CD74 induces TAp63 expression leading to B-cell survival

TAp63 is a transcriptional target of NF-kappaB

The p53 homologue p63 encodes multiple protein isoforms either with (TA) or without (DeltaN) the N-terminal transactivation domain. Accumulating evidence indicates that TAp63 plays an important role in various biological processes, including cell proliferation, differentiation, and apoptosis. However, how TAp63 is regulated remains largely unclear. In this study, we demonstrate that NF-kappaB induces TAp63 gene expression. The responsible elements for NF-kappaB-mediated TAp63 induction are located within the region from -784 to -296 bp in the TAp63 promoter, which contains two NF-kappaB binding sites. Ectopic expression of RelA stimulates TAp63 promoter-driven reporter activity and increases endogenous TAp63 mRNA levels. Inhibition of NF-kappaB by IkappaBalpha super-repressor or with a chemical inhibitor leads to down regulation of TAp63 mRNA expression and activity. In addition, mutations in the critical NF-kappaB-binding sites significantly abolish the effects of NF-kappaB on TAp63. Activation of NF-kappaB by TNFalpha enhances p50/RelA binding to the NF-kappaB binding sites. Furthermore, we show that an Sp1 site adjacent to the NF-kappaB sites plays a role in NF-kappaB-mediated upregulation of TAp63. Taken together, these data reveal that TAp63 is a transcriptional target of NF-kappaB, which may play a role in cell proliferation, differentiation and survival upon NF-kappaB activation by various stimuli.

c-Met and its ligand hepatocyte growth factor/scatter factor regulate mature B cell survival in a pathway induced by CD74

The signals regulating the survival of mature splenic B cells have become a major focus in recent studies of B cell immunology. Durable B cell persistence in the periphery is dependent on survival signals that are transduced by cell surface receptors. In this study, we describe a novel biological mechanism involved in mature B cell homeostasis, the hepatocyte growth factor/scatter factor (HGF)/c-Met pathway. We demonstrate that c-Met activation by HGF leads to a survival cascade, whereas its blockade results in induction of mature B cell death. Our results emphasize a unique and critical function for c-Met signaling in the previously described macrophage migration inhibitory factor/CD74-induced survival pathway. Macrophage migration inhibitory factor recruits c-Met to the CD74/CD44 complex and thereby enables the induction of a signaling cascade within the cell. This signal results in HGF secretion, which stimulates the survival of the mature B cell population in an autocrine manner. Thus, the CD74-HGF/c-Met axis defines a novel physiologic survival pathway in mature B cells, resulting in the control of the humoral immune response.

CD74 is a survival receptor on colon epithelial cells

AIM: To investigate the expression and function of CD74 in normal murine colon epithelial cells (CEC) and colon carcinoma cells.

METHODS: Expression of CD74 mRNA and protein were measured by reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting and fluorescence-activated cell sorter (FACS). The effect of migration inhibitory factor (MIF) on the survival of normal CEC from C57BL/6, NOD/SCID, and CD74 deficient mice both in vitro and in vivo, and on the CT26 carcinoma cell line was analyzed by (quantitative) qRT-PCR, RT-PCR, Western blotting and FACS.

RESULTS: CD74 was found to be expressed on normal CEC. Stimulation of CD74 by MIF induced a signaling cascade leading to up-regulation of Bcl-2 expression, resulting in a significant increased survival of CEC. CD74 was also expressed on the CT26 colon carcinoma cell line and its stimulation by MIF resulted in enhanced cell survival, up-regulation of Akt phosphorylation and Bcl-2 expression.

CONCLUSION: CD74 is expressed on CEC and colon carcinoma cells and serves as a survival receptor in these cells. These results may have implications on colorectal cancer research.

A retroviral mutagenesis screen identifies Cd74 as a common insertion site in murine B-lymphomas and reveals the existence of a novel IFNgamma-inducible Cd74 isoform

BACKGROUND

Insertional mutagenesis screens in the mouse are an acknowledged approach to identify genes involved in the pathogenesis of cancer. The potential of these screens to identify genes causally involved in tumorigenesis is not only limited to the murine host, but many of these genes have also been proven to be involved in the oncogenic process in man.

RESULTS

Through an insertional mutagenesis screen applying murine leukemia viruses in mouse, we found that Cd74 was targeted by proviral insertion in tumors of B-cell origin. This locus encodes a protein playing crucial roles in antigen presentation and B-cell homeostasis, and its deregulation is often associated with cancer in man. The distribution of insertions within the Cd74 locus prompted the identification of an alternative transcript initiated in intron 1 of Cd74 encoding an N-terminally truncated Cd74 isoform in tissues from un-infected mice, and transcriptional activation assays revealed a positive effect on the novel intronic promoter by a formerly described intronic enhancer in the Cd74 locus. Furthermore, we show that the new Cd74 isoform is IFNgamma inducible and that its expression is differentially regulated from the canonical Cd74 isoform at the transcriptional level.

CONCLUSIONS

We here identify Cd74 as a common insertion site in murine B-lymphomas and describe a novel IFNgamma-inducible murine Cd74 isoform differentially regulated from the canonical isoform and expressed under the control of an intronic promoter. The distribution and orientation of proviral insertion sites within the Cd74 locus underscores the causal involvement of the isoforms in the murine B-lymphomagenic process.

Mad3 negatively regulates B cell differentiation in the spleen by inducing Id2 expression

Immature B cells migrate to the spleen where they differentiate into mature cells. This final maturation step is crucial to enable B cells to become responsive to antigens and to participate in the immune response. Previously, we showed that Id2 acts as a negative regulator of the differentiation of immature B cells occurring in the spleen. Id2 expression has been found to depend on Myc-Max-Mad transcriptional complexes in mammary epithelial cells. Nearly all studies to date have shown that Mad proteins inhibit proliferation, presumably by antagonizing the function of Myc proteins. In the current study, we followed the Mad family members during peripheral B cell differentiation. We show that Mad3 actively regulates B cell differentiation. Our results demonstrate that high expression levels of Mad3 in immature B cells induce Id2 expression, which inhibits transcription of genes essential for B cell differentiation. During their differentiation to mature cells, B cells reduce their Mad3 expression, enabling the maturation process to occur.

TAp63 regulates VLA-4 expression and chronic lymphocytic leukemia cell migration to the bone marrow in a CD74-dependent manner

The hallmark of chronic lymphocytic leukemia (CLL) is the relentless accumulation of mature lymphocytes, mostly due to their decreased apoptosis. CD74 was recently shown to serve as a survival receptor on CLL cells. In this study, we show that stimulation of CD74 with its natural ligand, migration inhibitory factor, initiates a signaling cascade that results in upregulation of TAp63, which directly regulates CLL survival. In addition, TAp63 expression elevates the expression of the integrin VLA-4, particularly during the advanced stage of the disease. Blocking of CD74, TAp63, or VLA-4 inhibits the in vivo homing of CLL cells to the bone marrow (BM). Thus, CD74 and its target genes TAp63 and VLA-4 facilitate migration of CLL cells back to the BM, where they interact with the supportive BM environment that rescues them from apoptosis. These results could form the basis of novel therapeutic strategies aimed at blocking homing of CLL cells in their return to the BM and attenuating their survival.

Milatuzumab - a promising new immunotherapeutic agent

Milatuzumab is a new immunotherapeutic agent targeting CD74, a membrane protein preferentially expressed in hematopoietic cancers and some solid tumors. Broad expression and fast internalization makes CD74 an ideal target for cancer therapy. We reviewed published articles about CD74 and milatuzumab. We present a comprehensive review of CD74 functions and provide explanation of milatuzumab antitumor effects. This review describes CD74 protein biology with the emphasis on the role of CD74 in tumor survival and its new role in regulation of the Fas death receptor. The development of CD74 targeting therapies to induce tumor regression and cancer cell apoptosis is described and results of clinical trials are discussed. Milatuzumab shows selective binding and rapid internalization into CD74-positive cancer cells. Milatuzumab with and without conjugated toxins synergizes with other chemotherapeutic agents and elicits significant antitumor effects in mice. In a Phase I trial, milatuzumab showed no severe adverse effects in patients with relapsed/refractory multiple myeloma and it stabilized the disease in some patients for up to 12 weeks. Ongoing trials testing different treatment schedules of milatuzumab in chronic lymphocytic leukemia, non-Hodgkin's lymphoma and multiple myeloma indicate that milatuzumab shows no severe adverse effects in humans.

TATA-binding Protein (TBP)-like Protein Is Engaged in Etoposide-induced Apoptosis through Transcriptional Activation of Human TAp63 Gene

Accumulating evidence indicates that TBP (TATA-binding protein)-like protein (TLP) contributes to the regulation of stress-mediated cell cycle checkpoint and apoptotic pathways, although its physiological target genes have remained elusive. In the present study, we have demonstrated that human TAp63 is one of the direct transcriptional target genes of TLP. Enforced expression of TLP results in the transcriptional induction of the endogenous TAp63, but not of the other p53 family members such as TAp73 and p53. Consistent with these results, small interference RNA-mediated knockdown led to a significant down-regulation of the endogenous TAp63. Luciferase reporter assay and chromatin immunoprecipitation analysis revealed that the genomic region located at positions -487 to -29, where +1 represents the transcriptional initiation site of TAp63, is required for TLP-dependent transcriptional activation of TAp63 and also TLP is efficiently recruited onto this region. Additionally, cells treated with anti-cancer drug etoposide underwent apoptosis in association with the transcriptional enhancement of TAp63 in a p53-independent manner, and the knockdown of the endogenous TLP reduced etoposide-induced apoptosis through repression of TAp63 expression. Taken together, our present study identifies a TLP-TAp63 pathway that is further implicated in stress-induced apoptosis.

Isomer-specific effects of CLA on gene expression in human adipose tissue depending on PPARgamma2 P12A polymorphism: a double blind, randomized, controlled cross-over study

BACKGROUND

Peroxisome proliferator-activated receptor (PPAR)gamma is a key regulator in adipose tissue. The rare variant Pro12Ala of PPARgamma2 is associated with a decreased risk of insulin resistance. Being dietary PPARgamma ligands, conjugated linoleic acids (CLAs) received considerable attention because of their effects on body composition, cancer, atherosclerosis, diabetes, obesity and inflammation, although some effects were only demonstrated in animal trials and the results in human studies were not always consistent. In the present study effects of CLA supplementation on genome wide gene expression in adipose tissue biopsies from 11 Ala12Ala and 23 Pro12Pro men were investigated. Subjects underwent four intervention periods (4 wk) in a randomized double blind cross-over design receiving 4.25 g/d of either cis-9, trans-11 CLA, trans-10,cis-12 CLA, 1:1 mixture of both isomers or a reference linoleic acid oil preparation. After each intervention biopsies were taken, whole genome expression microarrays were applied, and genes of interest were verified by realtime PCR.

RESULTS

The following genes of lipid metabolism were regulated by CLA: LDLR, FASN, SCD, FADS1 and UCP2 were induced, while ABCA1, CD36 and CA3 were repressed. Transcription factors PPARgamma, NFAT5, CREB5 and EBF1, the adipokine NAMPT, members of the insulin signaling cascade SORBS1 and IGF1 and IL6ST were repressed, while the adipokine THBS1 and GLUT4 involved in insulin signaling were induced. Compared to trans-10,cis-12 CLA and the CLA mixture the cis-9, trans-11 CLA isomer exerted weaker effects. Only CD36 (-1.2 fold) and THBS1 (1.5 fold) were regulated. The CLA effect on expression of PPARgamma and leptin genes depends on the PPARgamma2 genotype.

CONCLUSION

The data suggest that the isomer specific influence of CLA on glucose and lipid metabolism is genotype dependent and at least in part mediated by PPARgamma.

TRIAL REGISTRATION

http://www.controlled-trials.com: ISRCTN91188075.

Mechanism of Fas signaling regulation by human herpesvirus 8 K1 oncoprotein

BACKGROUND

Herpesvirus 8 (HHV-8) oncoprotein K1 is linked to lymphoproliferation and suppression of apoptosis mediated by the Fas death receptor. Expression of K1 in transgenic mice induces accumulation of lymphoid tissue cells and lymphoma.

METHODS

To examine how K1 and Fas interact to suppress apoptosis, K1-Fas binding was studied in human embryonic kidney (HEK) and lymphoma (BJAB) cells that expressed wild-type K1 or a K1 Ig domain deletion mutant and were treated with Fas ligand (FasL) or an agonistic Fas antibody, using immunoprecipitation and Western blot analysis. Cleavage of caspase-3 and apoptosis was compared in liver samples from mice that were transfected with empty vector vs with plasmids expressing wild-type K1 or a K1 Ig deletion mutant and treated with agonistic Fas antibody for 7 hours. These studies used immunohistochemical staining and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay. All statistical tests were two-sided.

RESULTS

Immunoprecipitation and Western blot analysis of transfected HEK and BJAB cells revealed that wild-type K1 but not Ig-deleted K1 binds to Fas and prevents Fas activation by FasL or by an agonistic Fas antibody. More mice that were transfected with wild-type K1 (7 of 10) than mice transfected with empty vector (3 of 13) or the K1 Ig deletion mutant (0 of 6) survived treatment with the agonistic Fas antibody. Compared with vector-transfected mice, livers of wild-type K1-transfected mice contained fewer cells in which caspase-3 was cleaved (87.6% vs 58.0%, difference = 29.6%, 95% confidence interval [CI] = 19.2% to 40.0%; P = .003) and fewer apoptotic cells (83.7% vs 34.2%, difference = 49.5%, 95% CI = 39.8% to 59.2%; P = .003).

CONCLUSIONS

K1 blocks Fas signaling by directly binding to Fas through the Ig-like domain of K1 and preventing binding of FasL. The relative resistance of cancer cells to Fas-mediated apoptosis may be due to the inhibition of Fas by Ig domain-containing proteins.

Molecular subsets in the gene expression signatures of scleroderma skin

BACKGROUND

Scleroderma is a clinically heterogeneous disease with a complex phenotype. The disease is characterized by vascular dysfunction, tissue fibrosis, internal organ dysfunction, and immune dysfunction resulting in autoantibody production.

METHODOLOGY AND FINDINGS

We analyzed the genome-wide patterns of gene expression with DNA microarrays in skin biopsies from distinct scleroderma subsets including 17 patients with systemic sclerosis (SSc) with diffuse scleroderma (dSSc), 7 patients with SSc with limited scleroderma (lSSc), 3 patients with morphea, and 6 healthy controls. 61 skin biopsies were analyzed in a total of 75 microarray hybridizations. Analysis by hierarchical clustering demonstrates nearly identical patterns of gene expression in 17 out of 22 of the forearm and back skin pairs of SSc patients. Using this property of the gene expression, we selected a set of 'intrinsic' genes and analyzed the inherent data-driven groupings. Distinct patterns of gene expression separate patients with dSSc from those with lSSc and both are easily distinguished from normal controls. Our data show three distinct patient groups among the patients with dSSc and two groups among patients with lSSc. Each group can be distinguished by unique gene expression signatures indicative of proliferating cells, immune infiltrates and a fibrotic program. The intrinsic groups are statistically significant (p<0.001) and each has been mapped to clinical covariates of modified Rodnan skin score, interstitial lung disease, gastrointestinal involvement, digital ulcers, Raynaud's phenomenon and disease duration. We report a 177-gene signature that is associated with severity of skin disease in dSSc.

CONCLUSIONS AND SIGNIFICANCE

Genome-wide gene expression profiling of skin biopsies demonstrates that the heterogeneity in scleroderma can be measured quantitatively with DNA microarrays. The diversity in gene expression demonstrates multiple distinct gene expression programs in the skin of patients with scleroderma.

Tracking Differential Gene Expression in MRL/MpJ Versus C57BL/6 Anergic B Cells: Molecular Markers of Autoimmunity

Background

Anergy is a key mechanism controlling expression of autoreactive B cells and a major site for failed regulation in autoimmune diseases. Yet the molecular basis for this differentiated cell state remains poorly understood. The current lack of well-characterized surface or molecular markers hinders the isolation of anergic cells for further study. Global gene profiling recently identified transcripts whose expression differentiates anergic from naïve B cells in model mouse systems. The objective of the current study was to evaluate the molecular and cellular processes that differentiate anergic cells that develop in the healthy C57BL/6 (B6) milieu from those that develop in the autoimmune-prone MRL/MpJ (MRL) background. This approach takes advantage of B6 and MRL mice bearing an anti-laminin Ig transgene with a well characterized anergic B cell phenotype.

Results

Global gene expression was evaluated in purified transgenic B cells using Operon version 3.0 oligonucleotide microarray assaying >31,000 oligoprobes. Genes with a 2-fold expression difference in B6 as compared to MRL anergic B cells were identified. Expression of selected genes was confirmed using quantitative RT-PCR. This approach identified 43 probes corresponding to 37 characterized genes, including Ptpn22, CD74, Birc1f/Naip, and Ctla4, as differentially expressed in anergic B cells in the two strains. Gene Ontology classification identified differentiation, cell cycle, proliferation, development, apoptosis, and cell death as prominently represented ontology groups. Ingenuity Pathway Analysis identified two major networks incorporating 27 qualifying genes. Network 1 centers on beta-estradiol and TP53, and Network 2 encompasses RB1, p38 MAPK, and NFkB cell growth, proliferation, and cell cycle signaling pathways.

Conclusion

Using microarray analysis we identified 37 characterized genes and two functional pathways engaged in maintenance of B cell anergy for which expression is distorted by underlying autoimmune genetic susceptibility. This approach identifes a new biological role for multiple genes and potential new therapeutic targets in autoimmunity.

Perivascular clusters of dendritic cells provide critical survival signals to B cells in bone marrow niches

Beyond its established function in hematopoiesis, the bone marrow hosts mature lymphocytes and acts as a secondary lymphoid organ in the initiation of T cell and B cell responses. Here we report the characterization of bone marrow-resident dendritic cells (bmDCs). Multiphoton imaging showed that bmDCs were organized into perivascular clusters that enveloped blood vessels and were seeded with mature B lymphocytes and T lymphocytes. Conditional ablation of bmDCs in these bone marrow immune niches led to the specific loss of mature B cells, a phenotype that could be reversed by overexpression of the antiapoptotic factor Bcl-2 in B cells. The presence of bmDCs promoted the survival of recirculating B cells in the bone marrow through the production of macrophage migration-inhibitory factor. Thus, bmDCs are critical for the maintenance of recirculating B cells in the bone marrow.