Group IB secretory phospholipase A2 promotes matrix metalloproteinase-2-mediated cell migration via the phosphatidylinositol 3-kinase and Akt pathway

Secretory phospholipase A(2) (sPLA(2)), abundantly expressed in various cells including fibroblasts, is able to promote proliferation and migration. Degradation of collagenous extracellular matrix by matrix metalloproteinase (MMP) plays a role in the pathogenesis of various destructive disorders, such as rheumatoid arthritis, tumor invasion, and metastasis. Here we show that group IB PLA(2) increased pro-MMP-2 activation in NIH3T3 fibroblasts. MMP-2 activity was stimulated by group IB PLA(2) in a dose- and time-dependent manner. Consistent with MMP-2 activation, sPLA(2) decreased expression of type IV collagen. These effects are due to the reduction of tissue inhibitor of metalloproteinase-2 (TIMP-2) and the activation of the membrane type1-MMP (MT1-MMP). The decrease of TIMP-2 levels in conditioned media and the increase of MT1-MMP levels in plasma membrane were observed. In addition, treatment of cells with decanoyl Arg-Val-Lys-Arg-chloromethyl ketone, an inhibitor of pro-MT1-MMP, suppressed sPLA(2)-mediated MMP-2 activation, whereas treatment with bafilomycin A1, an inhibitor of H(+)-ATPase, sustained MMP-2 activation by sPLA(2). The involvement of phosphatidylinositol 3-kinase (PI3K) and Akt in the regulation of MMP-2 activity was further suggested by the findings that PI3K and Akt were phosphorylated by sPLA(2). Expression of p85alpha and Akt mutants, or pretreatment of cells with LY294002, a PI3K inhibitor, attenuated sPLA(2)-induced MMP-2 activation and migration. Taken together, these results suggest that sPLA(2) increases the pro-MMP-2 activation and migration of fibroblasts via the PI3K and Akt-dependent pathway. Because MMP-2 is an important factor directly involved in the control of cell migration and the turnover of extracellular matrix, our study may provide a mechanism for sPLA(2)-promoted fibroblasts migration.     

TGF-β1通过激活Smad信号途径抑制PI3K/AKT信号介导的BMSC成脂分化

转化生长因子β1 (TGF-β1) 是参与骨髓间充质干细胞（BMSCs）脂肪定向分化的重要调节因子,其具体的调节机制尚不清楚. 本研究证明,BMSCs在体外分化为脂肪细胞的过程中, TGF-β1的基因表达显著下调,重组TGF-β1能够抑制BMSCs体外脂肪细胞定向分化,其分化的标志蛋白C/EBPβ和αP2的表达水平显著降低. TGF-β1在激活Smad信号通路的同时,还抑制胰岛素(脂肪分化的主要诱导剂)对PI3K/Akt信号通路的激活.加入Smad特异性阻断剂后,C/EBPβ和αP2的诱导表达恢复正常,同时PI3K/Akt信号通路的活化亦得以恢复. 结果提示,TGF-β1可通过Smad信号通路干扰脂肪细胞分化的核心信号通路-PI3K/Akt的活化,从而实现对BMSCs脂肪分化的抑制.该研究结果为肥胖等导致的心血管疾病或Ⅱ型糖尿病等的临床治疗提供有价值的参考.     

SLFN5 suppresses cancer cell migration and invasion by inhibiting MT1-MMP expression via AKT/GSK-3β/β-catenin pathway

Human SLFN5 inhibits invasions of IFNα-sensitive renal clear-cell carcinoma and melanoma cells. However, whether this inhibition is confined to these IFNα-sensitive cancers is unclear. Here we show that SLFN5 expressions on both mRNA and protein levels are significantly higher in non/low-invasive cancer cell lines (breast cancer cell line MCF7, colorectal cancer cell line HCT116 and lung cancer cell line A549) than in highly-invasive cancer cell lines (fibrosarcoma cell line HT1080 and renal clear cell cancer cell line 786-0). SLFN5 knockdown in non/low-invasive cancer cell lines enhanced MT1-MMP expression and increased migration and invasion in vitro, and in vivo. Furthermore, SLFN5 overexpression in HT1080 and 786-0 inhibited MT1-MMP expression and repressed migration and invasion. MT1-MMP is instrumental in SLFN5-controlled inhibition of cancer cell migration and invasion, as shown by MT1-MMP-knockdown and -overexpression analyses. SLFN5 knockdown activated AKT/GSK-3β/β-catenin pathway by promotion AKT phosphorylation and subsequent GSK-3β phosphorylation, further β-catenin translocation into nucleus as un-phosphorylated protein at Ser33, 37 and 45 and Thr41 sites. This is the first study to report that SLFN5 inhibits cancer migration and invasiveness in several common cancer cell lines by repressing MT1-MMP expression via the AKT/GSK-3β/β-catenin signalling pathway, suggesting that SLFN5 plays wide inhibitory roles in various cancers.     

FAK-mediated src phosphorylation of endophilin A2 inhibits endocytosis of MT1-MMP and promotes ECM degradation

Focal adhesion kinase (FAK) is an important mediator of integrin signaling in the regulation of cell proliferation, survival, migration, and invasion. To understand how FAK contributes to cell invasion, we explored the regulation of matrix metalloproteinases (MMPs) by FAK. We found that v-Src-transformed cells activate a FAK-dependent mechanism that attenuates endocytosis of MT1-MMP. This in turn increases cell-surface expression of MT1-MMP and cellular degradation of extracellular matrix. Further, we identified an interaction between FAK's second Pro-rich motif and endophilin A2's SH3 domain. This interaction served as an autophosphorylation-dependent scaffold to allow Src phosphorylation of endophilin A2 at Tyr315. Tyr315 phosphorylation inhibited endophilin/dynamin interactions, and blockade of Tyr315 phosphorylation promoted endocytosis of MT1-MMP. Together, these results suggest a regulatory mechanism of cell invasion whereby FAK promotes cell-surface presentation of MT1-MMP by inhibiting endophilin A2-dependent endocytosis.     

Membrane Type 1–Matrix Metalloproteinase/Akt Signaling Axis Modulates TNF-α-Induced Procoagulant Activity and Apoptosis in Endothelial Cells

Membrane type 1–matrix metalloproteinase (MT1-MMP) functions as a signaling molecule in addition to a proteolytic enzyme. Our hypothesis was that MT1-MMP cooperates with protein kinase B (Akt) in tumor necrosis factor (TNF)-α-induced signaling pathways of vascular responses, including tissue factor (TF) procoagulant activity and endothelial apoptosis, in cultured human aortic endothelial cells (ECs). TNF-α (10 ng/mL) induced a decrease in Akt phosphorylation within 60 minutes in ECs. A chemical inhibitor of MMP, TIMP-2 and selective small interfering RNA (siRNA)-mediated suppression of MT1-MMP reversed TNF-α-triggered transient decrease of Akt phosphorylation within 60 minutes, suggesting that MT1-MMP may be a key regulator of Akt phosphorylation in TNF-α-stimulated ECs. In the downstream events, TNF-α increased TF antigen and activity, and suppressed the expression of thrombomodulin (TM) antigen. Inhibition of Akt markedly enhanced TNF-α-induced expression of TF antigen and activity, and further reduced the expression of TM antigen. Silencing of MT1-MMP by siRNA also reversed the changed expression of TF and TM induced by TNF-α. Moreover, TNF-α induced apoptosis of ECs through Akt- and forkhead box protein O1 (FoxO1)-dependent signaling pathway and nuclear factor-kB (NF-kB) activation. Knockdown of MT1-MMP by siRNA reversed apoptosis of ECs by inhibiting TNF-α-induced Akt-dependent regulation of FoxO1 in TNF-α-stimulated ECs. Immunoprecipitation demonstrated that TNF-α induced the changes in the associations between the cytoplasmic fraction of MT1-MMP and Akt in ECs. In conclusion, we show new evidence that MT1-MMP/Akt signaling axis is a key modifier for TNF-α-induced signaling pathways for modulation of procoagulant activity and apoptosis of ECs.     

PDGF-BB-induced MT1-MMP expression regulates proliferation and invasion of mesenchymal stem cells in 3-dimensional collagen via MEK/ERK1/2 and PI3K/AKT signaling

Mesenchymal stem cells (MSCs) mobilize membrane type-1 matrix metalloproteinase (MT1-MMP) to traffic through both 3-dimensional (3D) collagen as well as basement membrane barriers, but factors capable of regulating the expression and activity of the protease remain unidentified. Herein, we report that the MT1-MMP-dependent invasive activities of rat MSCs are controlled by PDGF-BB. Furthermore, PDGF-BB also stimulates MSC proliferation in 3D type I collagen via an MT1-MMP-dependent process that is linked to pericellular collagen degradation. PDGF-BB stimulates MT1-MMP expression at both the mRNA and protein levels in concert with ERK1/2 and PI3K/AKT activation. Inhibition of ERK1/2 or PI3K/AKT activity potently suppresses both MT1-MMP-dependent invasive and proliferative activities. Basement membrane invasion is likewise stimulated by PDGF-BB in an MT1-MMP-dependent manner via ERK1/2 and PI3K/AKT signaling. Taken together, these data serve to identify PDGF-BB as an important MSC agonist that controls invasive and proliferative activities via MT1-MMP-dependent processes that are regulated by the ERK1/2 and PI3K/AKT signaling pathways.     

Phosphorylation of membrane type 1-matrix metalloproteinase (MT1-MMP) and its vesicle-associated membrane protein 7 (VAMP7)-dependent trafficking facilitate cell invasion and migration

In multicellular organisms, uncontrolled movement of cells can contribute to pathological conditions, such as multiple sclerosis and cancer. In highly aggressive tumors, the expression of matrix metalloproteinases (MMPs) is linked to the capacity of tumor cells to invade surrounding tissue and current research indicates that the membrane-anchored membrane type 1-matrix metalloproteinase (MT1-MMP) has a central role in this process. Endocytosis and trafficking of MT1-MMP are essential for its proper function, and here we examine the phosphorylation, internalization, and recycling of this enzyme, and the associated biochemical signaling in HeLa and HT-1080 fibrosarcoma cells. Activation of protein kinase C with phorbol 12-myristate 13-acetate resulted in phosphorylation of endogenous MT1-MMP at Thr(567) in vivo. Mutation of Thr(567) to alanine (to mimic non-phosphorylated MT1-MMP) reduced internalization of MT1-MMP, whereas mutation of Thr(567) to glutamic acid (to mimic phosphorylation) resulted in decreased levels of MT1-MMP on the cell surface. The endosomal trafficking and recycling of MT1-MMP was found to be dependent upon Rab7 and VAMP7, and blocking the function of these proteins reduced cell migration and invasion. Intracellular trafficking of MT1-MMP was observed to be coupled to the trafficking of integrin α5 and phosphorylation of ERK that coincided with this was dependent on phosphorylation of MT1-MMP. Together, these results reveal important roles for MT1-MMP phosphorylation and trafficking in both cell signaling and cell invasion.     

Hepatoma-derived growth factor stimulates podosome rosettes formation in NIH/3T3 cells through the activation of phosphatidylinositol 3-kinase/Akt pathway

Hepatoma-derived growth factor (HDGF) stimulates the migration, invasion and metastasis in several types of cancer cells. However, the mechanism underlying HDGF-stimulated migration remains unclear. In this study, we investigated the influence of HDGF on cytoskeleton remodeling and phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway in non-transformed NIH/3T3 cells. Exogenous HDGF promoted the migration and the formation of dorsal ruffles and podosome rosettes. Besides, HDGF supply increased the PI3K expression and Akt phosphorylation in dose- and time-dependent manners. Application of LY294002, a PI3K inhibitor, attenuated the HDGF-induced migration, dorsal ruffles and podosome rosettes formation. Consistently, the HDGF-overexpressing NIH/3T3 transfectants exhibited significantly increased motility and elevated PI3K/Akt activities, which were repressed by LY294002 or adenovirus-mediated overexpression of endogenous PI3K antagonist, PTEN. In summary, HDGF elicits the activation of PI3K/Akt signaling cascade, thereby promoting cytoskeleton remodeling to stimulate cellular migration.     

Fibroblast Growth Factor Receptor-2 Contributes to the Basic Fibroblast Growth Factor-Induced Neuronal Differentiation in Canine Bone Marrow Stromal Cells via Phosphoinositide 3-Kinase/Akt Signaling Pathway

Bone marrow stromal cells (BMSCs) are considered as candidates for regenerative therapy and a useful model for studying neuronal differentiation. The role of basic fibroblast growth factor (bFGF) in neuronal differentiation has been previously studied; however, the signaling pathway involved in this process remains poorly understood. In this study, we investigated the signaling pathway in the bFGF-induced neuronal differentiation of canine BMSCs. bFGF induced the mRNA expression of the neuron marker, microtubule associated protein-2 (MAP2) and the neuron-like morphological change in canine BMSCs. In the presence of inhibitors of fibroblast growth factor receptors (FGFR), phosphatidylinositol 3-kinase (PI3K) and Akt, i.e., SU5402, LY294002, and MK2206, respectively, bFGF failed to induce the MAP2 mRNA expression and the neuron-like morphological change. bFGF induced Akt phosphorylation, but it was attenuated by the FGFR inhibitor SU5402 and the PI3K inhibitor LY294002. In canine BMSCs, expression of FGFR-1 and FGFR-2 was confirmed, but only FGFR-2 activation was detected by cross-linking and immunoprecipitation analysis. Small interfering RNA-mediated knockdown of FGFR-2 in canine BMSCs resulted in the attenuation of bFGF-induced Akt phosphorylation. These results suggest that the FGFR-2/PI3K/Akt signaling pathway is involved in the bFGF-induced neuronal differentiation of canine BMSCs.     

Ganglioside GM3 promotes HGF-stimulated motility of murine hepatoma cell through enhanced phosphorylation of cMet at specific tyrosine sites and PI3K/Akt-mediated migration signaling

Ganglioside GM3 plays a well-documented and important role in the regulation of tumor cell proliferation, invasion, and metastasis by modulating tyrosine kinase growth factor receptors. However, the effect of GM3 on the hepatocyte growth factor receptor (HGFR, cMet) has not been fully delineated. In the current study, we investigated how GM3 affects cMet signaling and HGF-stimulated cell motility and migration using three hepatic cancer cell lines of mouse (Hca/A2, Hca/16A3, and Hepa1-6). Decreasing GM3 expression with the use of P4, a specific inhibitor for ganglioside synthesis inhibited the HGF-stimulated phosphorylation of cMet and activity of PI3K/Akt signaling pathway. In contrast, the increased expression of GM3 as a result of adding exogenous GM3 enhanced the HGF-stimulated phosphorylation of cMet and activity of PI3K/Akt signaling pathway. Furthermore, HGF-stimulated cell motility and migration in vitro were inhibited by reduced expression of GM3 and enhanced by increased expression of GM3. All the observations indicate that ganglioside GM3 promotes HGF-stimulated motility of murine hepatoma cell through enhanced phosphorylation of cMet at specific tyrosine sites and PI3K/Akt-mediated migration signaling.     

Thrombin induces expression of FGF-2 via activation of PI3K-Akt-Fra-1 signaling axis leading to DNA synthesis and motility in vascular smooth muscle cells

To understand the mechanisms by which thrombin induces vascular smooth muscle cell (VSMC) DNA synthesis and motility, we have studied the role of phosphatidylinositol 3-kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR)-S6K1 signaling. Thrombin stimulated the phosphorylation of Akt and S6K1 in VSMC in a sustained manner. Blockade of PI3K-Akt-mTOR-S6K1 signaling by LY-294002, and rapamycin suppressed both thrombin-induced VSMC DNA synthesis and migration. Adenovirus-mediated expression of dominant-negative Akt also inhibited thrombin-induced VSMC DNA synthesis and migration. Furthermore, thrombin induced the expression of Fra-1 in a sustained PI3K-Akt-dependent and mTOR-independent manner in VSMC. Suppression of Fra-1 by its small interfering RNA attenuated both thrombin-induced VSMC DNA synthesis and migration. Thrombin also induced the expression of FGF-2 in a PI3K-Akt-Fra-1-dependent and mTOR-independent manner, and neutralizing anti-FGF-2 antibodies inhibited thrombin-stimulated VSMC DNA synthesis and motility. In addition, thrombin stimulated the tyrosine phosphorylation of EGF receptor (EGFR), and inhibition of its kinase activity significantly blocked Akt and S6K1 phosphorylation, Fra-1 and FGF-2 expression, DNA synthesis, and motility induced by thrombin in VSMC. Together these observations suggest that thrombin induces both VSMC DNA synthesis and motility via EGFR-dependent stimulation of PI3K/Akt signaling targeting in parallel the Fra-1-mediated FGF-2 expression and mTOR-S6K1 activation.     

JNK and PI3K differentially regulate MMP-2 and MT1-MMP mRNA and protein in response to actin cytoskeleton reorganization in endothelial cells

Increased production and activation of matrix metalloproteinase-2 (MMP-2) are critical events in skeletal muscle angiogenesis and are known to occur in response to mechanical stresses. We hypothesized that reorganization of the actin cytoskeleton would increase endothelial cell production and activation of MMP-2 and that this increase would require a MAPK-dependent signaling pathway in endothelial cells. The pharmacological actin depolymerization agent cytochalasin D increased expression of MMP-2 and membrane type 1-matrix metalloproteinase (MT1-MMP) mRNA, and this was reduced significantly in the presence of the JNK inhibitor SP600125. Activation of JNK by anisomycin was sufficient to induce expression of both MMP-2 and MT1-MMP mRNA in quiescent cells. Downregulation of c-Jun, a downstream target of JNK, with small interference (si)RNA inhibited MMP-2 expression in response to anisomycin. Inhibition of phosphoinositide 3-kinase (PI3K), but not JNK, significantly decreased the amount of active MMP-2 following cytochalasin D stimulation with a concurrent decrease in MT1-MMP protein. Physiological reorganization of actin occurs during VEGF stimulation. VEGF-induced MMP-2 protein production and activation, as well as MT1-MMP protein production, depended on PI3K activity. VEGF-induced MMP-2 mRNA expression was reduced by inhibition of JNK or by treatment with c-Jun siRNA. In summary, our results provide novel insight into the signaling cascades initiated in the early stages of angiogenesis through the reorganization of the actin cytoskeleton and demonstrate a critical role for JNK in regulating MMP-2 and MT1-MMP mRNA expression, whereas PI3K regulates protein levels of both MMP-2 and MT1-MMP. angiogenesis; mechanotransduction; vascular endothelial growth factor; c-Jun; phosphoinositide 3-kinase; membrane type 1-matrix metalloproteinase     

MT1-MMP down-regulates the glucose 6-phosphate transporter expression in marrow stromal cells: a molecular link between pro-MMP-2 activation, chemotaxis, and cell survival

Bone marrow-derived stromal cells (BMSC) are avidly recruited by experimental vascularizing tumors, which implies that they must respond to tumor-derived growth factor cues. In fact, BMSC chemotaxis and cell survival are regulated, in part, by the membrane type-1 matrix metalloproteinase (MT1-MMP), an MMP also involved in pro-MMP-2 activation and in degradation of the extracellular matrix (ECM). Given that impaired chemotaxis was recently observed in bone marrow cells isolated from a glucose 6-phosphate transporter-deficient (G6PT-/-) mouse model, we sought to investigate the potential MT1-MMP/G6PT signaling axis in BMSC. We show that MT1-MMP-mediated activation of pro-MMP-2 by concanavalin A (ConA) correlated with an increase in the sub-G1 cell cycle phase as well as with cell necrosis, indicative of a decrease in BMSC survival. BMSC isolated from Egr-1-/- mouse or MT1-MMP gene silencing in BMSC with small interfering RNA (siMT1-MMP) antagonized both the ConA-mediated activation of pro-MMP-2 and the induction of cell necrosis. Overexpression of recombinant full-length MT1-MMP triggered necrosis and this was signaled through the cytoplasmic domain of MT1-MMP. ConA inhibited both the gene and protein expression of G6PT, while overexpression of recombinant G6PT inhibited MT1-MMP-mediated pro-MMP-2 activation but could not rescue BMSC from ConA-induced cell necrosis. Cell chemotaxis in response to the tumorigenic growth factor sphingosine 1-phosphate was significantly abrogated in siMT1-MMP BMSC and in chlorogenic acid-treated BMSC. Altogether, we provide evidence for an MT1-MMP/G6PT signaling axis that regulates BMSC survival, ECM degradation, and mobilization. This may lead to optimized clinical applications that use BMSC as a platform for the systemic delivery of therapeutic or anti-cancer recombinant proteins in vivo.     

Curcumin inhibits the invasion of thyroid cancer cells via down-regulation of PI3K/Akt signaling pathway

The objectives of this study were to evaluate the in vitro anti-tumor (human thyroid cancer cell lines) potential of curcumin and to elucidate its molecular mechanisms. Here, we investigated the effects of curcumin on the cell viability, apoptosis, migration and invasion of human thyroid cancer cell lines FTC133. We also investigated the effects of curcumin on PI3K, p-Akt, MMP1/7, and COX-2 protein expressions using Western blot. Results showed that curcumin inhibited growth, cell migration and invasion in FTC133, and promoted its apoptosis. Western blot assay data demonstrated that curcumin inhibited phosphorylation of PI3K and Akt signaling pathways and subsequently attenuated MMP1/7 and COX-2 protein expressions in FTC133. In conclusion, curcumin suppresses FTC133 cell invasion and migration by inhibiting PI3K and Akt signaling pathways. Therefore, curcumin produces anti-metastatic activity in FTC133 cells.     

A truncated kringle domain of human apolipoprotein(a) inhibits the activation of extracellular signal-regulated kinase 1 and 2 through a tyrosine phosphatase-dependent pathway

Most proangiogenic factors exert their biological effects primarily by activating extracellular signal-regulated kinase (ERK) and phosphoinositide 3-kinase (PI3-K)/Akt signaling pathways. These pathways appear to play a critical role in endothelial cell migration, because selective inhibition of either ERK or PI3-K/Akt signaling almost completely prevented endothelial cell migration. Recently, we demonstrated that a truncated kringle domain of human apolipoprotein(a), termed rhLK68, inhibits endothelial cell migration in vitro. However, its mechanism of action was not well defined. In this study, we determined the effects of rhLK68 on ERK1/2 and PI3-K/Akt signaling pathways to explore the molecular mechanism of rhLK68-mediated inhibition of endothelial cell migration. Treatment with rhLK68 inhibited ERK1/2 phosphorylation but did not influence Akt activation. Interestingly, an inhibitor of protein-tyrosine phosphatase, sodium orthovanadate, dose-dependently reversed both rhLK68-induced dephosphorylation of ERK1/2 and decreased migration of endothelial cells, whereas rhLK68 showed no significant effects on MEKs phosphorylation. In conclusion, these results indicate that inhibition of endothelial cell migration by rhLK68 may be achieved by interfering with ERK1/2 activation via a protein-tyrosine phosphatase-dependent pathway.     

Knockdown of sphingosine kinase 1 inhibits the migration and invasion of human rheumatoid arthritis fibroblast-like synoviocytes by down-regulating the PI3K/AKT activation and MMP-2/9 production in vitro

To investigate the potential regulation of sphingosine kinase 1 (SPHK1) on the migration, invasion, and matrix metalloproteinase (MMP) expression in human rheumatoid arthritis fibroblast-like synoviocytes (RA-FLS). RA-FLS were transfected control siRNA or SPHK1 siRNA. The migration and invasion of unmanipulated control, control siRNA or SPHK1 siRNA- transfected RA-FLS in vitro were measured by the transwell system. The relative levels of SPHK1, PI3K, and AKT as well as AKT phosphorylation in RA-FLS were determined by Western blot. The levels of MMP-2/9 secreted by RA-FLS were detected by ELISA. Knockdown of SPHK1 significantly inhibited the spontaneous migration and invasion of RA-FLS, accompanied by significantly reduced levels of PI3K expression and AKT phosphorylation. Similarly, treatment with LY294002, an inhibitor of the PI3K/AKT pathway, inhibited the migration and invasion of RA-FLS. Knockdown of SPHK1 and treatment with the inhibitor synergistically inhibited the migration and invasion of RA-FLS, by further reducing the levels of PI3K expression and AKT phosphorylation. In addition, knockdown of SPHK1 or treatment with LY294002 inhibited the secretion of MMP-2 and MMP-9, and both synergistically reduced the production of MMP-2 and MMP-9 in RA-FLS in vitro. Knockdown of SPHK1 expression inhibits the PI3K/AKT activation, MMP-2 and MMP-9 expression, and human RA-FLS migration and invasion in vitro. Potentially, SPHK1 may be a novel therapeutic target for RA.     

Membrane type 1-matrix metalloproteinase is regulated by chemokines monocyte-chemoattractant protein-1/ccl2 and interleukin-8/CXCL8 in endothelial cells during angiogenesis

We have investigated the putative role and regulation of membrane type 1-matrix metalloproteinase (MT1-MMP) in angiogenesis induced by inflammatory factors of the chemokine family. The absence of MT1-MMP from null mice or derived mouse lung endothelial cells or the blockade of its activity with inhibitory antibodies resulted in the specific decrease of in vivo and in vitro angiogenesis induced by CCL2 but not CXCL12. Similarly, CCL2- and CXCL8-induced tube formation by human endothelial cells (ECs) was highly dependent on MT1-MMP activity. CCL2 and CXCL8 significantly increased MT1-MMP surface expression, clustering, activity, and function in human ECs. Investigation of the signaling pathways involved in chemokine-induced MT1-MMP activity in ECs revealed that CCL2 and CXCL8 induced cortical actin polymerization and sustained activation of phosphatidylinositol 3-kinase (PI3K) and the small GTPase Rac. Inhibition of PI3K or actin polymerization impaired CCL2-induced MT1-MMP activity. Finally, dimerization of MT1-MMP was found to be enhanced by CCL2 in ECs in a PI3K- and actin polymerization-dependent manner. In summary, we identify MT1-MMP as a molecular target preferentially involved in angiogenesis mediated by CCL2 and CXCL8, but not CXCL12, and suggest that MT1-MMP dimerization might be an important mechanism of its regulation during angiogenesis.