| 1989 |
The MIC2 (CD99) gene product is an integral membrane protein with a single long hydrophobic transmembrane domain; epitope mapping with six monoclonal antibodies localized all recognized epitopes to the extracellular region, establishing the protein's orientation in the plasma membrane. |
Epitope library screening with monoclonal antibodies, hydropathy plot analysis, plasmid expression vectors |
Molecular immunology |
Medium |
2465491
|
| 1989 |
CD99 (E2/MIC2 gene product) is a 32 kDa glycoprotein expressed on T-cell surfaces that is involved in spontaneous rosette formation with erythrocytes and T-cell adhesion processes; the protein is rich in proline residues, lacks N-linked glycosylation sites, and has a structure typical of an integral membrane protein. |
cDNA cloning, nucleotide sequencing, Northern blot, monoclonal antibody characterization |
The EMBO journal |
Medium |
2479542
|
| 1984 |
MIC2X escapes X-chromosome inactivation on both structurally normal and abnormal inactive human X chromosomes. |
Cell hybrid analysis, expression assays on inactive X chromosomes |
American journal of human genetics |
High |
6540985
|
| 1988 |
The MIC2 HTF island (CpG-rich region at the 5' end) is unmethylated on both active and inactive X chromosomes and on the Y chromosome, correlating with the gene's escape from X-chromosome inactivation; this contrasts with X-inactivated genes whose HTF islands are highly methylated on the inactive X. |
HpaII restriction digestion, Southern blotting, methylation analysis |
Proceedings of the National Academy of Sciences of the United States of America |
High |
2456574
|
| 1997 |
The CD99 gene encodes two distinct proteins via alternative splicing: a major full-length form that induces LFA-1/ICAM-1-mediated homotypic adhesion of B lymphocytes, and a minor truncated form that inhibits this adhesion process and markedly down-regulates LFA-1 expression when overexpressed. |
Alternative splicing characterization, transfection of isoforms into IM-9 B cells, blocking antibodies to LFA-1 and ICAM-1, cell aggregation assays |
Journal of immunology |
High |
9278313
|
| 1998 |
Downregulation of CD99 in B-cell lines leads to generation of cells with Hodgkin and Reed-Sternberg (H-RS) phenotype (multinuclearity, CD15 expression, decreased MHC class I and CD45RB, deregulated cytokine secretion); forced re-expression of CD99 or a constitutively active form of Rac abolishes these features, placing CD99 upstream of a Rac-Rho signaling pathway. |
Antisense CD99 transfection, forced CD99 expression, constitutively active Rac transfection, immunophenotyping, cytokine measurement |
Blood |
High |
9834235
|
| 2000 |
CD99 ligation upregulates alpha4beta1 integrin-dependent T-cell firm adhesion to vascular endothelium under physiological shear stress; this activation is dependent on the alpha4beta1-VCAM-1 pathway but does not activate the alphaLbeta2-ICAM-1 pathway. |
Flow chamber adhesion assay under shear stress, blocking antibodies to integrins and adhesion molecules, T cell line and peripheral blood lymphocyte studies |
European journal of immunology |
High |
11069091
|
| 2001 |
Engagement of specific CD99 epitopes by the monoclonal antibody Ad20 rapidly induces caspase-independent programmed cell death in transformed T cell lines; this death pathway proceeds independently of CD3, CD4, CD45, and p56lck, and is not influenced by CD47 signaling. |
Morphological analysis, phosphatidylserine exposure (annexin V), propidium iodide uptake, comparison with Fas and TRAIL death pathways, signaling molecule blockade |
Journal of immunology |
Medium |
11290771
|
| 2002 |
The full-length CD99 isoform (long form) promotes CD99-induced cell adhesion in Jurkat T cells, whereas co-expression of both long and short isoforms is required to trigger T-cell death; the two isoforms form covalent heterodimers that localize within glycosphingolipid rafts and induce sphingomyelin degradation; cholesterol depletion prevents raft localization and blocks apoptosis induction. |
Transfection of individual and combined CD99 isoforms in CD99-deficient Jurkat cells, heterodimer detection, raft fractionation, cholesterol depletion, sphingomyelin degradation assay |
FASEB journal |
High |
12368226
|
| 2000 |
CD99-induced homotypic aggregation of Jurkat T cells is mediated through a beta2-integrin-independent pathway requiring protein tyrosine kinase activity, protein kinase C activity, and actin filament polymerization, as demonstrated by inhibition with genistein, sphingosine, and cytochalasin B respectively. |
Homotypic aggregation assay, pharmacological inhibitors of PKC, PTK, and actin polymerization, anti-LFA-1 and anti-ICAM-1 blocking antibodies |
Immunology letters |
Medium |
10709783
|
| 2004 |
Mouse CD99 is expressed on leukocytes and concentrated at endothelial cell contacts; CD99 mediates homophilic cell aggregation (blocked by anti-CD99 antibodies), participates in transendothelial migration of lymphocytes in vitro, and in vivo anti-CD99 antibodies inhibit T-cell recruitment to inflamed skin in a cutaneous delayed-type hypersensitivity model. |
cDNA cloning, CHO cell transfection aggregation assay, in vitro TEM assay, in vivo DTH model with antibody blockade |
Blood |
High |
15280198
|
| 2006 |
CD99 acts as a tumor suppressor in osteosarcoma: forced CD99 expression reduces anoikis resistance, anchorage-independent growth, cell migration, and abrogates tumorigenicity and metastatic ability; mechanistically, CD99 expression induces caveolin-1 upregulation, the two proteins colocalize on the cell surface, and antisense caveolin-1 abrogates CD99's effect on migration; CD99 also inhibits c-Src kinase activity. |
CD99 transfection in osteosarcoma cell lines, xenograft assays, anchorage-independent growth, migration assays, co-localization studies, antisense oligonucleotides to caveolin-1, c-Src kinase activity assay |
Molecular biology of the cell |
High |
16421247
|
| 2007 |
CD99 is a key mediator of neutrophil transendothelial migration (TEM); blocking CD99 on either neutrophils or endothelial cells with Fab fragments blocks >80% of PMN TEM in vitro, suggesting homophilic interaction; CD99-blocked neutrophils are arrested at a step distal to PECAM-blocked neutrophils within endothelial junctions, indicating CD99 and PECAM regulate distinct sequential diapedesis steps. |
In vitro TEM assay with HUVEC monolayers, Fab fragment blocking antibodies applied to neutrophils or endothelial cells separately, confocal microscopy, shear stress TEM assay |
Journal of immunology |
High |
17202377
|
| 2007 |
The two CD99 isoforms have opposite functions in tumor malignancy: the full-length form (CD99wt) inhibits anchorage-independent growth, anoikis resistance, migration, and metastasis, whereas the short form (CD99sh) promotes these phenomena; the Ser168 residue of CD99 plays a pivotal role in the reversion of malignant phenotype; mechanistically, both isoforms regulate c-Src family kinase activity in opposite directions. |
Forced overexpression of CD99wt and CD99sh in osteosarcoma and prostate cancer cells, anchorage-independent growth assays, anoikis assays, migration assays, metastasis in vivo, Ser168 mutagenesis, c-Src kinase activity measurement |
Oncogene |
High |
17471235
|
| 2008 |
CD99 is essential for leukocyte diapedesis in vivo: in the thioglycollate peritonitis model, anti-murine CD99 antibody blocked neutrophil recruitment by >40% and monocyte recruitment by >80% at 18 h; blocking occurred at the luminal surface of venules; muCD99-transfected cells aggregate homophilically but do not bind cells expressing murine or human PECAM or human CD99, indicating species-specificity of the homophilic interaction. |
Murine CD99 cloning, in vitro cell transfection aggregation assay, in vivo thioglycollate peritonitis model, antibody blockade, intravital microscopy |
Cell communication & adhesion |
High |
18923973
|
| 2008 |
CD99 physically associates with HLA class I molecules via their transmembrane domains in the trans-Golgi network (TGN) and at the cell surface; CD99 is required for IFN-gamma-induced upregulation of HLA class I surface expression; CD99 also binds p230/golgin-245 (a TGN vesicle trafficking protein) through its GRIP domain, and p230 overexpression leads to downmodulation of HLA class I surface expression. |
Co-immunoprecipitation, subcellular fractionation, IFN-gamma stimulation assays, p230/golgin-245 interaction studies, overexpression experiments |
Blood |
High |
18849489
|
| 2010 |
CD99 prevents neural differentiation of Ewing sarcoma cells and thereby contributes to oncogenesis; knockdown of CD99 reduces tumor formation and bone metastases in xenograft models, induces neurite outgrowth and beta-III tubulin expression; mechanistically, CD99 knockdown leads to increased phosphorylation of ERK1/2, suggesting CD99 modulates differentiation through the MAPK pathway. |
shRNA knockdown of CD99 in EWS cell lines, xenograft assays in immunodeficient mice, neurite outgrowth quantification, beta-III tubulin and neurofilament marker expression, ERK1/2 phosphorylation measurement |
The Journal of clinical investigation |
High |
20197622
|
| 2013 |
CD99 suppresses osteosarcoma cell migration through inhibition of ROCK2 activity: CD99wt expression recruits N-cadherin and beta-catenin to adherens junctions, inhibits ACTR2, ARPC1A, ROCK2, and ezrin expression; mechanistically, CD99wt maintains c-Src in an inactive conformation, which inhibits ROCK2 signaling, causing ezrin decrease at the cell membrane and N-cadherin/beta-catenin translocation to the plasma membrane. |
CD99wt transfection in osteosarcoma cells, actin cytoskeleton imaging, co-localization of N-cadherin and beta-catenin, ROCK2 activity assays, c-Src activity measurement, ezrin localization |
Oncogene |
High |
23644663
|
| 2013 |
Poliovirus receptor (PVR/CD155) regulates a step in TEM between PECAM and CD99; sequential antibody blocking experiments establish the order PECAM → PVR/DNAM-1 → CD99 in monocyte diapedesis; PVR resides in the lateral border recycling compartment (LBRC) similar to PECAM and CD99; endothelial PVR activation recruits the tyrosine phosphatase Shp-2 in a Src kinase-dependent manner. |
Sequential antibody blocking of TEM, confocal localization to LBRC, Shp-2 recruitment assay, Src kinase inhibition |
The American journal of pathology |
Medium |
23333754
|
| 2015 |
During leukocyte TEM, endothelial CD99 signals through a complex of its lysine-rich juxtamembrane cytoplasmic tail, A-kinase anchoring protein ezrin, and soluble adenylyl cyclase (sAC) to activate PKA; PKA then stimulates membrane trafficking from the lateral border recycling compartment (LBRC) to sites of TEM; pharmacologic or genetic inhibition of sAC or PKA arrests neutrophils and monocytes partway through endothelial junctions in vitro and in vivo without affecting leukocyte adhesion. |
Co-immunoprecipitation of CD99-ezrin-sAC complex, pharmacologic inhibition of sAC and PKA, genetic knockdown, in vitro TEM assay, in vivo assay, confocal microscopy of LBRC trafficking |
The Journal of experimental medicine |
High |
26101266
|
| 2015 |
CD99 regulates neural differentiation of Ewing sarcoma cells through a CD99 → miR-34a → Notch → NF-κB signaling axis; CD99 silencing increases miR-34a (secreted into exosomes), which represses Notch pathway, leading to NF-κB inhibition and re-establishment of the neural differentiation program; delivery of exosomes from CD99-silenced EWS cells is sufficient to induce neural differentiation in recipient EWS cells. |
CD99 siRNA silencing, miR-34a quantification, Notch pathway analysis, NF-κB activity measurement, exosome isolation and transfer experiments |
Oncogene |
High |
26616853
|
| 2016 |
Anti-CD99 monoclonal antibody triggering induces methuosis (non-apoptotic vacuolar cell death) in Ewing sarcoma cells through formation of an IGF-1R/RAS/Rac1 complex that is internalized into RAB5-positive endocytic vacuoles; IGF-1R then recycles to the cell membrane while CD99 and RAS/Rac1 are sorted into immature LAMP-1-positive vacuoles whose excessive accumulation causes cell death; this process requires IGF-1R signaling and is enhanced by IGF-1. |
Anti-CD99 mAb treatment, co-immunoprecipitation of IGF-1R/RAS/Rac1 complex, endosomal sorting assays (RAB5/LAMP-1 markers), IGF-1R pathway inhibition, IGF-1 stimulation, EWS xenograft validation |
Oncotarget |
High |
27835596
|
| 2017 |
Anti-CD99 monoclonal antibodies induce death of AML and MDS cells in a SRC-family kinase-dependent manner, in the absence of immune effector cells or complement; CD99 expression enriches for functional leukemic stem cells (LSCs) as demonstrated by limiting dilution xenotransplant studies. |
Anti-CD99 mAb treatment with/without SRC family kinase inhibitors, xenotransplant limiting dilution assays, in vitro cytotoxicity assays in absence of immune effectors |
Science translational medicine |
Medium |
28123069
|
| 2017 |
Endothelial CD99 promotes leukocyte attachment to endothelium in inflamed vessels and supports rapid chemokine-induced arrest; CD99 on endothelial cells (not on leukocytes) is responsible for both attachment support and diapedesis; endothelial CD99 binds to paired immunoglobulin-like receptors (PILRs) on neutrophils in a heterophilic interaction that increases shear resistance of neutrophil attachment to ICAM-1. |
CD99 gene inactivation (knockout), intravital video microscopy of cremaster inflammation, co-precipitation of CD99 with PILRs from adherent neutrophils, soluble CD99-biotin tag transfer to PILRs, flow assay with P-selectin/ICAM-1/CD99 coimmobilization, anti-PILR antibody blocking |
Blood |
High |
28223280
|
| 2001 |
CD99 promoter activity is positively regulated by an Sp1-binding site at position -95; EBV-encoded LMP1 represses CD99 transcription through NF-κB activation domains in LMP1's cytoplasmic carboxyl terminus, independently of the Sp1 site; NF-κB inhibition restores CD99 promoter activity suppressed by LMP1. |
Promoter deletion constructs, luciferase reporter assays, Sp1 site mutagenesis, NF-κB inhibition experiments |
Blood |
High |
11369656
|
| 2002 |
CD99 short form (splice variant) expression in breast cancer cells increases cell motility through a signaling pathway dependent on src kinase and focal adhesion kinase (FAK); kinase-negative mutant src transfectants showed 80% less motility than mock cells. |
CD99 splice variant transfection, pharmacological inhibitors (PP1 for Src, phenylarsine oxide for FAK), kinase-negative mutant src transfection |
Experimental & molecular medicine |
Medium |
12216109
|
| 2012 |
Anti-CD99 antibody ligation induces upregulation of HSP70 on the cell surface and in the cytoplasm of B- and T-leukemia cell lines and primary BCP-ALL cells; CD99-induced HSP70 upregulation on leukemia cells enables NK cell-mediated cytotoxicity. |
Anti-CD99 antibody treatment, HSP70 surface and intracellular quantification by flow cytometry, NK92 cell cytotoxicity assay |
Cell death & disease |
Medium |
23152061
|
| 2019 |
CD99 long isoform in AML cells transiently increases ERK and SRC phosphorylation followed by a dramatic decrease; overexpression of the long isoform induces increased reactive oxygen species, DNA damage, apoptosis, and decreased cell viability, and in murine leukemia models delays disease progression and reduces bone marrow engraftment. |
CD99 long isoform transfection in leukemia cell lines, ERK/SRC phosphorylation measurement, ROS assay, DNA damage markers, apoptosis assays, murine xenograft models |
Haematologica |
Medium |
31371417
|
| 2019 |
CD99 ligands are expressed on monocytes, NK cells, and dendritic cells (but not on B and T cells); interaction of CD99 with its ligand upregulates IL-6 and TNF-α (but not IFN-γ) in anti-CD3-activated T cells and in CD3-negative mononuclear cells; this cytokine upregulation requires concomitant T cell activation signal. |
Recombinant CD99 protein production, CD99 ligand expression analysis by FACS, cytokine measurement (IL-6, TNF-α, IFN-γ) by ELISA/multiplex assay |
PloS one |
Medium |
31120992
|
| 2020 |
The GDF6 prodomain is a ligand for the CD99 extracellular domain; binding of the GDF6 prodomain to CD99 recruits CSK (C-terminal Src kinase) to the YQKKK motif in the intracellular domain of CD99, thereby inhibiting Src activity; GDF6 silencing causes Src hyperactivation and p21-dependent growth arrest in Ewing sarcoma cells; two GDF6 prodomain mutants linked to Klippel-Feil syndrome are hyperactive in this CD99-Src signaling pathway. |
Co-immunoprecipitation of GDF6 prodomain with CD99, domain mapping experiments, CSK recruitment assay to CD99 YQKKK motif, Src activity measurement, GDF6 silencing with growth arrest phenotype, disease mutant functional analysis |
Cell reports |
High |
33147457
|
| 2014 |
Anti-CD99 antibody triggering in Ewing sarcoma induces cell death through Mdm2 degradation and p53 reactivation; overexpression of Mdm2 or p53 silencing decreases CD99-triggered death; the p53 pathway activation is accompanied by induction of p21, bax, and mitochondrial depolarization; normal mesenchymal stem cells (lacking EWS-FLI1) do not show p53 activation and are resistant, indicating dependence on oncogenic context. |
Anti-CD99 diabody (dAbd C7) treatment, Mdm2 overexpression rescue, p53 siRNA knockdown, nutlin-3 enhancement, p21/bax induction, mitochondrial depolarization assay, EWS xenograft experiments |
Clinical cancer research |
High |
25501132
|
| 2011 |
CD99 upregulation in Hodgkin/Reed-Sternberg cells induces PRDM1/BLIMP1 expression through a CD99 → miR-9 (decrease) → PRDM1 upregulation axis; miR-9 directly targets PRDM1 mRNA; CD99 overexpression leads to CD30 and CD15 decrease, CD38 increase, and restoration of B-cell markers (PAX5, CD79α, CD19), suggesting CD99 promotes terminal B-cell differentiation. |
CD99 overexpression in cHL cell lines, miR-9 quantification, miR-9 inhibition experiments, PRDM1 expression measurement, B-cell marker analysis by flow cytometry |
International journal of cancer |
Medium |
22020966
|
| 2019 |
CD99 silencing in Ewing sarcoma cells leads to release of exosomes with oncosuppressive functions that reduce proliferation and migration and induce a more differentiated phenotype in recipient EWS cells; the key functional driver is miR-199a-3p loaded into CD99-deprived exosomes, which acts through modulation of the AP-1 signaling pathway. |
CD99 shRNA silencing, exosome isolation and transfer experiments, recipient cell proliferation and migration assays, miRNA profiling of exosomes, AP-1 signaling pathway analysis, miR-199a-3p functional validation |
Cell death & disease |
Medium |
31209202
|
| 2019 |
Nrf2 transcriptionally activates CD99 expression (identified by dual-luciferase reporter assay and ChIP); CD99 overexpression confers cisplatin resistance in ovarian cancer cells, and CD99 knockdown sensitizes cells to cisplatin; forced CD99 re-expression can rescue Nrf2-knockdown-mediated cisplatin sensitivity. |
Dual-luciferase reporter gene assay, chromatin immunoprecipitation (ChIP), CD99 overexpression and knockdown, CCK-8 cell viability after cisplatin treatment |
Biochemical and biophysical research communications |
Medium |
31472965
|
| 2021 |
Mosaic loss of chromosome Y (LOY) in leukocytes results in reduced CD99 protein abundance on the cell surface in all six types of leukocytes studied, consistent with CD99's pseudoautosomal gene location; CD proteins encoded by autosomal genes are unaffected by LOY. |
CITE-seq (simultaneous single-cell RNA and surface protein quantification), comparison of LOY vs. non-LOY cells across six leukocyte types |
Scientific reports |
Medium |
34312421
|