p53 family members in myogenic differentiation and rhabdomyosarcoma development.

The p53 family comprises the tumor suppressor p53 and the structural homologs p63 and p73. How the three family members cooperate in tumor suppression remains unclear. Here, we report different but complementary functions of the individual members for regulating retinoblastoma protein (RB) function during myogenic differentiation. Whereas p53 transactivates the retinoblastoma gene, p63 and p73 induce the cyclin-dependent kinase inhibitor p57 to maintain RB in an active, hypophosphorylated state. DeltaNp73 inhibits these functions of the p53 family in differentiation control, prevents myogenic differentiation, and enables cooperating oncogenes to transform myoblasts to tumorigenicity. DeltaNp73 is frequently overexpressed in rhabdomyosarcoma and essential for tumor progression in vivo. These findings establish differentiation control as a key tumor suppressor activity of the p53 family.

p73 poses a barrier to malignant transformation by limiting anchorage-independent growth.

p53 is known to prevent tumour formation by restricting the proliferation of damaged or oncogene-expressing cells. In contrast, how the p53 family member p73 suppresses tumour formation remains elusive. Using a step-wise transformation protocol for human cells, we show that, in premalignant stages, expression of the transactivation-competent p73 isoform TAp73 is triggered in response to pRB pathway alterations. TAp73 expression at this stage of transformation results in increased sensitivity to chemotherapeutic drugs and oxidative stress and inhibits proliferation and survival at high cell density. Importantly, TAp73 triggers a transcriptional programme to prevent anchorage-independent growth, which is considered a crucial hallmark of fully transformed cells. An essential suppressor of anchorage-independent growth is KCNK1, which is directly transactivated by TAp73 and commonly downregulated in glioma, melanoma and ovarian cancer. Oncogenic Ras switches p73 expression from TAp73 to the oncogenic deltaNp73 isoform in a phosphatidyl-inositol 3-kinase-dependent manner. Our results implicate TAp73 as a barrier to anchorage-independent growth and indicate that downregulation of TAp73 is a key transforming activity of oncogenic Ras mutants.

C-terminal diversity within the p53 family accounts for differences in DNA binding and transcriptional activity.

The p53 family is known as a family of transcription factors with functions in tumor suppression and development. Whereas the central DNA-binding domain is highly conserved among the three family members p53, p63 and p73, the C-terminal domains (CTDs) are diverse and subject to alternative splicing and post-translational modification. Here we demonstrate that the CTDs strongly influence DNA binding and transcriptional activity: while p53 and the p73 isoform p73gamma have basic CTDs and form weak sequence-specific protein-DNA complexes, the major p73 isoforms have neutral CTDs and bind DNA strongly. A basic CTD has been previously shown to enable sliding along the DNA backbone and to facilitate the search for binding sites in the complex genome. Our experiments, however, reveal that a basic CTD also reduces protein-DNA complex stability, intranuclear mobility, promoter occupancy in vivo, target gene activation and induction of cell cycle arrest or apoptosis. A basic CTD therefore provides both positive and negative regulatory functions presumably to enable rapid switching of protein activity in response to stress. The different DNA-binding characteristics of the p53 family members could therefore reflect their predominant role in the cellular stress response (p53) or developmental processes (p73).

IgVH mutational status and clonality analysis of Richter's transformation: diffuse large B-cell lymphoma and Hodgkin lymphoma in association with B-cell chronic lymphocytic leukemia (B-CLL) represent 2 different pathways of disease evolution.

Approximately 5% of B-cell chronic lymphocytic leukemia (B-CLL) patients develop a secondary aggressive lymphoma, usually of diffuse large B-cell type (DLBCL), termed Richter's transformation (RT). Rarely, classic Hodgkin lymphoma (HL) is observed. Published small series suggest that tumor cells in DLBCL and HL can be clonally identical to the B-CLL clone or arise as an independent, secondary lymphoma. We describe the morphology, immunophenotype, and clinical features of 34 classic RT patients with DLBCL, 6 cases of B-CLL with HL, and 8 cases with scattered CD30-positive Hodgkin and Reed-Sternberg (HRS)-like cells. The clonal relationship of the 2 components was analyzed using sequencing analysis of immunoglobulin heavy chain variable region (IgVH) genes. In classic RT, 18/23 B-CLL cases (78%) showed clonal progression to DLBCL with identical IgVH sequences in both lymphoma components, whereas in 5 cases (22%) the DLBCL was clonally unrelated. Among clonally related RT samples, 73% carried unmutated IgVH genes, whereas 4/5 unrelated cases were mutated. Immunophenotypically, most cases of DLBCL irrespective of clonal relatedness showed significant differences in phenotype compared with the B-CLL, with common loss of CD5 and CD23. Using immuno-laser capture microdissection, sequencing of the IgVH CDR3 region of isolated HRS cells showed that 2/2 cases with HL were clonally unrelated, whereas they were clonally identical in 1/2 cases of B-CLL with scattered HRS-like cells. HRS or HRS-like cells in all 3 unrelated cases showed evidence of Epstein-Barr virus infection. Of interest, 5/6 cases of B-CLL with HL, and 5/6 cases of B-CLL with HRS cells showed mutated IgVH genes.

Diagnostic and prognostic significance of gene expression profiling in lymphomas.

Gene expression profiling is a powerful tool to uncover complex molecular networks in cancer and, specifically, in malignant lymphomas. Within diffuse large B-cell lymphomas (DLBCL), two major molecular subtypes, the activated B-cell-like (ABC) and the germinal center B-cell-like (GCB) DLBCL, can be defined. Compared to GCB DLBCL, ABC DLBCL shows a vast difference in gene expression and constitutively expresses NFkappaB and its target genes. In retrospective analyses, the molecular phenotype of ABC DLBCL is associated with inferior survival. Gene expression profiling furthermore allows the molecular separation of Burkitt lymphoma (BL) from DLBCL and reveals a Burkitt-specific signature which is also expressed by a subset of tumors that are currently classified as DLBCL. Whether patients with a DLBCL displaying a Burkitt-specific gene expression signature may benefit from alternative therapeutic approaches will have to be determined in future prospective clinical trials. In follicular lymphoma (FL), two outcome-related signatures, termed Immune response 1 (IR1) and Immune response 2 (IR2), have been identified by gene expression profiling, indicating a significant role of the microenvironment in tumor development and progression. IR1, composed of genes mostly expressed by T-cells, was found to be associated with a more favorable clinical course, and IR2, enriched for genes expressed by macrophages and follicular dendritic cells, was found to be associated with an inferior clinical course. In mantle cell lymphoma (MCL), a gene expression-based proliferation signature of 20 different genes was identified that is able to predict survival of MCL patients in a linear fashion. Future efforts will have to be directed towards the translation of relevant molecular diagnostic and prognostic markers derived from the wealth of gene expression data into clinical tests and towards the development of novel, targeted therapies.

Anticancer drugs of tomorrow: apoptotic pathways as targets for drug design.

Apoptosis or programmed cell death is a set of ordered events that enables the selective removal of cells from tissue and is essential for homeostasis and proper function of multicellular organisms. Components of this signaling network, which include ligands, such as CD95, tumor necrosis factor (TNF) and TNF-related apoptosis-inducing ligand, as well as downstream molecules, such as caspases, Bcl-2 family members, and inhibitor-of-apoptosis proteins, which trigger and regulate apoptosis, are crucial targets for conventional drug development and gene therapy of cancer and other diseases. Here, we focus on apoptotic pathways and propose new potential molecular targets that could prove effective in controlling cell death in the clinical setting.

Application of integrated transcriptomic, proteomic and metabolomic profiling for the delineation of mechanisms of drug induced cell stress.

High content omic techniques in combination with stable human in vitro cell culture systems have the potential to improve on current pre-clinical safety regimes by providing detailed mechanistic information of altered cellular processes. Here we investigated the added benefit of integrating transcriptomics, proteomics and metabolomics together with pharmacokinetics for drug testing regimes. Cultured human renal epithelial cells (RPTEC/TERT1) were exposed to the nephrotoxin Cyclosporine A (CsA) at therapeutic and supratherapeutic concentrations for 14days. CsA was quantified in supernatants and cellular lysates by LC-MS/MS for kinetic modeling. There was a rapid cellular uptake and accumulation of CsA, with a non-linear relationship between intracellular and applied concentrations. CsA at 15µM induced mitochondrial disturbances and activation of the Nrf2-oxidative-damage and the unfolded protein-response pathways. All three omic streams provided complementary information, especially pertaining to Nrf2 and ATF4 activation. No stress induction was detected with 5µM CsA; however, both concentrations resulted in a maximal secretion of cyclophilin B. The study demonstrates for the first time that CsA-induced stress is not directly linked to its primary pharmacology. In addition we demonstrate the power of integrated omics for the elucidation of signaling cascades brought about by compound induced cell stress.

Potentially oncogenic B-cell activation-induced smaller isoforms of FOXP1 are highly expressed in the activated B cell-like subtype of DLBCL.

The FOXP1 forkhead transcription factor is targeted by recurrent chromosome translocations in several subtypes of B-cell non-Hodgkin lymphomas, where high-level FOXP1 protein expression has been linked to a poor prognosis. Western blotting studies of diffuse large B-cell lymphoma (DLBCL) cell lines unexpectedly identified the atypical high-level expression of 2 smaller, 60 to 65 kDa, FOXP1 isoforms in all 5 of those with the activated B cell (ABC)-like DLBCL subtype and in a subgroup of primary DLBCL. The anti-FOXP1 (JC12) monoclonal antibody cannot distinguish FOXP1 isoforms by immunohistochemistry, a finding that may be clinically relevant as high-level expression of the full-length FOXP1 protein was observed in some germinal center-derived DLBCLs. ABC-like DLBCL-derived cell lines were observed to express 2 novel, alternatively spliced FOXP1 mRNA isoforms, encoding N-terminally truncated proteins. These transcripts and the smaller protein isoforms were induced as a consequence of normal B-cell activation, which thus represents an additional mechanism for up-regulating FOXP1 expression in lymphomas. The expression of potentially oncogenic smaller FOXP1 isoforms may resolve the previously contradictory findings that FOXP1 represents a favorable prognostic marker in breast cancer and an adverse risk factor in B-cell lymphomas.

Comprehensive analysis of homeobox genes in Hodgkin lymphoma cell lines identifies dysregulated expression of HOXB9 mediated via ERK5 signaling and BMI1.

Many members of the nearly 200-strong homeobox gene family have been implicated in cancer, mostly following ectopic expression. In this study we analyzed homeobox gene expression in Hodgkin lymphoma (HL) cell lines. Both reverse transcription-polymerase chain reaction (RT-PCR) using degenerate primers and microarray profiling identified consistently up-regulated HOXB9 expression. Analysis of HOXB9 regulation in HL cells revealed E2F3A and BMI1 as activator and repressor, respectively. Furthermore, a constitutively active ERK5 pathway was identified in all HL cell lines analyzed as well as primary HL cells. Our data show that ERK5 probably mediates HOXB9 expression by repressing BMI1. In addition, expression analysis of the neighboring microRNA gene mir-196a1 revealed coregulation with HOXB9. Functional analysis of HOXB9 by knockdown and overexpression assays indicated their influence on both proliferation and apoptosis in HL cells. In summary, we identified up-regulation of HOXB9 in HL mediated by constitutively active ERK5 signaling which may represent novel therapeutic targets in HL.

Diffuse large B-cell lymphoma subgroups have distinct genetic profiles that influence tumor biology and improve gene-expression-based survival prediction.

Gene-expression profiling has identified 3 major subgroups of diffuse large B-cell lymphoma (DLBCL): germinal center B-cell-like (GCB), activated B-cell-like (ABC), and primary mediastinal DLBCL (PMBCL). Using comparative genomic hybridization (CGH), we investigated the genetic alterations of 224 cases of untreated DLBCL (87 GCB-DLBCL, 77 ABC-DLBCL, 19 PMBCL, and 41 unclassified DLBCL) previously characterized by gene-expression profiling. The DLBCL subgroups differed significantly in the frequency of particular chromosomal aberrations. ABC-DLBCL had frequent trisomy 3, gains of 3q and 18q21-q22, and losses of 6q21-q22, whereas GCB-DLBCL had frequent gains of 12q12, and PMBCL had gains of 9p21-pter and 2p14-p16. Parallel analysis of CGH alterations, locus-specific gene-expression profiles, and global gene-expression signatures revealed that DNA amplifications and gains had a substantial impact on the expression of genes in the involved chromosomal regions, and some genes were overexpressed in a DLBCL subgroup-specific fashion. Unexpectedly, specific chromosomal alterations were associated with significant changes in gene-expression signatures that reflect various aspects of lymphoma cell biology as well as the host response to the lymphoma. In addition, gains involving the chromosomal region 3p11-p12 provided prognostic information that was statistically independent of the previously defined gene-expression-based survival model, thereby improving its predictive power.

Selective loss of regulatory T cells in thymomas.

Myasthenia gravis (MG) is the prime autoimmune manifestation of thymomas. We investigated the generation of T cells with a regulatory phenotype (T(R)) in thymomas with and without associated MG. In patients with MG(+) thymomas, maturation and export of T(R) cells but not of other T-cell subsets was significantly reduced. We conclude that imbalance between effector and regulatory T cells in thymomas may be involved in modulation of onset and/or severity of MG.