CD99 inhibits CD98-mediated ß1 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 ß1 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 ß1 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-ß1 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 ß1 integrin signaling by CD99 and CD98 and may provide a novel therapeutic approach to treat inflammation and cancer.

Therapeutic Effect of Anti-Inflammatory Tripeptide Cream in Hand-Foot Syndrome/Skin Reaction Related to Anticancer Drugs: a Randomized, Double-Blind, Placebo-Controlled Pilot Trial.

Purpose: Hand-foot syndrome (HFS) and hand-foot skin reaction (HFSR) are relatively common toxicities that interfere with the quality of life (QoL) of patients with cancer. Anti-inflammatory tripeptide cream (ATPC) is a complex formulation of anti-inflammatory tripeptides, the CD99-agonist BinterinTM and the Wnt-antagonist WinhibinTM. The present study aimed to assess the therapeutic effects of ATPC in HFS/HFSR associated with anticancer drugs. Materials and Methods: This was a single-center, randomized, double-blind, placebo-controlled trial. Patients who developed grade 1 HFS/HFSR after systemic anticancer treatments were enrolled, and randomly assigned to receive either ATPC or placebo cream (PC) and followed up at 3-week intervals for up to nine weeks. Primary endpoint was the development of grade ≥ 2 HFS/HFSR. Results: Between April 2019 and July 2022, 60 patients (31 in the ATPC and 29 in the PC group) completed the study. The incidence of grade ≥ 2 HFS/HFSR was significantly lower in the ATPC than in the PC group (25.8% vs. 51.7%, p=0.039). The ATPC showed trends towards a better QoL score, assessed by a HFSR and QoL questionnaire at 9 weeks (26.0 vs. 29.9, p=0.574), and a lower frequency of discontinuation, interruption, or dose reduction of anticancer drugs (51.6% vs. 58.6%, p=0.586) than the PC group over 9 weeks, though without statistical significance. Conclusion: Our results showed that ATPC significantly decreased the development of grade ≥ 2 HFS/HFSR in patients already with HFS/HFSR. Therefore, ATPC may be an effective treatment for HFS/HFSR associated with anticancer drugs.

Cancer/testis antigen CAGE exerts negative regulation on p53 expression through HDAC2 and confers resistance to anti-cancer drugs.

The role of the cancer/testis antigen CAGE in drug resistance was investigated. The drug-resistant human melanoma Malme3M (Malme3M(R)) and the human hepatic cancer cell line SNU387 (SNU387(R)) showed in vivo drug resistance and CAGE induction. Induction of CAGE resulted from decreased expression and thereby displacement of DNA methyltransferase 1(DNMT1) from CAGE promoter sequences. Various drugs induce expression of CAGE by decreasing expression of DNMT1, and hypomethylation of CAGE was correlated with the increased expression of CAGE. Down-regulation of CAGE in these cell lines decreased invasion and enhanced drug sensitivity resulting from increased apoptosis. Down-regulation of CAGE also led to decreased anchorage-independent growth. Down-regulation of CAGE led to increased expression of p53, suggesting that CAGE may act as a negative regulator of p53. Down-regulation of p53 enhanced resistance to drugs and prevented drugs from exerting apoptotic effects. In SNU387(R) cells, CAGE induced the interaction between histone deacetylase 2 (HDAC2) and Snail, which exerted a negative effect on p53 expression. Chromatin immunoprecipitation assay showed that CAGE, through interaction with HDAC2, exerted a negative effect on p53 expression in Malme3M(R) cells. These results suggest that CAGE confers drug resistance by regulating expression of p53 through HDAC2. Taken together, these results show the potential value of CAGE as a target for the development of cancer therapeutics.

A Basic Domain-Derived Tripeptide Inhibits MITF Activity by Reducing its Binding to the Promoter of Target Genes.

The keratinocytes in UV-irradiated skin produce and secrete α-melanocyte-stimulating hormone. α-Melanocyte-stimulating hormone upregulates the expression of MITF in melanocytes through the cAMP‒protein kinase A‒CREB signaling pathway. Thereafter, MITF induces the expression of melanogenic genes, including the tyrosinase gene TYR and TYRP-1 and TYRP-2 genes, which leads to the synthesis and accumulation of melanin. In this study, we examined whether MITF basic region-derived tripeptides can bind to the DNA-binding domain of MITF and inhibit MITF-induced melanogenesis through the inhibition of MITF‒DNA binding. MITF-KGR, a representative MITF-derived tripeptide, suppressed the transcriptional activity of MITF by disrupting its binding to the promoter region of the target genes, which resulted in the inhibition of skin epidermis thickness and melanin synthesis in vivo and in vitro. Our results indicate that MITF-KGR exerts an inhibitory effect on melanogenesis by targeting MITF.

Xclaudin 1 is required for the proper gastrulation in Xenopus laevis.

Claudin 1 is one of the tight junctional proteins involved in the tight sealing of the cellular sheets and plays a crucial role in the maintenance of cell polarity. Although its structure and physiological function in intercellular adhesion is relatively well understood, we have little information about its possible involvement in early development of vertebrates. We found Xclaudin 1 is expressed maternally in the oocyte of Xenopus laevis and the zygotic expression initiates stage 9 in the animal hemisphere but not in the vegetal hemisphere, limited on the ectoderm and mesoderm until the end of gastrulation. We have investigated a potential role for claudin 1 at gastrulation by gain and loss-of-function studies. Over-expression of Xclaudin 1 resulted in gastrulation defect in a dose-dependent manner. Knockdown of Xclaudin 1 by antisense morpholino oligonucleotides (MOs) blocked convergent extension, whereas ectopic expression of Xclaudin 1-myc mRNA rescued these defects. However, altered expression of Xclaudin 1 did not inhibit mesodermal gene expression. Taken together, our results suggest that Xclaudin 1 is required for proper convergent extension movement during Xenopus gastrulation.

CD99-PTPN12 Axis Suppresses Actin Cytoskeleton-Mediated Dimerization of Epidermal Growth Factor Receptor.

The epidermal growth factor receptor (EGFR), a member of ErbB receptor tyrosine kinase (RTK) family, is activated through growth factor-induced reorganization of the actin cytoskeleton and subsequent dimerization. We herein explored the molecular mechanism underlying the suppression of ligand-induced EGFR dimerization by CD99 agonists and its relevance to tumor growth in vivo. Epidermal growth factor (EGF) activated the formation of c-Src/focal adhesion kinase (FAK)-mediated intracellular complex and subsequently induced RhoA-and Rac1-mediated actin remodeling, resulting in EGFR dimerization and endocytosis. In contrast, CD99 agonist facilitated FAK dephosphorylation through the HRAS/ERK/PTPN12 signaling pathway, leading to inhibition of actin cytoskeletal reorganization via inactivation of the RhoA and Rac1 signaling pathways. Moreover, CD99 agonist significantly suppressed tumor growth in a BALB/c mouse model injected with MDA-MB-231 human breast cancer cells. Taken together, these results indicate that CD99-derived agonist ligand inhibits epidermal growth factor (EGF)-induced EGFR dimerization through impairment of cytoskeletal reorganization by PTPN12-dependent c-Src/FAK inactivation, thereby suppressing breast cancer growth.

Hyaluronic acid targets CD44 and inhibits FcepsilonRI signaling involving PKCdelta, Rac1, ROS, and MAPK to exert anti-allergic effect.

Effects of hyaluronic acid (HA) on allergic inflammation were investigated. HA exerted negative effects on beta-hexoaminidase secretion and histamine release in antigen-stimulated rat basophilic leukemia (RBL2H3) cells. HA inhibited interaction between IgE and FcepsilonRI and between FcepsilonRI and PKCdelta. HA inhibited CD44 interaction with PKCalpha, indicating that HA targets CD44. PKCalpha and -delta were responsible for increased Rac1 activity and expression of p47(phox), p67(phox). HA inhibited phosphorylation of PKCalpha and -delta. Rac1 was responsible for increased ROS, and NADPH oxidase was the main source for ROS. The inhibition of PKC prevented antigen from increasing phosphorylation of ERK and p38 MAPK. ERK, p38 MAPK, and ROS, were responsible for secretion of beta-hexosaminidase, histamine release, and induction of chemokines. HA suppressed induction of chemokines, such as MIP-2 and Sprr-2a. CD44 mediated effect of antigen on phosphorylation of ERK, p38MAPK, ROS production, secretion of beta-hexosaminidase, and histamine release. GPCR did not mediate allergic function of antigen or affect anti-allergic function of HA. In vivo anti-allergic effect of HA was investigated using Nc/Nga mice model of DNFB-induced atopic dermatitis. HA reduced skin lesions in Nc/Nga mice treated with DNFB, decreased expression levels of MIP-2, Sprr-2a, and serum IgE level. In conclusion, hyaluronic acid exerts negative effect on allergic inflammation by targeting CD44 and inhibiting FcepsilonRI signaling.

Alleviation of Ultraviolet-B Radiation-Induced Photoaging by a TNFR Antagonistic Peptide, TNFR2-SKE.

Ultraviolet (UV) radiation of the sunlight, especially UVA and UVB, is the primary environmental cause of skin damage, including topical inflammation, premature skin aging, and skin cancer. Previous reports show that activation of nuclear factor-κB (NF-κB) in human skin fibroblasts and keratinocytes after UV exposure induces the expression and release of proinflammatory cytokines, such as interleukin-1 (IL-1) and tumor necrosis factor-α (TNF-α), and subsequently leads to the production of matrix metalloproteases (MMPs) and growth factor basic fibroblast growth factor (bFGF). Here, we demonstrated that TNFR2-SKEE and TNFR2-SKE, oligopeptides from TNF receptor-associated factor 2 (TRAF2)-binding site of TNF receptor 2 (TNFR2), strongly inhibited the interaction of TNFR1 as well as TNFR2 with TRAF2. In particular, TNFR2-SKE suppressed UVB- or TNF-α-induced nuclear translocalization of activated NF-κB in mouse fibroblasts. It decreased the expression of bFGF, MMPs, and COX2, which were upregulated by TNF-α, and increased procollagen production, which was reduced by TNF-α. Furthermore, TNFR2-SKE inhibited the UVB-induced proliferation of keratinocytes and melanocytes in the mouse skin and the infiltration of immune cells into inflamed tissues. These results suggest that TNFR2-SKE may possess the clinical potency to alleviate UV-induced photoaging in human skin.

Tissue transglutaminase-induced down-regulation of matrix metalloproteinase-9.

Tissue transglutaminase (TGase 2) has been reported to have multiple functions in addition to its function as a biological adhesive. To identify its roles, we investigated the effects of TGase 2 on gelatinase activity. The MMP-9 activity of certain cell lines was significantly inhibited with retinoic acid treatment, and this effect was reversed in the presence of a TGase 2 inhibitor. Furthermore, TGase 2 overexpression reduced the MMP-9 protein expression levels and inhibited its activity in both culture media and cell lysate. The decreased mRNA levels of MMP-9 and the results of a promoter assay revealed that TGase 2 may be involved in MMP-9 transcription. Further, data obtained in an immunoprecipitation assay and an electrophoretic mobility shift assay demonstrated that TGase 2 binds to c-Jun and suppresses its binding activity toward AP-1. These results suggest that TGase 2 inhibits MMP-9 via downregulation of MMP-9 transcription activity by blocking the binding of the Jun-fos complex to an AP-1 site.

CD98 activation increases surface expression and clusteringof beta1 integrins in MCF-7 cells through FAK/Src- and cytoskeleton-independent mechanisms.

CD98, a disulfide-linked 125-kDa heterodimeric type II transmembrane glycoprotein, regulates beta1 integrin- mediated cell adhesion. However, the molecular mechanisms underlying CD98-mediated activation of beta1 integrin are presently unclear. In this study, the effects of CD98 signaling on the expression and clustering of beta1 integrin were investigated. Activation of CD98 augmented surface expression of beta1 integrin on MCF-7 cells. Cross-linking CD98 induced clustering of beta1 integrins. Inhibition of phosphorylation of focal adhesion kimase (FAK) by PP2, an inhibitor of Src family kinase, reduced cell-extracellular matrix adhesion, but not surface expression and clustering of beta1 integrin on MCF-7 cells. This result was confirmed by over-expression of dominant negative forms of FAK. In addition, phalloidin or cytochalasin D inhibited CD98-mediated induction of cell-ECM adhesion, but not surface expression and clustering of beta1 integrins. The inhibitory effects of PP2, cytochalasin D or phalloidin on CD98-stimulated cell adhesion were diminished by pretreatment of cells with Mn2+, which is shown to induce conformational change of integrins. These results provide the first evidence that CD98 activation increases not only beta1 integrin affinity but also its surface expression and clustering and the latter is independent of FAK/Src and cytoskeleton.

CD36 signaling inhibits the translation of heat shock protein 70 induced by oxidized low density lipoprotein through activation of peroxisome proliferators-activated receptor gamma.

Oxidized LDL (OxLDL), a causal factor in atherosclerosis, induces the expression of heat shock proteins (Hsp) in a variety of cells. In this study, we investigated the role of CD36, an OxLDL receptor, and peroxisome proliferator-activated receptor gamma (PPARgamma) in OxLDL-induced Hsp70 expression. Overexpression of dominant-negative forms of CD36 or knockdown of CD36 by siRNA transfection increased OxLDL-induced Hsp70 protein expression in human monocytic U937 cells, suggesting that CD36 signaling inhibits Hsp70 expression. Similar results were obtained by the inhibition of PPARgamma activity or knockdown of PPARgamma expression. In contrast, overexpression of CD36, which is induced by treatment of MCF-7 cells with troglitazone, decreased Hsp70 protein expression induced by OxLDL. Interestingly, activation of PPARgamma through a synthetic ligand, ciglitazone or troglitazone, decreased the expression levels of Hsp70 protein in OxLDL-treated U937 cells. However, major changes in Hsp70 mRNA levels were not observed. Cycloheximide studies demonstrate that troglitazone attenuates Hsp70 translation but not Hsp70 protein stability. PPARgamma siRNA transfection reversed the inhibitory effects of troglitazone on Hsp70 translation. These results suggest that CD36 signaling may inhibit stress- induced gene expression by suppressing translation via activation of PPARgamma in monocytes. These findings reveal a new molecular basis for the anti-inflammatory effects of PPARgamma.

Increased tissue transglutaminase expression in human atherosclerotic coronary arteries.

BACKGROUND AND OBJECTIVE: Transglutaminase 2 (TGase 2) is a calcium-dependent cross-linking enzyme that catalyzes a covalent iso-peptide bond between two proteins. Interestingly, this catalysis can activate the nuclear factor-kappaB (NF-kappaB) through the polymerization of the inhibitory protein of NF-kappaB (I-kappaB). The objective of the present study was to investigate the expression of TGase 2 in the human atherosclerotic human coronary artery, and the possible roles of TGase 2 in NF-kappaB activation. METHODS AND RESULTS: We explored whether expressions of TGase 2 and NF-kappaB are associated in atherosclerosis. Using human samples, we found that TGase 2 was markedly higher than normal in the neointimal tissue of atherosclerotic coronary arteries with atherosclerosis progression. TGase 2 activity was also increased approximately two-fold in the atherosclerotic vascular wall. In immunofluorescence analysis, NF-kappaB, COX-2, and TNF-alpha were co-localized at TGase 2-positive neointimal smooth muscle cells. A promoter assay test showed that NF-kappaB activity increased in both the human monocyte and human breast carcinoma cell by TGase 2, and that TGase 2-mediated NF-kappaB activation was reversed by TGase 2 siRNA. CONCLUSION: According to these results, we suggest that TGase 2 may function as an activator in the NF-kappaB pathway; this effect may occur in the atherosclerotic vessel wall.

The anti-inflammatory activity of Phellinus linteus (Berk. & M.A. Curt.) is mediated through the PKCdelta/Nrf2/ARE signaling to up-regulation of heme oxygenase-1.

It has been reported that heme oxygenase-1 (HO-1) mediates the anti-inflammatory activity of the n-BuOH subfraction (PL) prepared from fruiting bodies of Phellinus linteus. This continuing work aimed to elucidate the signaling pathway to the up-regulation of HO-1 by PL. In RAW264.7 macrophage cells, PL was able to enhance phosphorylation of protein kinase Cdelta (PKCdelta), but not PKCalpha/betaII, in a time-dependent manner. PL-induced HO-1 expression was dramatically released by GF109203X, a general inhibitor of PKC, and rottlerin, a specific PKCdelta inhibitor but not by Gö6976, a selective inhibitor for PKCalpha/beta. Additionally, PL treatment resulted in a marked increase in antioxidant response element (ARE)-driven transcriptional activity, which was dependent on PKCdelta but not PKCalpha. An increase by PL treatment in the ARE-driven transcriptional activity was further enhanced by Nrf2, whereas it was diminished by Keap1. Furthermore, pretreatment of rottlerin and overexpression of PKCdelta (K376R), a kinase-inactive form of PKCdelta, partly blocked the suppression by PL of nitric oxide (NO) production and inducible nitric oxide synthase (iNOS) expression, and iNOS promoter activity, which were elevated in the lypopolysaccharide (LPS)-activated macrophages. Similarly, expression of matrix metalloproteinase-9 (MMP-9) and its promoter activity were suppressed by PL, which were dependent upon PKCdelta. The present findings indicate that Phellinus linteus gives rise to an anti-inflammatory activity though the PKCdelta/Nrf2/ARE signaling to the up-regulation of HO-1 in an in vitro inflammation model.

CD99-Derived Agonist Ligands Inhibit Fibronectin-Induced Activation of ß1 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 ß1 integrin activity through dephosphorylation of focal adhesion kinase (FAK) at Y397. We explored a molecular mechanism underlying the suppression of ß1 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 ß1 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 ß1 integrin activation through the SHP2/ERK/PTPN12/FAK signaling pathway.

Release of heat shock protein 70 (Hsp70) and the effects of extracellular Hsp70 on matric metalloproteinase-9 expression in human monocytic U937 cells.

Heat shock protein 70 (Hsp70) release and its effects on pro-inflammatory cytokine production have been controversial. In this study, we investigated whether Hsp70 could be released from monocytes and activates matrix metalloproteinase-9 (MMP-9) gene expression. Hsp70 overexpression in human monocytic cell line U937 was found to increase PMA-induced MMP-9 expression and enhance cell motility. Hsp70 cDNA transfectants released Hsp70 protein into culture supernatants, and a part of released Hsp70 subsequently was bound to the surface of U937 cells. Addition of culture medium containing the extracelluar Hsp70 led to an increase not only in proMMP-9 secretion, but also the invasiveness of U937 cells through Matrigel or human umbilical vascular endothelial cells (HUVEC) in vitro. Immunodepletion of Hsp70 abolished its effect on MMP-9 expression. The released Hsp70 activated nuclear factor kappa B (NF-kappaB) and activating protein-1 (AP-1), which led to the activation of MMP-9 transcription. Taken together, these results suggest that extracellular Hsp70 induces the expression of MMP-9 gene through activation of NF-KappaB and AP-1.

Paired Ig-Like Type 2 Receptor-Derived Agonist Ligands Ameliorate Inflammatory Reactions by Downregulating ß1 Integrin Activity.

The paired immunoglobulin-like type 2 receptor (PILR) family consists of two functionally opposite members, inhibitory PILRα and activating PILRß receptors. PILRs are widely expressed in various immune cells and interact with their ligands, especially CD99 expressed on activated T cells, to participate in immune responses. Here we investigated whether PILR-derived agonists inhibit ß1 integrin activity as ligands for CD99. PILR-derived peptides as well as PILR-Fc fusion proteins prevented cell adhesion to fibronectin through the regulation of ß1 integrin activity. Especially, PILRpep3, a representative 3-mer peptide covering the conserved motifs of the PILR extracellular domain, prevented the clustering and activation of ß1 integrin by dephosphorylating FAK and vinculin, which are major components of focal adhesion. In addition, PILRpep3 inhibited transendothelial migration of monocytes as well as endothelial cell tube formation. Furthermore, upon intraperitoneal injection of PILRpep3 into mice with collagen-induced arthritis, the inflammatory response of rheumatoid arthritis was strongly suppressed. Taken together, these results suggest that PILR-derived agonist ligands may prevent the inflammatory reactions of rheumatoid arthritis by activating CD99.

Metastasis-suppressor KAI1/CD82 induces homotypic aggregation of human prostate cancer cells through Src-dependent pathway.

To investigate the functional role of KAI1/CD82, a metastasis suppressor for human prostate cancer, in the regulation of homotypic cell adhesion, we transfected KAI1 cDNA into DU 145 human prostate cancer cells and established stable transfectant clones with high KAI1/CD82 expression. The KAI1 transfectant cells exhibited significantly increased homotypic cell aggregation in comparison with the control transfectant cells. This aggregation of the KAI1 transfectants was further enhanced upon exposure to anti-CD82 antibody, suggesting that KAI1/CD82 may be involved in the intracellular signaling for the cell adhesion. Among several signal pathway inhibitors tested, PP1, an inhibitor of Src family kinases, significantly suppressed homotypic aggregation of the KAI1 transfectant cells. Ligation of KAI1/CD82 with anti-CD82 antibody increased endogenous Src kinase activity of the KAI1 transfectant cells. When different types of src expression constructs were retransfected into the KAI1-transfected DU 145 cells, kinase-negative mutant src transfectant cells exhibited much lower homotypic aggregation than the mock cells transfected with an empty vector. Moreover, homotypic aggregation of the mutant src transfectant cells was not enhanced by KAI1/CD82 ligation with anti- CD82 antibody. These results suggest that Src mediates the intracellular signaling pathway of KAI1/CD82 for the induction of homotypic adhesion of human prostate cancer cells.

Ox-LDL suppresses PMA-induced MMP-9 expression and activity through CD36-mediated activation of PPAR-g.

During chronic inflammatory response, mono- cytes/macrophages produce 92-kDa matrix metalloproteinase-9 (MMP-9), which may contribute to their extravasation, migration and tissue remodeling. Activation of peroxisome proliferator- activated factor receptor-g (PPAR-g) has been shown to inhibit MMP-9 activity. To evaluate whether ox-LDL, a PPAR-g activator, inhibits PMA-induced MMP-9 expression and activity, and if so, whether CD36 and PPAR-g are involved in this process, we investigated the effect of ox-LDL on MMP-9 expression and activity in PMA-activated human monocytic cell line U937. PMA-induced MMP-9 expression and activity were suppressed by the treatment with ox-LDL (50 mg/ml) or PPAR-g activators such as troglitazone (5 mM), ciglitazone (5 mM), and 15d- PGJ2 (1 mM) for 24 h. This ox-LDL or PPAR-g activator-mediated inhibition of MMP-9 activity was diminished by the pre-treatment of cells with a blocking antibody to CD36, or PGF2a (0.3 mM), which is a PPAR-g inhibitor, as well as overexpression of a dominant-negative form of CD36. Taken together, these results suggest that ox-LDL suppresses PMA-induced MMP-9 expression and activity through CD36-mediated activation of PPAR-g.

Functional involvement of src and focal adhesion kinase in a CD99 splice variant-induced motility of human breast cancer cells.

Earlier report showed that expression of a splice variant of CD99 transmembrane protein increases invasive ability of human breast cancer cells. Cell motility was also significantly enhanced by the CD99 splice variant expression. In an effort to identify the cellular components that mediate a signal transduction pathway triggered by the CD99 splice variant, known signal path inhibitors were examined for their effects on the motility of the CD99 splice variant-transfected MDA-MB-231 breast cancer cells. Phenylarsine oxide, an inhibitor of phosphatase specific for focal adhesion kinase, and PP1, an inhibitor of src kinase family, significantly suppressed motility of the cells. Among different types of src transfectant clones generated, kinase-negative mutant src transfectant cells were 80% less motile than the mock cells transfected with an empty-vector, while v-src and c-src transfectants exhibited cell motility levels at or slightly above the mock transfectant. These results suggest that src and focal adhesion kinase mediate the intracellular signaling pathway of a CD99 splice variant for the induction of motility of human breast cancer cells.