCL. However, the precise mechanism of action of Bortezomib is not well understood. Bortezomib rapidly induces transcription of PRDM1 along with apoptosis in MCL cell lines and primary MCL tumor samples. Knockdown of PRDM1 inhibits Bortezomib-induced apoptosis, while ectopic expression of PRDM1 alone leads to apoptosis in MCL. MKI67 and PCNA, which are required for proliferation and survival, were identified as novel direct targets of PRDM1 in MCL. Chromatin immunoprecipitation and knockdown studies reveal specific repression of MKI67 and PCNA is mediated by PRDM1 in response to Bortezomib. Furthermore promoter studies demonstrate that PRDM1 functions through a specific site in the proximal promoter region of PCNA and through a distal upstream repression domain on the MKI67 promoter. Together these findings establish PRDM1 as a key mediator of Bortezomib activity in MCL through suppression of proliferation and survival genes. The third study presented demonstrates use of Tandem affinity purification technique followed by mass spectrometry to identify PRDM1 and Reptin52 protein interactions. The observations in this study provide preliminary evidence of novel mechanism of regulation of PRDM1 protein function.

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Dissertation (Ph.D.)--University of South Florida, 2006. / Includes vita. Includes bibliographical references (leaves 119-141). Also available online.