CD99 expression is positively regulated by Sp1 and is negatively regulated by Epstein-Barr virus latent membrane protein 1 through nuclear factor-kappaB

[Proteomic analysis and verification of protein expression after upregulation of human CD99 in Hodgkin lymphoma cell line L428]

Objective: To investigate the proteins expression difference after upregulation of human CD99 in Hodgkin Lymphoma cell line, L428 cell, and verify the function of differential proteins. Methods: The differential proteins were detected by two-dimensional fluorescence difference gel electrophoresis and mass spectrometry analysis, cluster analysis was done by GOfact. Results: There were 38 proteins screened out, of which 21 proteins were positively associated with CD99, while 17 proteins were negative. Among the 38 proteins, 32 proteins participated in biological process, and 35 proteins were involved in the composition and construction. And 28 proteins participated in multifaceted biological activities including antioxidation, protein binding, catalytic activity, regulation of enzyme, signal transduction, molecular structure, regulation of translation and ion transport. Conclusions: The changes of the differential proteins, correlated with cytoskeleton, cell differentiation, signal pathway and regulating gene expression, are closely relevant to the translation between Hodgkin/Reed-Sternberg and B lymphocyte cell.

Chronic stress induces CD99, suppresses autophagy, and affects spontaneous adipogenesis in human bone marrow stromal cells

BACKGROUND

Bone marrow-derived mesenchymal stromal cells (MSCs) are multipotent cells with a high constitutive level of autophagy and low expression of CD99. Under certain conditions, MSCs may develop tumorigenic properties. However, these transformation-induced conditions are largely unknown. Recently, we have identified an association between Hsp70, a main participant in cellular stress response and tumorigenesis, and CD99. Preliminary observations had revealed upregulation of both proteins in stressed long-term cultured MSCs. And so we hypothesized that CD99 is implicated in stress-induced mechanisms of cellular transformation in MSCs. Hence, we investigated the effects of prolonged stress on MSCs and the role of CD99 and autophagy in their survival.

METHODS

Human telomerase reverse transcriptase (hTERT) overexpressing immortalized MSCs and primary bone marrow stromal cells were used to investigate the influence of long-term serum deprivation and hypoxia on growth and differentiation of MSCs. Cell proliferation and apoptosis were evaluated using flow cytometry, differentiation capabilities of MSCs were assessed by immunohistochemical staining followed by microscopic examination. CD99, Hsp70 expression were analyzed using flow cytometry, western blotting, and reverse transcriptase polymerase chain reaction. Autophagy was explored with specific inhibitors using cell morphology examination and western blotting.

RESULTS

Chronic stress factors are able to change the morphology of MSCs and to inhibit spontaneous differentiation into adipocyte lineage. Furthermore, CD99 elevation and downregulation of p53 and p21 accompanied defective autophagy, which is usually associated with tumor formation. We found that inhibition of autophagy by chloroquine promoted cell detachment and modulated CD99 expression level whereas incorporation of CD99 recombinant protein into the cells suppressed autophagy.

CONCLUSIONS

Obtained results provide a model for chronic stress-induced transformation of MSCs via CD99 and may therefore be highly relevant to mesenchymal tumorigenesis.

CD99 expression and newly diagnosed diffuse large B-cell lymphoma treated with rituximab-CHOP immunochemotherapy

In order to evaluate prognostic value of CD99 expression in patients with diffuse large B-cell lymphoma (DLBCL) who underwent treatment with rituximab-CHOP immunochemotherapy, immunohistochemistry for CD99/CD10/BCL-2/BCL-6/MUM-1 was performed on nodal DLBCL specimens from 70 patients. Patients were classified as either germinal center B-cell (GCB) subtype or non-GCB subtype according to the Muris algorithm. A superior 2-year event-free survival (EFS) was observed in patients with the GCB subgroup, compared to those with the non-GCB subgroup (p = 0.034). The distribution of CD99 expression (29 patients; 41.4 %) did not show deviation according to subtype and was not prognostic for survival in the entire patient population. Among patients with the GCB subgroup, better EFS and overall survival (OS) were observed in CD99+ patients, compared to CD99- patients. Conversely, among patients with the non-GCB subgroup, inferior EFS and OS were reported in CD99+ patients. Superior 2-year EFS (p = 0.004) and 2-year OS (p = 0.003) were observed in patients with GCB/CD99+ and non-GCB/CD99- compared to the others, and the combination classification was found to be an independent prognostic factor.

Clinical significance of CD99 down-regulation in gastric adenocarcinoma

PURPOSE

CD99 is a cell adhesion molecule associated with human tumors. The aim of the present study was to characterize its role in the development and progression of human gastric adenocarcinoma.

EXPERIMENTAL DESIGN

The expression of CD99 was investigated in 283 gastric adenocarcinomas and related lesions and 9 gastric carcinoma cell lines. We also analyzed the methylation status of CD99 gene by using methylation-specific PCR and examined loss of heterozygosity (LOH) of this gene locus by using an intragenic marker. Moreover, we assessed whether SP1, a positive transcription factor for CD99, is expressed in these samples.

RESULTS

We found that the decreased expression of CD99 was strongly associated with poor survival and unfavorable clinicopathologic variables. Promoter region methylation (15 of 89, 16.9%) and LOH (21 of 74, 28.4%) were observed and significantly associated with CD99 down-regulation (P<0.05). In addition, most of the gastric adenocarcinoma cases with CD99 down-regulation had reduced expression of SP1 (47 of 103, 45.6%; P<0.01). This relationship between CD99 and SP1 was consolidated by using SP1 small interfering RNA transfection experiment and CD99 promoter luciferase assay. Furthermore, we showed that CD99 down-regulation was associated with proliferation and migration in gastric carcinoma cell line.

CONCLUSION

These observations suggest that CD99 down-regulation is a critical event in the progression of gastric adenocarcinoma, and CD99 promoter methylation, CD99 LOH, and SP1 down-regulation were responsible for the down-regulation of CD99.

Kinase activity and subcellular distribution of a chimeric green fluorescent protein-tagged Janus kinase 2

Janus kinase 2 (JAK2) is an essential intracellular signal transducer for numerous cytokines and hormones. To examine how JAK2 structural modifications can affect cellular physiology, we created expression vectors for chimeric proteins containing an enhanced green fluorescent protein (EGFP) fused to rat JAK2 (EGFP/rJAK2), and a kinase-inactive variant, EGFP/rJAK2(K882E). The properties of EGFP/rJAK2 were examined following transient transfection of COS-7 cells. EGFP/rJAK2 was expressed throughout the cell, and was found in subcellular membrane, cytosolic and nuclear fractions. Interestingly, EGFP/rJAK2 phosphorylated other proteins in situ without additional cytokine stimulation. Furthermore, despite a much higher level of tyrosine phosphorylation arising from in situ autophosphorylation, the in vitro radiolabelling autokinase activity of EGFP/rJAK2 was significantly less than that of the endogenous JAK2. These results reveal a technical limitation of the application of the "conventional" in vitro radiolabelling autokinase assay to hyperphosphorylated forms of the enzyme and illustrate the potential weaknesses in individual assays commonly used to determine JAK2's enzymatic activity and subcellular distribution. We also suggest that the EGFP/rJAK2 model can be very useful in studying JAK2-related cancers, because its ubiquitous distribution and abnormal constitutive hyperphosphorylation may distinguish it from the cytokine-regulated, membrane-proximal form of JAK2 associated with normal physiology.

Autoactivation of the Epstein-Barr virus oncogenic protein LMP1 during type II latency through opposite roles of the NF-kappaB and JNK signaling pathways

Epstein-Barr virus (EBV) is associated with several human malignancies where it expresses limited subsets of latent proteins. Of the latent proteins, latent membrane protein 1 (LMP1) is a potent transforming protein that constitutively induces multiple cell signaling pathways and contributes to EBV-associated oncogenesis. Regulation of LMP1 expression has been extensively described during the type III latency of EBV. Nevertheless, in the majority of EBV-associated tumors, the virus is commonly found to display a type II latency program in which it is still unknown which viral or cellular protein is really involved in maintaining LMP1 expression. Here, we demonstrate that LMP1 activates its own promoter pLMP1 through the JNK signaling pathway emerging from the TES2 domain. Our results also reveal that this activation is tightly controlled by LMP1, since pLMP1 is inhibited by LMP1-activated NF-kappaB signaling pathway. By using our physiological models of EBV-infected cells displaying type II latency as well as lymphoblastoid cell lines expressing a type III latency, we also demonstrate that this balanced autoregulation of LMP1 is shared by both latency programs. Finally, we show that this autoactivation is the most important mechanism to maintain LMP1 expression during the type II latency program of EBV.

The molecular basis for the generation of Hodgkin and Reed-Sternberg cells in Hodgkin's lymphoma

Hodgkin's lymphoma (HL) is a lymphoid neoplasm with a low frequency of malignant tumor cells, known as Hodgkin and Reed-Sternberg (H-RS) cells, in a background of mixed cellular infiltrates. Despite extensive studies on H-RS cells, the molecular mechanisms of their growth and regulation have remained uncertain for a long period. Recently, constitutively activated nuclear factor-kappaB (NF-kappaB) was reported to be a unique and common characteristic of H-RS cells that prevents the cells from undergoing apoptosis. NF-kappaB triggers proliferation and provides a molecular basis for these cells' aberrant growth and cytokine gene expression. In HL pathogenesis associated with Epstein-Barr virus infection, the activation of NF-kappaB is induced by viral latent membrane protein 1 (LMP1). Coupled with recent insights into the molecular mechanisms of activation of NF-kappaB signaling in H-RS cells, this review discusses a linkage between LMP1 and HL via CD99, which has recently been reported to be down-regulated by LMP1 through the NF-kappaB signaling pathway. This down-regulation leads to the generation of cells with H-RS phenotypes related to the clinical and histologic characteristics of HL.

Molecular biology of Hodgkin's lymphoma

Hodgkin's lymphoma (HL) is characterized by typical mononucleated Hodgkin and multinucleated Reed-Sternberg cells, which occur at low frequency in a mixed cellular infiltrate in the tumor tissue. Because of the rarity of these cells and their unusual immunophenotype, which is strikingly different from those of all normal hematopoietic cell types, the origin of these cells and their clonality have long been unclear. Single-cell studies of rearranged immunoglobulin genes showed that Hodgkin and Reed-Sternberg (HRS) cells represent clonal tumor-cell populations derived from germinal center B cells. In classical HL, the detection of obviously crippling immunoglobulin gene mutations in a fraction of the cases suggests that HRS cells may derive from germinal center B cells that have lost the capacity to be positively selected by antigen and that normally would have undergone apoptosis. In rare cases, HRS cells represent transformed T lymphocytes. The transforming events involved in malignant transformation of HRS cells are still largely unknown. Constitutive activation of the transcription factor NFkappaB, which can, for example, be induced through Epstein-Barr virus transformation of HRS cells or destructive somatic mutations of the inhibitor of NFkappaB, is likely to be a key event in HL pathogenesis. Significant progress has been made in our understanding of the cellular interactions in HL tissues, which are mainly mediated by a large variety of cytokines and chemokines.

Inhibition of transforming growth factor beta signaling and Smad-dependent activation of transcription by the Latent Membrane Protein 1 of Epstein-Barr virus

Inhibition of transforming growth factor beta (TGFbeta) signaling by the Epstein-Barr virus Latent Membrane Protein 1 (LMP1) may account, at least in part, for the oncogenic activity of LMP1. We found that LMP1 is a potent inhibitor of TGFbeta signaling and Smad-dependent activation of transcription in 293 epithelial cells and COS-7 fibroblasts. LMP1 strongly inhibited the uninduced and the Smad-inducible activity of the promoters of the human p21/WAF1/Cip1 gene and the mouse Smad7 gene. Inhibition of TGFbeta signaling and Smad-dependent activation of transcription by LMP1 was greatly reduced by deletion of both C-terminal activating regions 1 and 2 of LMP1 as well as by overexpression of a non-degradable form of IkappaB. In contrast, specific inhibitors of p38 kinase or MEK kinase did not reverse the inhibitory activity of LMP1. TGFbeta signaling was enhanced by overexpression of dominant negative forms of the LMP1 effectors TRAF2, NIK, and IKKbeta and was abolished by overexpression of p65/RelA or a p50/p65 fusion protein. Deletion of the transactivation domain of p65 abolished its inhibitory activity. Immunoblotting and immunofluorescence microscopy indicated that suppression of TGFbeta signaling and Smad transcriptional activity by LMP1 was not due to Smad degradation or cytoplasmic retention suggesting that LMP1 affects the nuclear function of Smad proteins. Our data are consistent with an essential role of NF-kappaB activation by LMP1 in the inhibition of TGFbeta signaling and Smad-mediated transcriptional responses.

Epstein-Barr virus LMP-1 natural sequence variants differ in their potential to activate cellular signaling pathways

The latent membrane protein 1 (LMP-1) oncogene of Epstein-Barr virus (EBV) is believed to contribute to the development of many EBV-associated tumors, and there is evidence that sequence variation can affect some functions of LMP-1. Most studies have been restricted to the prototype B95.8 LMP-1 gene and genes isolated from EBV of nasopharyngeal carcinoma (NPC) patients. Here, we analyzed the signaling functions of LMP-1 from a panel of nine EBV isolates, including representatives of four defined groups of European LMP-1 variants (groups A to D [K. Sandvej, J. W. Gratama, M. Munch, X. G. Zhou, R. L. Bolhuis, B. S. Andresen, N. Gregersen, and S. Hamilton-Dutoit, Blood 90:323-330, 1997]) and Chinese NPC-derived LMP-1. Chinese and group D variants activated the transcription factor NF-kappa B two- to threefold more efficiently than B95.8 LMP-1, while Chinese, group B, and group D variants similarly activated activator protein 1 (AP-1) transcription more efficiently than did B95.8 LMP-1. However, there were no amino acid substitutions in the core binding regions for tumor necrosis factor receptor-associated adapter proteins known to mediate NF-kappa B and AP-1 activation. In contrast, despite sequence variation in the proposed Janus kinase 3 binding region, STAT activation was remarkably constant among the panel of LMP-1 variants. Analysis of the induction of CD54 (intercellular adhesion molecule 1) protein expression by the LMP-1 variants showed differences that did not correlate with either NF-kappa B or AP-1. Therefore, while the defined sequence variant groups do correlate with LMP-1 function, the results highlight the fact that the relationship between sequence variation and signaling function is extremely complex. It appears unlikely that one particular amino acid substitution or deletion will define a disease-associated variant of LMP-1.