Early loss of Crebbp confers malignant stem cell properties on lymphoid progenitors.

Loss-of-function mutations of cyclic-AMP response element binding protein, binding protein (CREBBP) are prevalent in lymphoid malignancies. However, the tumour suppressor functions of CREBBP remain unclear. We demonstrate that loss of Crebbp in murine haematopoietic stem and progenitor cells (HSPCs) leads to increased development of B-cell lymphomas. This is preceded by accumulation of hyperproliferative lymphoid progenitors with a defective DNA damage response (DDR) due to a failure to acetylate p53. We identify a premalignant lymphoma stem cell population with decreased H3K27ac, which undergoes transcriptional and genetic evolution due to the altered DDR, resulting in lymphomagenesis. Importantly, when Crebbp is lost later in lymphopoiesis, cellular abnormalities are lost and tumour generation is attenuated. We also document that CREBBP mutations may occur in HSPCs from patients with CREBBP-mutated lymphoma. These data suggest that earlier loss of Crebbp is advantageous for lymphoid transformation and inform the cellular origins and subsequent evolution of lymphoid malignancies.

A comprehensive microarray-based DNA methylation study of 367 hematological neoplasms.

BACKGROUND: Alterations in the DNA methylation pattern are a hallmark of leukemias and lymphomas. However, most epigenetic studies in hematologic neoplasms (HNs) have focused either on the analysis of few candidate genes or many genes and few HN entities, and comprehensive studies are required. METHODOLOGY/PRINCIPAL FINDINGS: Here, we report for the first time a microarray-based DNA methylation study of 767 genes in 367 HNs diagnosed with 16 of the most representative B-cell (n = 203), T-cell (n = 30), and myeloid (n = 134) neoplasias, as well as 37 samples from different cell types of the hematopoietic system. Using appropriate controls of B-, T-, or myeloid cellular origin, we identified a total of 220 genes hypermethylated in at least one HN entity. In general, promoter hypermethylation was more frequent in lymphoid malignancies than in myeloid malignancies, being germinal center mature B-cell lymphomas as well as B and T precursor lymphoid neoplasias those entities with highest frequency of gene-associated DNA hypermethylation. We also observed a significant correlation between the number of hypermethylated and hypomethylated genes in several mature B-cell neoplasias, but not in precursor B- and T-cell leukemias. Most of the genes becoming hypermethylated contained promoters with high CpG content, and a significant fraction of them are targets of the polycomb repressor complex. Interestingly, T-cell prolymphocytic leukemias show low levels of DNA hypermethylation and a comparatively large number of hypomethylated genes, many of them showing an increased gene expression. CONCLUSIONS/SIGNIFICANCE: We have characterized the DNA methylation profile of a wide range of different HNs entities. As well as identifying genes showing aberrant DNA methylation in certain HN subtypes, we also detected six genes--DBC1, DIO3, FZD9, HS3ST2, MOS, and MYOD1--that were significantly hypermethylated in B-cell, T-cell, and myeloid malignancies. These might therefore play an important role in the development of different HNs.

Transmembrane adaptor molecules: a new category of lymphoid-cell markers.

Transmembrane adaptor proteins (of which 7 have been identified so far) are involved in receptor signaling in immune cells. They have only a short extracellular region, with most of the molecule comprising a substantial intracytoplasmic region carrying multiple tyrosine residues that can be phosphorylated by Src- or Syk-family kinases. In this paper, we report an immunohistologic study of 6 of these molecules in normal and neoplastic human tissue sections and show that they are restricted to subpopulations of lymphoid cells, being present in either T cells (LAT, LIME, and TRIM), B cells (NTAL), or subsets of both cell types (PAG and SIT). Their expression in neoplastic lymphoid cells broadly reflects that of normal lymphoid tissue, including the positivity of plasma cells and myeloma/plasmacytoma for LIME, NTAL, PAG, and SIT. However, this study also revealed some reactions that may be of diagnostic/prognostic value. For example, lymphocytic lymphoma and mantle-cell lymphoma showed similar profiles but differed clearly from follicle-center lymphoma, whereas PAG tended to be selectively expressed in germinal center-derived subsets of diffuse large B-cell lymphoma. These molecules represent a potentially important addition to the panel of immunophenotypic markers detectable in routine biopsies that can be used in hematopathologic studies.

The NFATc1 transcription factor is widely expressed in white cells and translocates from the cytoplasm to the nucleus in a subset of human lymphomas.

Stimulation of lymphoid cells via their surface receptors triggers signalling pathways that terminate in the nucleus, where they induce alterations in gene transcription. Nuclear factor of activated T cells (NFAT) transcription factors, involved in a major Ca2+-dependent signalling pathway, normally reside in the cytoplasm but re-locate to the nucleus when activation of the pathway (e.g. following ligation of antigen receptors) leads to their dephosphorylation. This study found that one member of the NFAT family (NFATc1/NFAT2) can be detected in routine biopsy samples, where it is seen in essentially all lymphoid cells, but is absent from the great majority of non-haematopoietic cells. An immunohistological evaluation of NFATc1 in almost 300 lymphomas showed that most neoplastic lymphoid cells also express NFATc1 as a cytoplasmic constituent, although it is absent in classical Hodgkin's disease and plasma cell proliferations. Of particular interest was the finding that NFATc1 was relocated to the nucleus in a minority of lymphoid neoplasms (usually diffuse large B-cell lymphomas or Burkitt lymphoma), presumably reflecting activation of the NFAT pathway. It would be of interest to correlate this feature with patterns of gene expression and also with prognosis, since it may identify a subset of human lymphoma that is distinct in its molecular and clinical features.

CD10 expression in extranodal dissemination of angioimmunoblastic T-cell lymphoma.

Angioimmunoblastic T-cell lymphoma (AITL) is a systemic disease that often has evidence of extranodal involvement at presentation. In a recent study of lymph nodes in AITL, we showed that the neoplastic T cells in most cases can be identified by aberrant expression of CD10. The aim of this study was to investigate whether CD10 expression by the neoplastic T cells is maintained in extranodal sites. Ten cases of AITL with histologic and immunophenotypic evidence of extranodal dissemination were studied. Seven cases of peripheral T-cell lymphoma unspecified (PTLu), that included biopsies of involved extranodal sites, two cases of enteropathy type T-cell lymphoma (ETTL), and one case of extranodal NK/T lymphoma, nasal type were selected as controls. Diagnostic lymph node biopsies and biopsies of extranodal sites were reviewed. PCR for T-cell clonality and single layer immunostaining for CD3, CD20, CD10, and CD21 and double layer immunostaining for CD20/CD10 were performed. All 10 cases of AITL had characteristic histologic features and molecular evidence of the disease in lymph node biopsies. In these cases, aberrant CD10 expression was maintained in the lung, cecum, tonsil, nasopharynx, and one of six involved bone marrow trephines. In these extranodal biopsies, the distribution of CD10-positive tumor cells correlated with that of the follicular dendritic cell meshwork (FDC). The five bone marrow trephines that lacked aberrant CD10 expression were devoid of morphologic and immunohistochemical evidence of FDC. In these five cases, there was evidence of aberrant CD10 expression in other involved sites that had FDC. The neoplastic cells in PTLu, ETTL, and extranodal NK/T lymphoma, nasal type were CD10 negative. Our data show that aberrant CD10 expression is a useful phenotypic marker for diagnosis of AITL in most involved extranodal sites, except bone marrow, and suggest a possible role of FDC in the pathogenesis of AITL.