A splice variant of CD99 increases motility and MMP-9 expression of human breast cancer cells through the AKT-, ERK-, and JNK-dependent AP-1 activation signaling pathways

Transcriptome Analysis Reveals the Induction of Apoptosis-Related Genes by a Monoclonal Antibody against a New Epitope of CD99 on T-Acute Lymphoblastic Leukemia

CD99 was demonstrated to be a potential target for antibody therapy on T-acute lymphoblastic leukemia (T-ALL). The ligation of CD99 by certain monoclonal antibodies (mAbs) induced T-ALL apoptosis. However, the molecular basis contributing to the apoptosis of T-ALL upon anti-CD99 mAb engagement remains elusive. In this study, using our generated anti-CD99 mAb clone MT99/3 (mAb MT99/3), mAb MT99/3 engagement strongly induced apoptosis of T-ALL cell lines, but not in non-malignant peripheral blood cells. By transcriptome analysis, upon mAb MT99/3 ligation, 13 apoptosis-related genes, including FOS, TNF, FASLG, BCL2A1, JUNB, SOCS1, IL27RA, PTPN6, PDGFA, NR4A1, SGK1, LPAR5 and LTB, were significantly upregulated. The epitope of CD99 recognized by mAb MT99/3 was then identified as the VDGENDDPRPP at residues 60-70 of CD99, which has never been reported. To the best of our knowledge, this is the first transcriptome data conducted in T-ALL with anti-CD99 mAb engagement. These findings provide new insights into CD99 implicated in the apoptosis of T-ALL. The identification of a new epitope and apoptosis-related genes that relate to the induction of apoptosis by mAb MT99/3 may serve as a new therapeutic target for T-ALL. The anti-CD99 mAb clone MT99/3 might be a candidate for further development of a therapeutic antibody for T-ALL therapy.

Porphyromonas gingivalis Gingipains Destroy the Vascular Barrier and Reduce CD99 and CD99L2 Expression To Regulate Transendothelial Migration

Porphyromonas gingivalis is an important periodontal pathogen that can cause vascular injury and invade local tissues through the blood circulation, and its ability to evade leukocyte killing is critical to its distal colonization and survival. Transendothelial migration (TEM) is a series of that enable leukocytes to squeeze through endothelial barriers and migrate into local tissues to perform immune functions. Several studies have shown that P. gingivalis-mediated endothelial damage initiates a series of proinflammatory signals that promote leukocyte adhesion. However, whether P. gingivalis is involved in TEM and thus influences immune cell recruitment remains unknown. In our study, we found that P. gingivalis gingipains could increase vascular permeability and promote Escherichia coli penetration by downregulating platelet/endothelial cell adhesion molecule 1 (PECAM-1) expression in vitro. Furthermore, we demonstrated that although P. gingivalis infection promoted monocyte adhesion, the TEM capacity of monocytes was substantially impaired, which might be due to the reduced CD99 and CD99L2 expression on gingipain-stimulated endothelial cells and leukocytes. Mechanistically, gingipains mediate CD99 and CD99L2 downregulation, possibly through the inhibition of the phosphoinositide 3-kinase (PI3K)/Akt pathway. In addition, our in vivo model confirmed the role of P. gingivalis in promoting vascular permeability and bacterial colonization in the liver, kidney, spleen, and lung and in downregulating PECAM-1, CD99, and CD99L2 expression in endothelial cells and leukocytes. IMPORTANCE P. gingivalis is associated with a variety of systemic diseases and colonizes in distal locations in the body. Here, we found that P. gingivalis gingipains degrade PECAM-1 to promote bacterial penetration while simultaneously reducing leukocyte TEM capacity. A similar phenomenon was also observed in a mouse model. These findings established P. gingivalis gingipains as the key virulence factor in modulating the permeability of the vascular barrier and TEM processes, which may provide a new rationale for the distal colonization of P. gingivalis and its associated systemic diseases.

CD99 in malignant hematopoiesis

The CD99 gene encodes a transmembrane protein that is involved in cell differentiation, adhesion, migration, and protein trafficking. CD99 is differentially expressed on the surface of hematopoietic cells both in the myeloid and lymphoid lineages. CD99 has two isoforms, the long and short isoforms that play different roles depending on the cellular context. There has been extensive evidence supporting the role of CD99 in myeloid and lymphoblastic leukemias. Here we review research findings related to the CD99 in malignant hematopoiesis. We also summarize the significance of CD99 as a therapeutic target in hematological malignancies.

MAP Kinase Phosphatase-5 Deficiency Protects Against Pressure Overload-Induced Cardiac Fibrosis

Cardiac fibrosis, a pathological condition due to excessive extracellular matrix (ECM) deposition in the myocardium, is associated with nearly all forms of heart disease. The processes and mechanisms that regulate cardiac fibrosis are not fully understood. In response to cardiac injury, macrophages undergo marked phenotypic and functional changes and act as crucial regulators of myocardial fibrotic remodeling. Here we show that the mitogen-activated protein kinase (MAPK) phosphatase-5 (MKP-5) in macrophages is involved in pressure overload-induced cardiac fibrosis. Cardiac pressure overload resulting from transverse aortic constriction (TAC) leads to the upregulation of Mkp-5 gene expression in the heart. In mice lacking MKP-5, p38 MAPK and JNK were hyperactivated in the heart, and TAC-induced cardiac hypertrophy and myocardial fibrosis were attenuated. MKP-5 deficiency upregulated the expression of the ECM-degrading matrix metalloproteinase-9 (Mmp-9) in the Ly6Clow (M2-type) cardiac macrophage subset. Consistent with in vivo findings, MKP-5 deficiency promoted MMP-9 expression and activity of pro-fibrotic macrophages in response to IL-4 stimulation. Furthermore, using pharmacological inhibitors against p38 MAPK, JNK, and ERK, we demonstrated that MKP-5 suppresses MMP-9 expression through a combined effect of p38 MAPK/JNK/ERK, which subsequently contributes to the inhibition of ECM-degrading activity. Taken together, our study indicates that pressure overload induces MKP-5 expression and facilitates cardiac hypertrophy and fibrosis. MKP-5 deficiency attenuates cardiac fibrosis through MAPK-mediated regulation of MMP-9 expression in Ly6Clow cardiac macrophages.

CD99 antibody disrupts T-cell acute lymphoblastic leukemia adhesion to meningeal cells and attenuates chemoresistance

Central nervous system (CNS) relapse is a significant cause of treatment failure among patients with acute lymphoblastic leukemia. In prior work we found that the meninges, the thin layer of tissue that covers the brain and spinal cord, harbor leukemia cells in the CNS. Importantly, direct interactions between leukemia and meningeal cells enabled leukemia chemoresistance. Herein, we show that an antibody targeting CD99, a transmembrane protein expressed on meningeal cells and many leukemia cells, disrupts adhesion between leukemia and meningeal cells and restores sensitivity of the leukemia cells to chemotherapy. This work identifies a mechanism regulating critical intercellular interactions within the CNS leukemia niche and may lead to novel therapeutic approaches for overcoming niche-mediated chemoresistance.

Clofarabine induces ERK/MSK/CREB activation through inhibiting CD99 on Ewing sarcoma cells

Clofarabine, an FDA approved purine analog, is used in the treatment of relapsed or refractory acute lymphoblastic leukemia. Clofarabine acts by inhibiting DNA synthesis. We demonstrated that clofarabine may have a novel function though inhibiting CD99, a transmembrane protein highly expressed on Ewing Sarcoma (ES) cells. CD99 is a validated target in ES whose inhibition may lead to a high therapeutic index for patients. Here we present additional data to support the hypothesis that clofarabine acts on CD99 and regulates key signaling pathways in ES. Cellular thermal shift assay indicated a direct interaction between clofarabine and CD99 in ES cell lysates. Clofarabine induced ES cell death does not require clofarabine's conversion to its active form by deoxycytidine kinase. A phosphokinase array screen with clofarabine and a CD99 blocking antibody identified alterations in signaling pathways. CD99 inhibition with clofarabine in ES cells caused rapid and sustained phosphorylation of ERK, MSK, and CREB. However, activation of this pathway did not correlate with clofarabine induced ES cell death. In summary, we demonstrated that clofarabine may activate ERK, MSK, and CREB phosphorylation through CD99 within minutes, however this paradoxical activation and subsequent ES cell death requires additional investigation.

Anti-human CD99 antibody exerts potent antitumor effects in mantle cell lymphoma

CD99 is a surface molecule expressed on various cell types including cancer cells. Expression of CD99 on multiple myeloma is associated with CCND1-IGH fusion/t(11;14). This translocation has been reported to be a genetic hallmark of mantle cell lymphoma (MCL). MCL is characterized by overexpression of cyclin D1 and high tumor proliferation. In this study, high expression of CD99 on MCL cell lines was confirmed. Our generated anti-CD99 monoclonal antibody (mAb), termed MT99/3, exerted potent antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) activities against mantle B-cell lymphoma without direct cytotoxic effects. The anti-tumor activities of mAb MT99/3 were more effective in MCL than in other B-cell lymphomas. Moreover, in a mouse xenograft model using Z138 MCL cell line, treatment of mAb MT99/3 reduced tumor development and growth. Our study indicated that mAb MT99/3 is a promising immunotherapeutic candidate for mantle cell lymphoma therapy.

RNA binding proteins: Linking mechanotransduction and tumor metastasis

Mechanotransduction is the leading cellular process that mammalian cells adopted to receive and respond to various mechanical cues from their local microenvironment. Increasing evidence suggests that mechano-transduction is involved in many physiological and disease conditions, ranging from early embryonic development, organogenesis, to a variety of human diseases including cancer. Mechanotransduction is mediated through several classes of senor proteins on the cell surface, intracellular signaling mediators, and core transcriptional regulation networks. Dissecting the molecular mechanisms regulating mechanotransduction and their association with cancer metastasis has received much attention in recent years. RNA binding proteins (RBPs) are a special group of nucleic acid interacting factors that participate in many important cellular processes. In this review, we would like to summarize recent research progresses in understanding the role of RBPs-mediated regulation in mechanotransduction and cancer metastasis. Those intriguing findings will provide novel insights for the disease and guide the potential development of new therapeutic approaches.

Identification and functional analysis of a novel splice variant of AC3-33 in breast cancer

Alternative RNA splicing plays a key role in regulating gene function and influencing protein expression diversity. In the present study, an AC-33 transcript variant (NCBI Reference Sequence: NM_001308229.1), splice variant (sv)AC3-33, was successfully cloned from the MCF-7 breast cancer cell line by reverse transcription PCR using primers based on expressed sequence tags. The aim of the present study was to investigate the structure and function of svAC3-33. svAC3-33 has an open reading frame of 1,825 base pairs, lacks AC3-33 exon 2 and is encoded by 294 amino acids. svAC3-33 is localized within the cytoplasm. The Cell Counting Kit-8 and EdU detection of cell proliferation assays showed that svAC3-33 inhibited MCF-7 cell proliferation. Similarly, svAC3-33 knockdown by RNA interference was shown to have the opposite effect by repressing the cell cycle progression of breast cancer cells. Furthermore, the data indicated that svAC3-33 may upregulate the expression of p21. The present study provides evidence that the increased expression of svAC3-33 may inhibit the activity of the transcription factor AP-1. The luciferase reporter gene assay detected a downregulation of the expression of c-Jun, but not c-Fos, which in turn affected cell proliferation. In conclusion, these results indicated a function for svAC3-33 in inhibiting the cell proliferation of MCF-7 cells by regulating the AP-1 signaling pathway.

Expression and Role of MicroRNA-663b in Childhood Acute Lymphocytic Leukemia and its Mechanism

Recent studies have shown that microRNAs (miRNAs) play a key role in various malignant tumors. MiR-663b has been found to have important roles in several cancers, however, the role of miR-663b in T cell acute lymphocytic leukemia (T-ALL) remains unclear. Therefore, we speculated that miR-663b might also play a crucial role in the development and process of T-ALL. In the present study, we found that miR-663b was up-regulated in the blood of children with T-ALL and T-ALL cell lines. TargetScan and dual luciferase reporter assay results showed that CD99 was a direct target of miR-663b. In order to further study the biological function of miR-663b in the development of T-ALL and to clarify its potential molecular mechanism, we detected the changes in proliferation, apoptosis, migration, and invasion of T-ALL cell line Jurkat before and after miR-663b inhibitor transfection. We found that miR-663b inhibitor inhibited Jurkat cell proliferation and induced apoptosis. In addition, miR-663b inhibitor repressed Jurkat cell migration and invasion. All these effects of miR-663b inhibitor on Jurkat cells were eliminated by CD99-silencing. These results have provided a new theoretical basis and strategy for the diagnosis and treatment of T-ALL.

CD73 complexes with emmprin to regulate MMP-2 production from co-cultured sarcoma cells and fibroblasts

Background

Interaction between cancer cells and fibroblasts mediated by extracellular matrix metalloproteinase inducer (emmprin, CD147) is important in the invasion and proliferation of cancer cells. However, the exact mechanism of emmprin mediated stimulation of matrix metalloprotease-2 (MMP-2) production from fibroblasts has not been elucidated. Our previous studies using an inhibitory peptide against emmprin suggested the presence of a molecule on the cell membrane which forms a complex with emmprin. Here we show that CD73 expressed on fibroblasts interacts with emmprin and is a required factor for MMP-2 production in co-cultures of sarcoma cells with fibroblasts.

Methods

CD73 along with CD99 was identified by mass spectrometry analysis as an emmprin interacting molecule from a co-culture of cancer cells (epithelioid sarcoma cell line FU-EPS-1) and fibroblasts (immortalized fibroblasts cell line ST353i). MMP-2 production was measured by immunoblot and ELISA. The formation of complexes of CD73 with emmprin was confirmed by immunoprecipitation, and their co-localization in tumor cells and fibroblasts was shown by fluorescent immunostaining and proximity ligation assays.

Results

Stimulated MMP-2 production in co-culture of cancer cells and fibroblasts was completely suppressed by siRNA knockdown of CD73, but not by CD99 knockdown. MMP-2 production was not suppressed by CD73-specific enzyme inhibitor (APCP). However, MMP-2 production was decreased by CD73 neutralizing antibodies, suggesting that CD73-mediated suppression of MMP-2 production is non-enzymatic. In human epithelioid sarcoma tissues, emmprin was immunohistochemically detected to be mainly expressed in tumor cells, and CD73 was expressed in fibroblasts and tumor cells: emmprin and CD73 were co-localized predominantly on tumor cells.

Conclusion

This study provides a novel insight into the role of CD73 in emmprin-mediated regulation of MMP-2 production.

Clinical and preclinical characterization of CD99 isoforms in acute myeloid leukemia

In an effort to identify target genes in acute myeloid leukemia (AML), we compared gene expression profiles between normal and AML cells from various publicly available datasets. We identified CD99, a gene that is up-regulated in AML patients. In 186 patients from The Cancer Genome Atlas AML dataset, CD99 was over-expressed in patients with FLT3-ITD and was down-regulated in patients with TP53 mutations. CD99 is a trans-membrane protein expressed on leukocytes and plays a role in cell adhesion, trans-endothelial migration, and T-cell differentiation. The CD99 gene encodes two isoforms with distinct expression and functional profiles in both normal and malignant tissues. Here we report that, although the CD99 long isoform initially induces an increase in cell proliferation, it also induces higher levels of reactive oxygen species, DNA damage, apoptosis and a subsequent decrease in cell viability. In several leukemia murine models, the CD99 long isoform delayed disease progression and resulted in lower leukemia engraftment in the bone marrow. Furthermore, the CD99 monoclonal antibody reduced cell viability, colony formation, and cell migration, and induced cell differentiation and apoptosis in leukemia cell lines and primary blasts. Mechanistically, CD99 long isoform resulted in transient induction followed by a dramatic decrease in both ERK and SRC phosphorylation. Altogether, our study provides new insights into the role of CD99 isoforms in AML that could potentially be relevant for the preclinical development of CD99 targeted therapy.

Dietary walnut altered gene expressions related to tumor growth, survival, and metastasis in breast cancer patients: a pilot clinical trial

Consumption of walnuts has slowed breast cancer growth and/or reduced the risk of mammary cancer in mice. The benefit against cancer was associated with altered expression of genes for cancer growth and survival. We hypothesized that walnut consumption would alter gene expression in pathologically confirmed breast cancers of women in a direction that would be expected to decrease breast cancer growth and survival, as was seen in mice. The study was a nonplacebo, 2-arm, clinical trial. Women with breast lumps large enough for research and pathology biopsies were recruited and randomized to walnut consuming or control groups. Immediately after biopsy collection, women in the walnut group began to consume 2 oz of walnuts per day until follow-up surgery. Pathological studies confirmed that lumps were breast cancer in all women who remained in the trial. At surgery, about 2 weeks after biopsy, additional specimens were taken from the breast cancers. Changes in gene expression in the surgical specimen compared to baseline were determined in each individual woman in walnut-consuming (n = 5) and control (n = 5) groups. RNA sequencing expression profiling revealed that expression of 456 identified genes was significantly changed in the tumor due to walnut consumption. Ingenuity Pathway Analysis showed activation of pathways that promote apoptosis and cell adhesion, and inhibition of pathways that promote cell proliferation and migration. These results support the hypothesis that, in humans, walnut consumption could suppress growth and survival of breast cancers.

CD99 Expression in Glioblastoma Molecular Subtypes and Role in Migration and Invasion

Glioblastoma (GBM) is the most aggressive type of brain tumor, with an overall survival of 17 months under the current standard of care therapy. CD99, an over-expressed transmembrane protein in several malignancies, has been considered a potential target for immunotherapy. To further understand this potentiality, we analyzed the differential expression of its two isoforms in human astrocytoma specimens, and the CD99 involved signaling pathways in glioma model U87MG cell line. CD99 was also analyzed in GBM molecular subtypes. Whole transcriptomes by RNA-Seq of CD99-siRNA, and functional in vitro assays in CD99-shRNA, that are found in U87MG cells, were performed. Astrocytoma of different malignant grades and U87MG cells only expressed CD99 isoform 1, which was higher in mesenchymal and classical than in proneural GBM subtypes. Genes related to actin dynamics, predominantly to focal adhesion, and lamellipodia/filopodia formation were down-regulated in the transcriptome analysis, when CD99 was silenced. A decrease in tumor cell migration/invasion, and dysfunction of focal adhesion, were observed in functional assays. In addition, a striking morphological change was detected in CD99-silenced U87MG cells, further corroborating CD99 involvement in actin cytoskeleton rearrangement. Inhibiting the overexpressed CD99 may improve resectability and decrease the recurrence rate of GBM by decreasing tumor cells migration and invasion.

RasGRF2 promotes migration and invasion of colorectal cancer cells by modulating expression of MMP9 through Src/Akt/NF-κB pathway

Ras-specific guanine nucleotide-releasing factor 2 (RasGRF2) is a member of the guanine nucleotide exchange factors family which is expressed in a variety of tissues and cancer. However, the role of RasGRF2 in cancer is less reported, especially in colorectal cancer(CRC). Hence, the present study aimed to investigated the function of RasGRF2 and ways in which it affects tumor progression in CRC samples and cell lines. We first measured RasGRF2 mRNA level in 26 paired tumor and nontumor colon tissues after colon cancer surgical resection, and determined RasGRF2 protein level in 97 paired paraffin-embedded colon cancer tissues, and found that levels of RasGRF2 mRNA and protein were increased in colorectal tumor tissues, compared with adjacent non-tumor tissues. We then examined the effects of RasGRF2 knockdown on proliferation, migration and invasion were analyzed in CRC cells (SW480, HCT116 and LS174T). HCT116 cells with RasGRF2 knockdown were injected into the tail vein in nude mice to yield metastatic model, and tumor metastasis was measured as well. We found that knockdown of RasGRF2 in CRC cells reduced their migration and invasion in vitro and metastasis in mice. Furthermore, we explored the underlying molecular mechanism for RasGRF2-mediated CRC migration and invasion. The results showed that knockdown of RasGRF2 in CRC cells impairing the expression of MMP9 and inhibiting the activation of Src/Akt and NF-κB signaling. We conclude that RasGRF2 plays a role in controlling migration and invasion of CRC and modulates the expression of MMP9 through Src/PI 3-kinase and the NF-κB pathways.

Combinatorial engineering of N-TIMP2 variants that selectively inhibit MMP9 and MMP14 function in the cell

Developing selective inhibitors for proteolytic enzymes that share high sequence homology and structural similarity is important for achieving high target affinity and functional specificity. Here, we used a combination of yeast surface display and dual-color selective library screening to obtain selective inhibitors for each of the matrix metalloproteinases (MMPs) MMP14 and MMP9 by modifying the non-specific N-terminal domain of the tissue inhibitor of metalloproteinase-2 (N-TIMP2). We generated inhibitor variants with 30- to 1175-fold improved specificity to each of the proteases, respectively, relative to wild type N-TIMP2. These biochemical results accurately predicted the selectivity and specificity obtained in cell-based assays. In U87MG cells, the activation of MMP2 by MMP14 was inhibited by MMP14-selective blockers but not MMP9-specific inhibitors. Target specificity was also demonstrated in MCF-7 cells stably expressing either MMP14 or MMP9, with only the MMP14-specific inhibitors preventing the mobility of MMP14-expressing cells. Similarly, the mobility of MMP9-expressing cells was inhibited by the MMP9-specific inhibitors, yet was not altered by the MMP14-specific inhibitors. The strategy developed in this study for improving the specificity of an otherwise broad-spectrum inhibitor will likely enhance our understanding of the basis for target specificity of inhibitors to proteolytic enzymes, in general, and to MMPs, in particular. We, moreover, envision that this study could serve as a platform for the development of next-generation, target-specific therapeutic agents. Finally, our methodology can be extended to other classes of proteolytic enzymes and other important target proteins.

Influence of transcriptional variants on metastasis

Cancer metastasis is defined as the dissemination of malignant cells from the primary tumor site, leading to colonization of distant organs and the establishment of a secondary tumor. Metastasis is frequently associated with chemoresistance and is the major cause of cancer-related mortality. Metastatic cells need to acquire the ability to resist to stresses provided by different environments, such as reactive oxygen species, shear stress, hemodynamic forces, stromal composition, and immune responses, to colonize other tissues. Hence, only a small population of cells has a metastasis-initiating potential. Several studies have revealed the misregulation of transcriptional variants during cancer progression, and many splice events can be used to distinguish between normal and tumoral tissue. These variants, which are abnormally expressed in malignant cells, contribute to an adaptive response of tumor cells and the success of the metastatic cascade, promoting an anomalous cell cycle, cellular adhesion, resistance to death, cell survival, migration and invasion. Understanding the different aspects of splicing regulation and the influence of transcriptional variants that control metastatic cells is critical for the development of therapeutic strategies. In this review, we describe how transcriptional variants contribute to metastatic competence and discuss how targeting specific isoforms may be a promising therapeutic strategy.

P2X7 receptor regulates EMMPRIN and MMP‑9 expression through AMPK/MAPK signaling in PMA‑induced macrophages

The rupture of atherosclerotic plaques may result in the formation of thrombi, which may induce subsequent cardiac events such as acute myocardial infarction. Overproduction of matrix metalloproteinases (MMPs) and extracellular matrix metalloproteinase inducers (EMMPRINs) by monocytes and macrophages may lead to rupture of atherosclerotic plaques as a result of the degradation of the extracellular matrix. The purinergic 2X7 receptor (P2X7R) is expressed in macrophages that are assembled in atherosclerotic lesions of human carotid arteries. P2X7R may serve a crucial role in the development of atherosclerosis; therefore, the present study aimed to determine whether P2X7R regulated the expression of EMMPRIN and MMP‑9 in phorbol 12‑myristate 13‑acetate (PMA)‑induced macrophages. In addition, the potential molecular mechanisms involved in this process were investigated. THP‑1 human monocytic cells were pretreated with A‑438079 (a specific inhibitor of P2X7R) for 1 h and subsequently incubated with or without PMA for 48 h. Exposure to A‑438079 significantly decreased the expression of MMP‑9 and EMMPRIN in the PMA‑induced macrophages and attenuated the activation (phosphorylation) of mitogen‑activated protein kinase (MAPK) signaling, including c‑Jun N‑terminal kinase, p38 and extracellular signal‑regulated kinase. The present study also demonstrated that 5'‑AMP‑activated protein kinase (AMPK) was activated by PMA exposure during differentiation from monocytes to macrophages. This activation was reversed by A‑438079 treatment through the inhibition of P2X7R expression. These results suggested that the inhibition of P2X7R may be able to suppress the AMPK/MAPK signaling pathway and consequently downregulate both EMMPRIN and MMP‑9 expression in PMA‑induced macrophages.

CD99: A Cell Surface Protein with an Oncojanus Role in Tumors

The cell surface molecule CD99 has gained interest because of its involvement in regulating cell differentiation and adhesion/migration of immune and tumor cells. However, the molecule plays an intriguing and dual role in different cell types. In particular, it acts as a requirement for cell malignancy or as an oncosuppressor in tumors. In addition, the gene encodes for two different isoforms, which also act in opposition inside the same cell. This review highlights key studies focusing on the dual role of CD99 and its isoforms and discusses major critical issues, challenges, and strategies for overcoming those challenges. The review specifically underscores the properties that make the molecule an attractive therapeutic target and identifies new relationships and areas of study that may be exploited. The elucidation of the spatial and temporal control of the expression of CD99 in normal and tumor cells is required to obtain a full appreciation of this molecule and its signaling.

CD99 at the crossroads of physiology and pathology

CD99 is a cell surface protein with unique features and only partly defined mechanisms of action. This molecule is involved in crucial biological processes, including cell adhesion, migration, death, differentiation and diapedesis, and it influences processes associated with inflammation, immune responses and cancer. CD99 is frequently overexpressed in many types of tumors, particularly pediatric tumors including Ewing sarcoma and specific subtypes of leukemia. Engagement of CD99 induces the death of malignant cells through non-conventional mechanisms. In Ewing sarcoma, triggering of CD99 by specific monoclonal antibodies activates hyperstimulation of micropinocytosis and leads to cancer cells killing through a caspase-independent, non-apoptotic pathway resembling methuosis. This process is characterized by extreme accumulation of vacuoles in the cytoplasmic space, which compromises cell viability, requires the activation of RAS-Rac1 downstream signaling and appears to be rather specific for tumor cells. In addition, anti-CD99 monoclonal antibodies exhibit antitumor activities in xenografts in the absence of immune effector cells or complement proteins. Overall, these data establish CD99 as a new opportunity to treat patients with high expression of CD99, particularly those that are resistant to canonical apoptosis-inducing agents.

CD99-Derived Agonist Ligands Inhibit Fibronectin-Induced Activation of β1 Integrin through the Protein Kinase A/SHP2/Extracellular Signal-Regulated Kinase/PTPN12/Focal Adhesion Kinase Signaling Pathway

The human CD99 protein is a 32-kDa glycosylated transmembrane protein that regulates various cellular responses, including cell adhesion and leukocyte extravasation. We previously reported that CD99 activation suppresses β1 integrin activity through dephosphorylation of focal adhesion kinase (FAK) at Y397. We explored a molecular mechanism underlying the suppression of β1 integrin activity by CD99 agonists and its relevance to tumor growth in vivo CD99-Fc fusion proteins or a series of CD99-derived peptides suppressed β1 integrin activity by specifically interacting with three conserved motifs of the CD99 extracellular domain. CD99CRIII3, a representative CD99-derived 3-mer peptide, facilitated protein kinase A-SHP2 interaction and subsequent activation of the HRAS/RAF1/MEK/ERK signaling pathway. Subsequently, CD99CRIII3 induced FAK phosphorylation at S910, which led to the recruitment of PTPN12 and PIN1 to FAK, followed by FAK dephosphorylation at Y397. Taken together, these results indicate that CD99-derived agonist ligands inhibit fibronectin-mediated β1 integrin activation through the SHP2/ERK/PTPN12/FAK signaling pathway.

Promoter CpG-Site Methylation of the KAI1 Metastasis Suppressor Gene Contributes to Its Epigenetic Repression in Prostate Cancer

BACKGROUND

Repression of the KAI1 metastasis suppressor gene is closely associated with malignancy and poor prognosis in many human cancer types including prostate cancer. Since gene repression in human cancers frequently results from epigenetic alterations by DNA methylation and histone modifications, we examined whether the KAI1 gene becomes silenced through these epigenetic mechanisms in prostate cancer.

METHODS

KAI1 mRNA and protein levels were determined by RT-PCR and immunoblotting analyses, respectively. Methylation status of the KAI1 promoter DNA in prostate cancer cell lines and tissues was evaluated by methylation-specific PCR analysis of bisulfite-modified genomic DNAs. Methylated CpG sites in the KAI1 promoter were identified by sequencing the PCR clones of the bisulfite-modified KAI1 promoter DNA. KAI1 protein levels in human prostate cancer tissue samples were examined by immunofluorescence staining of the tissues with an anti-KAI1 antibody.

RESULTS

Among the three human prostate cancer cell lines examined, PC3 and DU145 cells exhibited markedly decreased levels of KAI1 mRNA and protein as compared to LNCaP cells, even though the exogenous KAI1 promoter not being methylated was normally functional in all these cell lines. Treatment of the low KAI1-expressing cell lines with a demethylating agent, 5'-aza-2'-deoxycytidine, significantly elevated KAI1 expression levels, implicating the involvement of DNA methylation in KAI1 downregulation. Methylation of CpG islands within the KAI1 promoter region was observed in the low KAI1-expressing cells, but not in the high KAI1-expressing cells. Also, methyl CpG-binding proteins such as MBD2 and MeCP2 were complexed to the KAI1 promoter in the low KAI1-expressing cells. Bisulfite sequencing analysis identified the intensively methylated CpG residues in the KAI1 promoter clones derived from prostate cancer cells and tissues with no or low KAI1 expression. As in prostate cancer cell lines, prostate cancer tissues from patients also displayed a negative association between KAI1 expression levels and methylation status of the KAI1 promoter.

CONCLUSIONS

The present data suggest that the KAI1 gene might be repressed by epigenetic alterations through the promoter CpG-site methylation during prostate cancer progression. This epigenetic mechanism could provide a clue for understanding how the KAI1 gene was silenced in metastatic prostate cancers. Prostate 77: 350-360, 2017. © 2016 Wiley Periodicals, Inc.

Tissue transglutaminase-2 promotes gastric cancer progression via the ERK1/2 pathway

Gastric cancer (GC) is one of the most common tumors worldwide and involves extensive local tumor invasion, metastasis, and poor prognosis. Understanding mechanisms regulating progression of GC is necessary for developing effective therapeutic strategies. Tissue transglutaminase-2 (TG2), a multifunctional member of the transglutaminase family, has been shown to be critical for tumor initiation and progression. However, how TG2 promotes the progression of GC is unknown. We report that TG2 was highly expressed in GC tissues and positively associated with depth of tumor invasion and late TNM stage. With gain- and loss-of-function approaches, we observed that TG2 promoted GC cell proliferation, migration, invasion, as well as tumorigenesis and peritoneal metastasis in vivo. These events were associated with the ERK1/2 pathway activation and an ERK1/2 inhibitor (U0126) inhibited cell proliferation, migration, and invasion induced by overexpression of TG2. In summary, TG2 contributes to tumorigenesis and progression of GC by activating the ERK1/2 signaling pathway and is a potential therapeutic target of metastatic gastric cancer.

Dissecting cellular senescence and SASP in Drosophila

Cellular senescence can act as both tumor suppressor and tumor promoter depending on the cellular contexts. On one hand, premature senescence has been considered as an innate host defense mechanism against carcinogenesis in mammals. In response to various stresses including oxidative stress, DNA damage, and oncogenic stress, suffered cells undergo irreversible cell cycle arrest, leading to tumor suppression. On the other hand, recent studies in mammalian systems have revealed that senescent cells can drive oncogenesis by secreting diverse proteins such as inflammatory cytokines, matrix remodeling factors, and growth factors, the phenomenon called senescence-associated secretory phenotype (SASP). However, the mechanisms by which these contradictory effects regulate tumor growth and metastasis in vivo have been elusive. Here, we review the recent discovery of cellular senescence in Drosophila and the mechanisms underlying senescence-mediated tumor regulation dissected by Drosophila genetics.

Hsa-miR-623 suppresses tumor progression in human lung adenocarcinoma

Our previous study revealed that Ku80 was overexpressed in lung cancer tissues and hsa-miR-623 regulated the Ku80 expression; however, the detailed function of hsa-miR-623 in lung cancer was unclear. We identified that hsa-miR-623 bound to the 3'-UTR of Ku80 mRNA, thus significantly decreasing Ku80 expression in lung adenocarcinoma cells. Hsa-miR-623 was downregulated in lung adenocarcinoma tissues compared with corresponding non-tumorous tissues, and its expression was inversely correlated with Ku80 upregulation. Downregulation of hsa-miR-623 was associated with poor clinical outcomes of lung adenocarcinoma patients. Hsa-miR-623 suppressed lung adenocarcinoma cell proliferation, clonogenicity, migration and invasion in vitro. Hsa-miR-623 inhibited xenografts growth and metastasis of lung adenocarcinoma in vivo. Ku80 knockdown in lung adenocarcinoma cells suppressed tumor properties in vitro and in vivo similar to hsa-miR-623 overexpression. Further, hsa-miR-623 overexpression decreased matrix metalloproteinase-2 (MMP-2) and MMP-9 expression levels, with decreased ERK/JNK phosphorylation. Inhibition of hsa-miR-623 or overexpression of Ku80 promoted lung adenocarcinoma cell invasion, activated ERK/JNK phosphorylation and increased MMP-2/9 expressions, which could be reversed by ERK kinase inhibitor or JNK kinase inhibitor. In summary, our results showed that hsa-miR-623 was downregulated in lung adenocarcinoma and suppressed the invasion and metastasis targeting Ku80 through ERK/JNK inactivation mediated downregulation of MMP-2/9. These findings reveal that hsa-miR-623 may serve as an important therapeutic target in lung cancer therapy.

SPAG9 is overexpressed in osteosarcoma, and regulates cell proliferation and invasion through regulation of JunD

Sperm-associated antigen 9 (SPAG9) is a recently characterized oncoprotein that is considered to be involved in several forms of malignant tumor. However, its biological function and expression pattern in human osteosarcoma have not yet been elucidated. In the present study, SPAG9 expression was analyzed in 58 cases of human osteosarcoma by immunohistochemistry. The results demonstrated that SPAG9 was overexpressed in 63.8% (37/58) of osteosarcoma tissues, while normal bone tissues exhibited negative SPAG9 expression. SPAG9 small interfering RNA was employed in the U2OS cell line, which has high endogenous expression, and SPAG9 transfection was performed in the MG63 cell line, which has low endogenous expression. MTT and Matrigel invasion assays demonstrated that SPAG-9-knockdown significantly reduced U2OS cell invasion and proliferation, while SPAG9 transfection enhanced MG63 cell proliferation and invasion. Furthermore, it was observed that SPAG9 positively regulated cyclin D1, phosphorylated-c-Jun NH2-terminal kinase (JNK) and JunD expression. Treatment with the JNK inhibitor, SP600125, abolished the upregulatory effect of SPAG9 on JunD. Taken together, the present study identified SPAG9 as a critical oncoprotein involved in osteosarcoma proliferation and invasion, possibly functioning through JNK-JunD signaling.

Nonstructural 3 Protein of Hepatitis C Virus Modulates the Tribbles Homolog 3/Akt Signaling Pathway for Persistent Viral Infection

Hepatitis C virus (HCV) infection often causes chronic hepatitis, liver cirrhosis, and ultimately hepatocellular carcinoma. However, the mechanisms underlying HCV-induced liver pathogenesis are still not fully understood. By transcriptome sequencing (RNA-Seq) analysis, we recently identified host genes that were significantly differentially expressed in cell culture-grown HCV (HCVcc)-infected cells. Of these, tribbles homolog 3 (TRIB3) was selected for further characterization. TRIB3 was initially identified as a binding partner of protein kinase B (also known as Akt). TRIB3 blocks the phosphorylation of Akt and induces apoptosis under endoplasmic reticulum (ER) stress conditions. HCV has been shown to enhance Akt phosphorylation for its own propagation. In the present study, we demonstrated that both mRNA and protein levels of TRIB3 were increased in the context of HCV replication. We further showed that promoter activity of TRIB3 was increased by HCV-induced ER stress. Silencing of TRIB3 resulted in increased RNA and protein levels of HCV, whereas overexpression of TRIB3 decreased HCV replication. By employing an HCV pseudoparticle entry assay, we further showed that TRIB3 was a negative host factor involved in HCV entry. Both in vitro binding and immunoprecipitation assays demonstrated that HCV NS3 specifically interacted with TRIB3. Consequently, the association of TRIB3 and Akt was disrupted by HCV NS3, and thus, TRIB3-Akt signaling was impaired in HCV-infected cells. Moreover, HCV modulated TRIB3 to promote extracellular signal-regulated kinase (ERK) phosphorylation, activator protein 1 (AP-1) activity, and cell migration. Collectively, these data indicate that HCV exploits the TRIB3-Akt signaling pathway to promote persistent viral infection and may contribute to HCV-mediated pathogenesis.

IMPORTANCE

TRIB3 is a pseudokinase protein that acts as an adaptor in signaling pathways for important cellular processes. So far, the functional involvement of TRIB3 in virus-infected cells has not yet been demonstrated. We showed that both mRNA and protein expression levels of TRIB3 were increased in the context of HCV RNA replication. Gene silencing of TRIB3 increased HCV RNA and protein levels, and thus, overexpression of TRIB3 decreased HCV replication. TRIB3 is known to promote apoptosis by negatively regulating the Akt signaling pathway under ER stress conditions. Most importantly, we demonstrated that the TRIB3-Akt signaling pathway was disrupted by NS3 in HCV-infected cells. These data provide evidence that HCV modulates the TRIB3-Akt signaling pathway to establish persistent viral infection.

CD99 isoforms regulate CD1a expression in human monocyte-derived DCs through ATF-2/CREB-1 phosphorylation

CD1a expression is considered one of the major characteristics qualifying in vitro human dendritic cells (DCs) during their generation process. Here, we report that CD1A transcription is regulated by a mechanism involving the long and short isoforms of CD99. Using a lentiviral construct encoding for a CD99 short hairpin RNA, we were able to inhibit CD99 expression in human primary DCs. In such cells, CD1a membrane expression increased and CD1A transcripts were much higher in abundance compared to cells expressing CD99 long form (CD99LF). We also show that CD1A transcription is accompanied by a switch in expression from CD99LF to expression at comparable levels of both CD99 isoforms during immature DCs generation in vitro. We demonstrate that CD99LF maintains a lower level of CD1A transcription by up-regulating the phosphorylated form of the ATF-2 transcription factor and that CD99 short form (SF) is required to counteract this regulatory mechanism. Elucidation of the molecular mechanisms related to CD99 alternative splicing will be very helpful to better understand the transcriptional regulatory mechanism of CD1a molecules during DCs differentiation and its involvement in the immune response.

Investigational therapies for Ewing sarcoma: a search without a clear finding

INTRODUCTION

Ewing sarcoma family tumors (ESFT) are a group of aggressive diseases, characterized histologically by small, round, blue cells and genetically by translocation involving EWS and ETS partner genes. The current treatment of localized Ewing sarcoma (ES) requires a multi-disciplinary approach, including multidrug chemotherapy, administrated before and after local treatment, surgery and radiation therapy. Unfortunately, the cure rate of metastatic or refractory/recurrent disease is still very poor.

AREAS COVERED

In this review, the authors summarize the new types of therapy and strategies aimed to improve the prognosis or cure ES. Herein, the authors discuss several preclinical and phase I-II studies with new-targeted therapies. The most studied therapies are insulin-like growth factor receptor (IGF1R) inhibitors but have limited efficacy. Other strategies include Mammalian Target of Rapamycin (mTOR) Inhibition, poly ADP ribose polymerase (PARP) inhibition, vascular endothelial growth factor (VEGF) inhibition, tyrosine kinase inhibitors and telomerase inhibitors, all with limited effectiveness.

EXPERT OPINION

Future treatment strategies should combine one or more targeted therapies with conventional chemotherapy. Some combined modality treatments are under clinical study. However, treatment breakthroughs are still needed to improve the relatively poor prognosis of recurrent/metastatic ESFT.

CD99 regulates CXCL12-induced chemotaxis of human plasma cells

Migration of plasma cells (PCs) is crucial for the control of PC survival and antibody production and is controlled by chemokines, most importantly by CXCL12. This study investigated the role of CD99 in CXCL12-induced PC migration. Among B cell subsets in the tonsils, CD99 expression was highest in PCs. CD99 expression increased during in vitro differentiation of germinal center B cells and was highest in PCs. CD99 engagement reduced chemotactic migration of PCs toward CXCL12 and reduced extracellular signal-regulated kinase (ERK) activation by CXCL12. An ERK inhibitor reduced CXCL12-mediated chemotactic migration, which suggests that ERK has a critical role in migration. CD99 engagement did not influence apoptosis, differentiation, or antibody secretion of PCs. We propose a novel role of CD99 in PCs that suppresses ERK activation and chemotactic migration of these cells.

Engagement of CD99 Reduces AP-1 Activity by Inducing BATF in the Human Multiple Myeloma Cell Line RPMI8226

CD99 signaling is crucial to a diverse range of biological functions including survival and proliferation. CD99 engagement is reported to augment activator protein-1 (AP-1) activity through mitogen-activated protein (MAP) kinase pathways in a T-lymphoblastic lymphoma cell line Jurkat and in breast cancer cell lines. In this study, we report that CD99 differentially regulated AP-1 activity in the human myeloma cell line RPMI8226. CD99 was highly expressed and the CD99 engagement led to activation of the MAP kinases, but suppressed AP-1 activity by inducing the expression of basic leucine zipper transcription factor, ATF-like (BATF), a negative regulator of AP-1 in RPMI8226 cells. By contrast, engagement of CD99 enhanced AP-1 activity and did not change the BATF expression in Jurkat cells. CD99 engagement reduced the proliferation of RPMI8226 cells and expression of cyclin 1 and 3. Overall, these results suggest novel CD99 functions in RPMI8226 cells.

miR-181b as a therapeutic agent for chronic lymphocytic leukemia in the Eµ-TCL1 mouse model

The involvement of microRNAs (miRNAs) in chronic lymphocytic leukemia (CLL) pathogenesis suggests the possibility of anti-CLL therapeutic approaches based on miRNAs. Here, we used the Eµ-TCL1 transgenic mouse model, which reproduces leukemia with a similar course and distinct immunophenotype as human B-CLL, to test miR-181b as a therapeutic agent.In vitro enforced expression of miR-181b mimics induced significant apoptotic effects in human B-cell lines (RAJI, EHEB), as well as in mouse Eµ-TCL1 leukemic splenocytes. Molecular analyses revealed that miR-181b not only affected the expression of TCL1, Bcl2 and Mcl1 anti-apoptotic proteins, but also reduced the levels of Akt and phospho-Erk1/2. Notably, a siRNA anti-TCL1 could similarly down-modulate TCL1, but exhibited a reduced or absent activity in other relevant proteins, as well as a reduced effect on cell apoptosis and viability. In vivo studies demonstrated the capability of miR-181b to reduce leukemic cell expansion and to increase survival of treated mice.These data indicate that miR-181b exerts a broad range of actions, affecting proliferative, survival and apoptotic pathways, both in mice and human cells, and can potentially be used to reduce expansion of B-CLL leukemic cells.

CD99 inhibits CD98-mediated β1 integrin signaling through SHP2-mediated FAK dephosphorylation

The human CD99 protein is a 32-kDa type I transmembrane glycoprotein, while CD98 is a disulfide-linked 125-kDa heterodimeric type II transmembrane glycoprotein. It has been previously shown that CD99 and CD98 oppositely regulate β1 integrin signaling, though the mechanisms by which this regulation occurs are not known. Our results revealed that antibody-mediated crosslinking of CD98 induced FAK phosphorylation at Y397 and facilitated the formation of the protein kinase Cα (PKCα)-syntenin-focal adhesion kinase (FAK), focal adhesions (FAs), and IPP-Akt1-syntenin complex, which mediates β1 integrin signaling. In contrast, crosslinking of CD99 disrupted the formation of the PKCα-syntenin-FAK complex as well as FA via FAK dephosphorylation. The CD99-induced dephosphorylation of FAK was apparently mediated by the recruitment of Src homology region 2 domain-containing phosphatase-2 (SHP2) to the plasma membrane and subsequent activation of its phosphatase activity. Further consequences of the activation of SHP2 included the disruption of FAK-talin and talin-β1 integrin interactions and attenuation in the formation of the IPP-Akt1-syntenin complex at the plasma membrane, which resulted in reduced cell-ECM adhesion. This report uncovers the molecular mechanisms underlying the inverse regulation of β1 integrin signaling by CD99 and CD98 and may provide a novel therapeutic approach to treat inflammation and cancer.

Human myeloma cell lines induce osteoblast downregulation of CD99 which is involved in osteoblast formation and activity

CD99 is a transmembrane glycoprotein expressed in physiological conditions by cells of different tissues, including osteoblasts (OBs). High or low CD99 levels have been detected in various pathological conditions, and the supernatant of some carcinoma cell lines can modulate CD99 expression in OB-like cells. In the present work we demonstrate for the first time that two different human myeloma cell lines (H929 and U266) and, in a less degree, their conditioned media significantly downregulate CD99 expression in normal human OBs during the differentiation process. In the same experimental conditions the OBs display a less differentiated phenotype as demonstrated by the decreased expression of RUNX2 and Collagen I. On the contrary, when CD99 was activated by using a specific agonist antibody, the OBs become more active as demonstrated by the upregulation of Alkaline Phosphatase, Collagen I, RUNX2, and JUND expression. Furthermore, we demonstrate that the activation of CD99 is able to induce the phosphorylation of ERK 1/2 and AKT intracellular signal transduction molecules in the OBs.

Glycyrrhetinic acid potently suppresses breast cancer invasion and metastasis by impairing the p38 MAPK-AP1 signaling axis

INTRODUCTION

Radix Glycyrrhiza has been used in China for thousand years to treat cancer. However, focus on its tumor-suppressing mechanism has been concentrated on its effect on tumor cell growth and apoptosis.

OBJECTIVES

With the aid of a panel of human breast cancer cell lines, we reveal that glycyrrhetinic acid (GA), a major component of Radix Glycyrrhiza, is actually a significantly more potent agent to suppress invasion than cell survival.

RESULTS

GA effectively inhibits breast cancer cell MMP-2/MMP-9 expression; GA-induced reduction in the MMP-2/9 expression is apparently mediated by GA's ability to specifically inhibit the p38 MAPK activity and its downstream AP1 activation. Moreover, we show that GA down regulates the levels of Fra-1 and c-Jun, two main components of AP1 transcription complex in invasive breast cancer cells and that AP1-specific inhibitor abrogates breast cancer cell invasion. These results suggest that GA impairs the p38 MAPK-AP1 signaling axis, leading to the repression of breast cancer cell invasion. Finally, we demonstrate that GA effectively suppresses breast tumor outgrowth and pulmonary metastasis without causing animal weight loss or eliciting liver/kidney toxicity to the recipient animals.

CONCLUSION

This study indicates that GA represents a good candidate compound for the potential development of therapeutic drug.

EGCG inhibits proliferation, invasiveness and tumor growth by up-regulation of adhesion molecules, suppression of gelatinases activity, and induction of apoptosis in nasopharyngeal carcinoma cells

(-)-Epigallocatechin-3-gallate (EGCG), a major green tea polyphenol, has been shown to inhibit the proliferation of a variety of tumor cells. Epidemiological studies have shown that drinking green tea can reduce the incidence of nasopharyngeal carcinoma (NPC), yet the underlying mechanism is not well understood. In this study, the inhibitory effect of EGCG was tested on a set of Epstein Barr virus-negative and -positive NPC cell lines. Treatment with EGCG inhibited the proliferation of NPC cells but did not affect the growth of a non-malignant nasopharyngeal cell line, NP460hTert. Moreover, EGCG treated cells had reduced migration and invasive properties. The expression of the cell adhesion molecules E-cadherin and β-catenin was found to be up-regulated by EGCG treatment, while the down-regulation of matrix metalloproteinases (MMP)-2 and MMP-9 were found to be mediated by suppression of extracellular signal-regulated kinase (ERK) phosphorylation and AP-1 and Sp1 transactivation. Spheroid formation by NPC cells in suspension was significantly inhibited by EGCG. Oral administration of EGCG was capable of suppressing tumor growth in xenografted mice bearing NPC tumors. Treatment with EGCG was found to elevate the expression of p53 and p21, and eventually led to apoptosis of NPC cells via caspase 3 activation. The nuclear translocation of NF-κB and β-catenin was also suppressed by EGCG treatment. These results indicate that EGCG can inhibit the proliferation and invasiveness, and induce apoptosis, of NPC cells, making it a promising agent for chemoprevention or adjuvant therapy of NPC.

Curcumin inhibits EMMPRIN and MMP-9 expression through AMPK-MAPK and PKC signaling in PMA induced macrophages

In coronary arteries, plaque disruption, the major acute clinical manifestations of atherosclerosis, leads to a subsequent cardiac event, such as acute myocardial infarction (AMI) and unstable angina pectoris (UA). Numerous reports have shown that high expression of MMP-9 (matrix metalloproteinase-9), MMP-13 (matrix metalloproteinase-13) and EMMPRIN (extracellular matrix metalloproteinase induce) in monocyte/macrophage results in the plaque progression and destabilization. Curcumin exerts well-known anti-inflammatory and antioxidant effects and probably has a protective role in the atherosclerosis. The purpose of our study was to investigate the molecular mechanisms by which curcumin affects MMP-9, MMP13 and EMMPRIN in PMA (phorbol 12-myristate 13-acetate) induced macrophages. Human monocytic cells (THP-1 cells) were pretreated with curcumin or compound C for 1 h, and then induced by PMA for 48 h. Total RNA and proteins were collected for real-time PCR and Western blot analysis, respectively. In the present study, the exposure to curcumin resulted in attenuated JNK, p38, and ERK activation and decreased expression of MMP-9, MMP-13 and EMMPRIN in PMA induced macrophages. Moreover, we demonstrated that AMPK (AMP-activated protein kinase) and PKC (Protein Kinase C) was activated by PMA during monocyte/macrophage differentiation. Furthermore, curcumin reversed PMA stimulated PKC activation and suppressed the chronic activation of AMPK, which in turn reduced the expression of MMP-9, MMP-13 and EMMPRIN. Therefore, it is suggested that curcumin by inhibiting AMPK-MAPK (mitogen activated protein kinase) and PKC pathway may led to down-regulated EMMPRIN, MMP-9 and MMP-13 expression in PMA-induced THP-1 cells.

Genetics of breast cancer bone metastasis: a sequential multistep pattern

Bone metastasis accounts for the vast majority of breast cancer (BC) metastases, and is related to a high rate of morbidity and mortality. A number of seminal studies have uncovered gene expression signatures involved in BC development and bone metastasis; each of them points at a distinct step of the 'invasion-metastasis cascade'. In this review, we provide most recently discovered functions of sets of genes that are selected from widely accepted gene signatures that are implicate in BC progression and bone metastasis. We propose a possible sequential pattern of gene expression that may lead a benign primary breast tumor to get aggressiveness and progress toward bone metastasis. A panel of genes which primarily deal with features like DNA replication, survival, proliferation, then, angiogenesis, migration, and invasion has been identified. TGF-β, FGF, NFκB, WNT, PI3K, and JAK-STAT signaling pathways, as the key pathways involved in breast cancer development and metastasis, are evidently regulated by several genes in all three signatures. Epithelial to mesenchymal transition that is also an important mechanism in cancer stem cell generation and metastasis is evidently regulated by these genes. This review provides a comprehensive insight regarding breast cancer bone metastasis that may lead to a better understanding of the disease and take step toward better treatments.

Regulation of human CYP2C9 expression by electrophilic stress involves activator protein 1 activation and DNA looping

Cytochrome P450 (CYP)2C9 and CYP2C19 are important human enzymes that metabolize therapeutic drugs, environmental chemicals, and physiologically important endogenous compounds. Initial studies using primary human hepatocytes showed induction of both the CYP2C9 and CYP2C19 genes by tert-butylhydroquinone (tBHQ). As a pro-oxidant, tBHQ regulates the expression of cytoprotective genes by activation of redox-sensing transcription factors, such as the nuclear factor E2-related factor 2 (Nrf2) and members of the activator protein 1 (AP-1) family of proteins. The promoter region of CYP2C9 contains two putative AP-1 sites (TGAGTCA) at positions -2201 and -1930, which are also highly conserved in CYP2C19. The CYP2C9 promoter is activated by ectopic expression of cFos and JunD, whereas Nrf2 had no effect. Using specific kinase inhibitors for mitogen-activated protein kinase, we showed that extracellular signal-regulated kinase and Jun N-terminal kinase are essential for tBHQ-induced expression of CYP2C9. Electrophoretic mobility shift assays demonstrate that cFos distinctly interacts with the distal AP-1 site and JunD with the proximal site. Because cFos regulates target genes as heterodimers with Jun proteins, we hypothesized that DNA looping might be required to bring the distal and proximal AP-1 sites together to activate the CYP2C9 promoter. Chromosome conformation capture analyses confirmed the formation of a DNA loop in the CYP2C9 promoter, possibly allowing interaction between cFos at the distal site and JunD at the proximal site to activate CYP2C9 transcription in response to electrophiles. These results indicate that oxidative stress generated by exposure to electrophilic xenobiotics and metabolites induces the expression of CYP2C9 and CYP2C19 in human hepatocytes.

Downregulation of CD99 and upregulation of human leukocyte antigen class II promote tumor aggravation and poor survival in patients with osteosarcomas

BACKGROUND

CD99 is involved in the intracellular transport of human leukocyte antigen class II (HLA-II) protein. The aim of this study was to clarify the clinical value of CD99 and HLA-II expression in primary osteosarcoma.

METHODS

One hundred and thirty pairs of osteosarcoma and matched noncancerous bone tissues were evaluated by immunohistochemistry for CD99 and HLA-II expression.

RESULTS

Compared with the noncancerous bone tissues, the expression levels of CD99 (tumor versus normal: 2.96±0.09 versus 5.89±1.26, P<0.001) and HLA-II (tumor versus normal: 5.01±1.39 versus 1.92±0.06, P<0.001) proteins were respectively downregulated and upregulated in osteosarcoma tissues. CD99 and HLA-II were highly expressed in 49/130 (37.69%) and 107/130 (82.31%) of osteosarcoma tissues, respectively. In addition, the osteosarcoma patients with downregulation of CD99 and upregulation of HLA-II more frequently showed the presence of metastasis and recurrence and poor response to chemotherapy. Moreover, there was a negative correlation between CD99 and HLA-II expression in osteosarcoma tissues (r=-0.69, P=0.01). The patients with low CD99 expression correlated with poor prognosis of osteosarcoma, as opposed to HLA-II. Patients with CD99-low/HLA-II-high expression had the lowest overall and disease-free survival rates, and conjoined expression of CD99/HLA-II was an independent prognostic indicator of osteosarcoma.

CONCLUSION

These findings suggest for the first time that CD99 downregulation or HLA-II upregulation may be an important feature of human osteosarcoma. The combined detection of CD99/HLA-II coexpression may present a predictive and prognostic indicator in osteosarcoma.

CD99 drives terminal differentiation of osteosarcoma cells by acting as a spatial regulator of ERK 1/2

Differentiation therapy is an attractive treatment for osteosarcoma (OS). CD99 is a cell surface molecule expressed in mesenchymal stem cells and osteoblasts that is maintained during osteoblast differentiation while lost in OS. Herein, we show that whenever OS cells regain CD99, they become prone to reactivate the terminal differentiation program. In differentiating conditions, CD99-transfected OS cells express osteocyte markers, halt proliferation, and largely die by apoptosis, resembling the fate of mature osteoblasts. CD99 induces ERK activation, increasing its membrane-bound/cytoplasmic form rather than affecting its nuclear localization. Through cytoplasmic ERK, CD99 promotes activity of the main osteogenic transcriptional factors AP1 and RUNX2, which in turn enhance osteocalcin and p21(WAF1/CIP1) , leading to G0 /G1 arrest. These data underscore the alternative positions of active ERK into distinct subcellular compartments as key events for determining OS fate.

Hypoxia induces connexin 43 dysregulation by modulating matrix metalloproteinases via MAPK signaling

Connexin 43 (Cx43) is a major structural protein found in the gap junctions of the ventricular myocardium and a major determinant of its electrical properties. The effects of matrix metalloproteinases (MMPs), the mitogen-activated protein kinase (MAPK) signaling pathway, transcription factor NF-kB, and activator protein-1 (AP-1)/c-Jun on the regulation of Cx43 gene expression in H9c2 cardiomyocytes were assessed. The MAPK signaling pathway (MEK/ERK1/2 and PI3K) and transcription factors NF-kB and AP-1/c-Jun were inhibited, then Cx43 expression was assessed using Western blot analysis, and MMP-9 activity was assessed using gelatin zymography. Hypoxia decreased the Cx43 protein level by approximately 30-50 %. Doxycycline (10 μg/mL), an inhibitor of MMP, markedly attenuated the hypoxia-induced downregulation of Cx43 protein expression at 6 h. The hypoxia-induced decrease in Cx43 protein expression was significantly reversed by U0126 (10 μM), a MEK/ERK1/2 inhibitor, at 6 and 12 h; LY294002 (30 μM), a PI3K inhibitor, downregulated Cx43 expression. Hypoxia-induced MMP-9 activation was inhibited by treatment with LY294002, U0126, and, most especially, U0126. JSH-23 (30 μM), an NF-kB inhibitor, and SP600125 (10 μM), an AP-1/c-Jun inhibitor, attenuated the loss of Cx43. These results suggest that MAPK signaling and the activities NF-kB and MMPs play an important roles in the regulation of Cx43 expression.

Crosstalk between breast cancer stem cells and metastatic niche: emerging molecular metastasis pathway?

Metastatic colonization represents the final step of metastasis, and is the major cause of cancer mortality. Metastasis as an "inefficient" process requires the right population of tumor cells in a suitable microenvironment to form secondary tumors. Cancer stem cells are the only capable population of tumor cells to progress to overt metastasis. On the other hand, the occurrence of appropriate microenvironmental conditions within the target tissue would be critical for metastasis formation. Metastatic niche seems to be the specialized microenvironment to support tumor initiating cells at the distant organ. Master regulators not only determine cancer stem cell state, but also may have regulatory roles in metastatic niche elements. Meanwhile, both cancer stem cell and metastatic niche may function like two sides of the metastatic coin. Hypoxia inducible factors have multiple roles in regulation of both sides of this coin. TGF-β superfamily, also, have been considered as master regulators of epithelial to mesenchymal transition and metastasis and may play crucial roles in regulation of metastatic niche as well. In this regard, we hypothesize the presence of a possible emerging molecular pathway in the biological process of breast cancer metastasis. In this process, non-Smad TGF-β-induced metastasis connects cancer stem cell and metastatic niche formation through a central path, "Metastasis Pathway".

CD99 suppresses osteosarcoma cell migration through inhibition of ROCK2 activity

CD99, a transmembrane protein encoded by MIC2 gene is involved in multiple cellular events including cell adhesion and migration, apoptosis, cell differentiation and regulation of protein trafficking either in physiological or pathological conditions. In osteosarcoma, CD99 is expressed at low levels and functions as a tumour suppressor. The full-length protein (CD99wt) and the short-form harbouring a deletion in the intracytoplasmic domain (CD99sh) have been associated with distinct functional outcomes with respect to tumour malignancy. In this study, we especially evaluated modulation of cell-cell contacts, reorganisation of the actin cytoskeleton and modulation of signalling pathways by comparing osteosarcoma cells characterised by different metastasis capabilities and CD99 expression, to identify molecular mechanisms responsible for metastasis. Our data indicate that forced expression of CD99wt induces recruitment of N-cadherin and β-catenin to adherens junctions. In addition, transfection of CD99wt inhibits the expression of several molecules crucial to the remodelling of the actin cytoskeleton, such as ACTR2, ARPC1A, Rho-associated, coiled-coil containing protein kinase 2 (ROCK2) as well as ezrin, an ezrin/radixin/moesin family member that has been clearly associated with tumour progression and metastatic spread in osteosarcoma. Functional studies point to ROCK2 as a crucial intracellular mediator regulating osteosarcoma migration. By maintaining c-Src in an inactive conformation, CD99wt inhibits ROCK2 signalling and this leads to ezrin decrease at cell membrane while N-cadherin and β-catenin translocate to the plasma membrane and function as main molecular bridges for actin cytoskeleton. Taken together, we propose that the re-expression of CD99wt, which is generally present in osteoblasts but lost in osteosarcoma, through inhibition of c-Src and ROCK2 activity, manages to increase contact strength and reactivate stop-migration signals that counteract the otherwise dominant promigratory action of ezrin in osteosarcoma cells.

Overexpression of CD99 Increases the Migration and Invasiveness of Human Malignant Glioma Cells

The malignant glioma is the most common primary human brain tumor, and its migration and invasiveness away from the primary tumor mass are considered a leading cause of tumor recurrence and treatment failure. Recently, gene expression profiling revealed that the transmembrane glycoprotein CD99 is more highly expressed in malignant glioma than in normal brain. Although its function is not completely understood, CD99 is implicated in cell adhesion and migration in a variety of different cell types. CD99 has wild-type and splice variant isoforms. Previous studies have shown that wild-type CD99 may be an oncosuppressor in some tumors, distinct from the role of the splice variant isoform. In this study, our data reveal that only wild-type CD99 is expressed in human glioma cells and tissues. Using a tissue microarray, we validated that gliomas demonstrate higher expression of CD99 compared with nonneoplastic brain. To assess the role of CD99 in glioma migration and invasion, we inhibited CD99 expression by siRNA and demonstrated decreased glioma migration and invasion. In contrast, when CD99 was overexpressed in glioma cells, we observed enhancement of cell migration and invasiveness. An orthotopic brain tumor model demonstrates that CD99 overexpression significantly increases invasiveness and decreases survival rate. Interestingly, Rac activity was decreased and Rho activity was increased in CD99 overexpressing glioma cells, and the proportion of amoeboid cells to mesenchymal cells was significantly increased. Taken together, our findings suggest that CD99 may play an important role in the migration and invasion of human gliomas independent of Akt, ERK, or JNK signaling pathways. Moreover, CD99 might be involved in amoeboid-mesenchymal transition in glioma migration. CD99 may be an important future target to inhibit migration and invasion, especially in CD99-expressing gliomas.