卵巢肿瘤干细胞中趋化因子表达与细胞侵袭后的转移能力

背景：利用趋化因子或趋化性多肽招募免疫效应细胞汇集于肿瘤,激发抗肿瘤免疫的方法有望成为肿瘤治疗的新策略。目的：探讨卵巢肿瘤细胞中趋化因子的表达与细胞侵袭转移能力关系。方法：采用RT-PCR方法检测卵巢肿瘤细胞系SW626和Anglne细胞株中CXCR4的表达,然后在Transwell小室检测CXCL12与CXCL12/CXCR4对SW626细胞趋化活性和侵袭活性的影响。结果与结论：RT-PCR检测结果提示SW626卵巢细胞株中有CXCR4分子的表达,而在Anglne细胞中CXCR4无表达。CXCR4的表达能促使卵巢肿瘤细胞中发生趋化与侵袭转移的细胞数目增多,而加入CXCR4中和抗体时,能抑制上述效果。结果可见卵巢肿瘤细胞干细胞趋化因子CXCL12对SW626细胞有明显的趋化活性和侵袭转移活性,其活性是通过其受体CXCR4介导的。     

A novel chemokine receptor for SDF-1 and I-TAC involved in cell survival, cell adhesion, and tumor development

The chemokine stromal cell-derived factor (SDF-1; also known as chemokine ligand 12 [CXCL12]) regulates many essential biological processes, including cardiac and neuronal development, stem cell motility, neovascularization, angiogenesis, apoptosis, and tumorigenesis. It is generally believed that SDF-1 mediates these many disparate processes via a single cell surface receptor known as chemokine receptor 4 (CXCR4). This paper characterizes an alternate receptor, CXCR7, which binds with high affinity to SDF-1 and to a second chemokine, interferon-inducible T cell alpha chemoattractant (I-TAC; also known as CXCL11). Membrane-associated CXCR7 is expressed on many tumor cell lines, on activated endothelial cells, and on fetal liver cells, but on few other cell types. Unlike many other chemokine receptors, ligand activation of CXCR7 does not cause Ca2+ mobilization or cell migration. However, expression of CXCR7 provides cells with a growth and survival advantage and increased adhesion properties. Consistent with a role for CXCR7 in cell survival and adhesion, a specific, high affinity small molecule antagonist to CXCR7 impedes in vivo tumor growth in animal models, validating this new receptor as a target for development of novel cancer therapeutics.     

HMGB1 promotes recruitment of inflammatory cells to damaged tissues by forming a complex with CXCL12 and signaling via CXCR4

After tissue damage, inflammatory cells infiltrate the tissue and release proinflammatory cytokines. HMGB1 (high mobility group box 1), a nuclear protein released by necrotic and severely stressed cells, promotes cytokine release via its interaction with the TLR4 (Toll-like receptor 4) receptor and cell migration via an unknown mechanism. We show that HMGB1-induced recruitment of inflammatory cells depends on CXCL12. HMGB1 and CXCL12 form a heterocomplex, which we characterized by nuclear magnetic resonance and surface plasmon resonance, that acts exclusively through CXCR4 and not through other HMGB1 receptors. Fluorescence resonance energy transfer data show that the HMGB1-CXCL12 heterocomplex promotes different conformational rearrangements of CXCR4 from that of CXCL12 alone. Mononuclear cell recruitment in vivo into air pouches and injured muscles depends on the heterocomplex and is inhibited by AMD3100 and glycyrrhizin. Thus, inflammatory cell recruitment and activation both depend on HMGB1 via different mechanisms.     

Platelet‐derived CXCL12 (SDF‐1α): basic mechanisms and clinical implications

Platelets are a major source of CXCL12 (stromal cell‐derived factor ‐1α, SDF‐1α) and store CXCL12 as part of their α–granule secretome. Platelet activation enhances surface expression and release of CXCL12. Platelets and megakaryocytes express CXCR4, the major receptor for CXCL12, and interaction of CXCL12 with CXCR4 regulates megakaryopoiesis and the function of circulating platelets. Platelet‐derived CXCL12 also modulates paracrine mechanisms such as chemotaxis, adhesion, proliferation and differentiation of nucleated cells, including progenitor cells. Platelet‐derived CXCL12 enhances peripheral recruitment of progenitor cells to the sites of vascular and tissue injury both in vitro and in vivo and thereby promotes repair mechanisms. CXCL12 expression on platelets is elevated in patients with acute myocardial infarction, correlates with the number of circulating progenitor cells, is associated with preservation of myocardial function and is an independent predictor of clinical outcome. Administration of recombinant CXCL12 reduces infarct size following transient ischemia in mice. The present review summarizes the role of platelet‐derived CXCL12 in cardiovascular biology and its diagnostic and therapeutic implications.     

Neuronal ferritin heavy chain and drug abuse affect HIV-associated cognitive dysfunction

Interaction of the chemokine CXCL12 with its receptor CXCR4 promotes neuronal function and survival during embryonic development and throughout adulthood. Previous studies indicated that μ-opioid agonists specifically elevate neuronal levels of the protein ferritin heavy chain (FHC), which negatively regulates CXCR4 signaling and affects the neuroprotective function of the CXCL12/CXCR4 axis. Here, we determined that CXCL12/CXCR4 activity increased dendritic spine density, and also examined FHC expression and CXCR4 status in opiate abusers and patients with HIV-associated neurocognitive disorders (HAND), which is typically exacerbated by illicit drug use. Drug abusers and HIV patients with HAND had increased levels of FHC, which correlated with reduced CXCR4 activation, within cortical neurons. We confirmed these findings in a nonhuman primate model of SIV infection with morphine administration. Transfection of a CXCR4-expressing human cell line with an iron-deficient FHC mutant confirmed that increased FHC expression deregulated CXCR4 signaling and that this function of FHC was independent of iron binding. Furthermore, examination of morphine-treated rodents and isolated neurons expressing FHC shRNA revealed that FHC contributed to morphine-induced dendritic spine loss. Together, these data implicate FHC-dependent deregulation of CXCL12/CXCR4 as a contributing factor to cognitive dysfunction in neuroAIDS.     

CXCR7 influences leukocyte entry into the CNS parenchyma by controlling abluminal CXCL12 abundance during autoimmunity

Loss of CXCL12, a leukocyte localizing cue, from abluminal surfaces of the blood-brain barrier occurs in multiple sclerosis (MS) lesions. However, the mechanisms and consequences of reduced abluminal CXCL12 abundance remain unclear. Here, we show that activation of CXCR7, which scavenges CXCL12, is essential for leukocyte entry via endothelial barriers into the central nervous system (CNS) parenchyma during experimental autoimmune encephalomyelitis (EAE), a model for MS. CXCR7 expression on endothelial barriers increased during EAE at sites of inflammatory infiltration. Treatment with a CXCR7 antagonist ameliorated EAE, reduced leukocyte infiltration into the CNS parenchyma and parenchymal VCAM-1 expression, and increased abluminal levels of CXCL12. Interleukin 17 and interleukin 1β increased, whereas interferon-γ decreased, CXCR7 expression on and CXCL12 internalization in primary brain endothelial cells in vitro. These findings identify molecular requirements for the transvascular entry of leukocytes into the CNS and suggest that CXCR7 blockade may have therapeutic utility for the treatment of MS.     

A coordinated change in chemokine responsiveness guides plasma cell movements.

Antibody-secreting plasma cells are nonrecirculatory and lodge in splenic red pulp, lymph node medullary cords, and bone marrow. The factors that regulate plasma cell localization are poorly defined. Here we demonstrate that, compared with their B cell precursors, plasma cells exhibit increased chemotactic sensitivity to the CXCR4 ligand CXCL12. At the same time, they downregulate CXCR5 and CCR7 and have reduced responsiveness to the B and T zone chemokines CXCL13, CCL19, and CCL21. We demonstrate that CXCL12 is expressed within splenic red pulp and lymph node medullary cords as well as in bone marrow. In chimeric mice reconstituted with CXCR4-deficient fetal liver cells, plasma cells are mislocalized in the spleen, found in elevated numbers in blood, and fail to accumulate normally in the bone marrow. Our findings indicate that as B cells differentiate into plasma cells they undergo a coordinated change in chemokine responsiveness that regulates their movements in secondary lymphoid organs and promotes lodgment within the bone marrow.     

Pharmacological characterization of CXC chemokine receptor 3 ligands and a small molecule antagonist

The CXC chemokine receptor 3 (CXCR3) is predominantly expressed on T helper type 1 (Th1) cells that are involved in inflammatory diseases. The three CXCR3 ligands CXCL9, CXCL10, and CXCL11 are produced at sites of inflammation and elicit migration of pathological Th1 cells. Here, we are the first to characterize the pharmacological potencies and specificity of a CXCR3 antagonist, N-1R-[3-(4-ethoxy-phenyl)-4-oxo-3,4-dihydro-pyrido[2,3-d]pyrimidin-2-yl]-ethyl-N-pyridin-3-ylmethyl-2-(4-fluoro-3-trifluoromethyl-phenyl)-acetamide (NBI-74330), from the T487 small molecule series. NBI-74330 demonstrated potent inhibition of [(125)I]CXCL10 and [(125)I]CXCL11 specific binding (K(i) of 1.5 and 3.2 nM, respectively) and of functional responses mediated by CXCR3, such as ligand-induced guanosine 5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTPgammaS) binding, calcium mobilization, and cellular chemotaxis (IC(50) of 7 to 18 nM). NBI-74330 was selective for CXCR3 because it showed no significant inhibition of chemotactic responses to other chemokines and did not inhibit radioligand binding to a panel of nonchemokine G-protein coupled receptors. There was a striking difference in potencies among the three CXCR3 ligands, with CXCL11 > CXCL10 > CXCL9. A comparison of the rank order of K(i) values with the rank order of monocyte production levels of these three ligands revealed a precise inverse correlation, suggesting that the weaker receptor affinities of CXCL9 and CXCL10 were physiologically compensated for by an elevated expression, perhaps to maintain effectiveness of each ligand under physiological conditions.     

SI12Lymphocyte Subsets Following Autologous Transfer of CD25 Depleted Leukapheresis Products

The CXCL12/CXCR4 chemokine axis is a well characterized and important chemotactic stimulus/receptor unit that orchestrates the homing and migration of cells to the bone marrow and to ischemic tissues following tissue damage. Here, we demonstrate that the sialomucin, CD164, a regulator of haemopoietic precursor cell adhesion to stroma and entry of primitive CD34⁺CD38^lo/‐ precursor cells into cycle, modulates the migration of CD133⁺ cord blood cells to CXCL12 by associating with the CXCR4 receptor. This was demonstrated by a reduction in CD133⁺ cell migration on fibronectin to CXCL12 (i) by engaging the functional class II glycosylation‐dependent epitope on CD164 with the 103B2/9E10 class II but not the N6B6 class III antibody; and (ii) by RNAi knockdown of CD164 protein levels in CD133⁺ cells. The inhibition of migration was more pronounced in the more primitive CD34⁺CD38^lo/‐ cell subset. Similar studies using the Jurkat cell line confirmed these findings and led to further analyses using alternative chemokines. A direct association between CXCR4 and CD164 was demonstrated by the co‐localisation of CD164 with CXCR4 and VLA‐4 and VLA‐5 at the leading edge of CD133⁺ cells when CXCL12 was presented on fibronectin. This was further supported by immunoprecipitation studies that demonstrate in the absence of CXCL12, CXCR4 is associated only with VLA‐4 and VLA‐5 but on exposure to CXCL12, CD164 is rapidly recruited to the CXCR4 complex. Knock‐down of CD164 using siRNA revealed that signalling through CXCR4 via PKC‐ζ was significantly dampened. Our findings therefore support a novel association between three distinct families of cell surface receptors that regulate both cell migratory and proliferative responses and identify a CD164 as a key regulator of the CXCL12/CXCR4 axis.     

An alternatively spliced variant of CXCR3 mediates the inhibition of endothelial cell growth induced by IP-10, Mig,and I-TAC,and acts as functional receptor for platelet factor 4

The chemokines CXCL9/Mig, CXCL10/IP-10, and CXCL11/I-TAC regulate lymphocyte chemotaxis, mediate vascular pericyte proliferation, and act as angiostatic agents, thus inhibiting tumor growth. These multiple activities are apparently mediated by a unique G protein-coupled receptor, termed CXCR3. The chemokine CXCL4/PF4 shares several activities with CXCL9, CXCL10, and CXCL11, including a powerful angiostatic effect, but its specific receptor is still unknown. Here, we describe a distinct, previously unrecognized receptor named CXCR3-B, derived from an alternative splicing of the CXCR3 gene that mediates the angiostatic activity of CXCR3 ligands and also acts as functional receptor for CXCL4. Human microvascular endothelial cell line-1 (HMEC-1), transfected with either the known CXCR3 (renamed CXCR3-A) or CXCR3-B, bound CXCL9, CXCL10, and CXCL11, whereas CXCL4 showed high affinity only for CXCR3-B. Overexpression of CXCR3-A induced an increase of survival, whereas overexpression of CXCR3-B dramatically reduced DNA synthesis and up-regulated apoptotic HMEC-1 death through activation of distinct signal transduction pathways. Remarkably, primary cultures of human microvascular endothelial cells, whose growth is inhibited by CXCL9, CXCL10, CXCL11, and CXCL4, expressed CXCR3-B, but not CXCR3-A. Finally, monoclonal antibodies raised to selectively recognize CXCR3-B reacted with endothelial cells from neoplastic tissues, providing evidence that CXCR3-B is also expressed in vivo and may account for the angiostatic effects of CXC chemokines.     

趋化因子受体CXCR7在人肺癌组织和肺癌细胞系的表达

目的解析趋化因子CXCLl2第二受体CXCR7在人肺癌组织的表达模式。进一步解析cxcLl2／cxCR4／cxcR7信号通路在肺癌发生发展中的作用。方法免疫组织化学技术检测20例人肺癌组织CXCR7／CXCR4／CXCLl2的表达;免疫细胞化学分析cxcR7／CxCR4／CxcLl2在三种肺癌细胞系A549、95D和H292的表达。结果20例人肺癌组织中16例表达CXCR7,17例表达CXCR4,19例表达CXCLl2,在癌细胞的胞浆和胞膜均可观察到明显的阳性染色;正常人肺组织中仅浆细胞中等强度表达CXCR7、CXCR4和CXCLl2蛋白;A549、95D和H292三种肺癌细胞系均共表达CXCR7、CXCR4和CXCLl2蛋白。结论人肺癌组织异常表达cxcR7／CxcR4／cxcLl2,CXCR7可能也是参与肺癌发生发展的重要分子。     

子宫内膜癌组织中趋化因子CXCL12及其受体CXCR4表达水平研究

目的 观察子宫内膜癌组织中趋化因子CXCL12及其受体CXCR4表达水平,探讨其与子宫内膜癌患者临床病理特征相关性。方法 收集2012年1月～2014年12月间入院接受手术的子宫内膜癌患者52例病理标本,年龄55.6±19.2岁,以正常子宫内膜26例为对照组,年龄52.3±16.5岁。采用免疫组化技术检测趋化因子CXCL12及其受体CXCR4在子宫内膜癌组织中的表达情况,并分析它们与FIGO分期、细胞分化程度、淋巴结转移和病理类型等临床病理特征的关系。结果 CXCL12和CXCR4在子宫内膜癌组织中阳性表达率分别为76.92%和69.23%,而在正常子宫内膜组织中则分别为34.62%和30.77%,差异具有统计学意义(χ²=11.826,P＜0.01)。CXCR4的表达与子宫内膜癌细胞分化程度存在差异,有统计学意义(均P＜0.05),且与分化高低呈正相关(r=0.386,P＜0.05)。在子宫内膜癌组织中,除CXCR4表达与细胞分化程度呈正相关外,CXCL12和CXCR4表达与临床分期、淋巴结转移和病理类型无相关性(P＞0.05)。结论 CXCL12和CXCR4在子宫内膜癌组织中表达明显升高,这可能在子宫内膜癌发生发展过程中发挥重要生物学作用。     

Dimerization of CXCR4 in living malignant cells: control of cell migration by a synthetic peptide that reduces homologous CXCR4 interactions

Chemokine receptor CXCR4 (CD184) may play a role in cancer metastasis and is known to form homodimers. However, it is not clear how transmembrane regions (TM) of CXCR4 and receptor homotypic interactions affect the function of CXCR4 in living cells. Using confocal microscopy and flow cytometric analysis, we showed that high levels of CXCR4 are present in the cytoplasm, accompanied by lower expression on the cell surface in CXCR4 transfectants, tumor cells, and normal peripheral blood lymphocytes. CXCR4 homodimers were detected in tumor cells, both on the cell surface membrane and in the cytoplasm using fluorescence resonance energy transfer and photobleaching fluorescence resonance energy transfer to measure energy transfer between CXCR4-CFP and CXCR4-YFP constructs. Disruption of lipid rafts by depletion of cholesterol with methyl-beta-cyclodextrin reduced the interaction between CXCR4 molecules and inhibited malignant cell migration to CXCL12/SDF-1alpha. A synthetic peptide of TM4 of CXCR4 reduced energy transfer between molecules of CXCR4, inhibited CXCL12-induced actin polymerization, and blocked chemotaxis of malignant cells. TM4 also inhibited migration of normal monocytes toward CXCL12. Reduction of CXCR4 energy transfer by the TM4 peptide and methyl-beta-cyclodextrin indicates that interactions between CXCR4s may play important roles in cell migration and suggests that cell surface and intracellular receptor dimers are appropriate targets for control of tumor cell spread. Targeting chemokine receptor oligomerization and signal transduction for the treatment of cancer, HIV-1 infections, and other CXCR4 mediated inflammatory conditions warrants further investigation.     

人结直肠癌趋化因子配体生物轴及干细胞标志物基因表达与临床病理

背景：趋化因子配体12/趋化因子受体4生物学轴在肿瘤的特异性转移中有重要作用,而干细胞标志物糖蛋白激素受体5基因的表达对于肿瘤的增殖和侵袭转移发挥重要作用。 目的：观察趋化因子配体12/趋化因子受体4生物轴以及干细胞标志物糖蛋白激素受体5基因在人结直肠癌组织中的表达变化及其与临床中的病理特征的关系。 方法：收集2013年1至6月辽宁省肿瘤医院收治100名结直肠癌患者为实验组,100名健康体检者为对照组,采用免疫组织化学SP法检测两组组织中趋化因子配体12、趋化因子受体4及干细胞标志物糖蛋白激素受体5 mRNA表达情况,并分析趋化因子配体12、趋化因子受体4及干细胞标志物糖蛋白激素受体5 mRNA表达与结直肠癌患者年龄、性别、肿瘤大小及部位、淋巴转移以及预后等临床病理特征的相关性。 结果与结论：趋化因子受体4、糖蛋白激素受体5 mRNA在结直肠癌组织中均有较高的表达率,但是趋化因子配体12 mRNA表达率降低。趋化因子受体4、干细胞标志物糖蛋白激素受体5 mRNA、趋化因子配体12 mRNA三者与结直肠癌患者的年龄、性别等患者临床特征无相关性,与结直肠癌的发病位置及其大小也无相关性,与结直肠癌组织是否淋巴转移具有相关性关,伴有淋巴转移的结直肠癌组织中干细胞标志物糖蛋白激素受体5 mRNA和趋化因子受体4的表达率更高,而趋化因子配体12 mRNA表达无显著变化;趋化因子受体4表达随肿瘤的恶性程度增高而增高;糖蛋白激素受体5表达于胃肠道肿瘤和脑肿瘤干细胞等表面,其表达随肿瘤的恶性程度增高而增高。提示结直肠癌组织中趋化因子受体4的表达增高,糖蛋白激素受体5基因表达增高,二者增高促进了结直肠癌组织生长及转移,糖蛋白激素受体5以及趋化因子配体12/趋化因子受体4轴的表达的调控,使其或将成为肿瘤诊断及治疗的重要新靶点。     

Hypoxia-inducible factor–dependent breast cancer–mesenchymal stem cell bidirectional signaling promotes metastasis

Metastasis involves critical interactions between cancer and stromal cells. Intratumoral hypoxia promotes metastasis through activation of hypoxia-inducible factors (HIFs). We demonstrate that HIFs mediate paracrine signaling between breast cancer cells (BCCs) and mesenchymal stem cells (MSCs) to promote metastasis. In a mouse orthotopic implantation model, MSCs were recruited to primary breast tumors and promoted BCC metastasis to LNs and lungs in a HIF-dependent manner. Coculture of MSCs with BCCs augmented HIF activity in BCCs. Additionally, coculture induced expression of the chemokine CXCL10 in MSCs and the cognate receptor CXCR3 in BCCs, which was augmented by hypoxia. CXCR3 expression was blocked in cocultures treated with neutralizing antibody against CXCL10. Conversely, CXCL10 expression was blocked in MSCs cocultured with BCCs that did not express CXCR3 or HIFs. MSC coculture did not enhance the metastasis of HIF-deficient BCCs. BCCs and MSCs expressed placental growth factor (PGF) and its cognate receptor VEGFR1, respectively, in a HIF-dependent manner, and CXCL10 expression by MSCs was dependent on PGF expression by BCCs. PGF promoted metastasis of BCCs and also facilitated homing of MSCs to tumors. Thus, HIFs mediate complex and bidirectional paracrine signaling between BCCs and MSCs that stimulates breast cancer metastasis.     

In vivo-activated CD4 T cells upregulate CXC chemokine receptor 5 and reprogram their response to lymphoid chemokines.

Migration of antigen-activated CD4 T cells to B cell areas of lymphoid tissues is important for mounting T cell-dependent antibody responses. Here we show that CXC chemokine receptor (CXCR)5, the receptor for B lymphocyte chemoattractant (BLC), is upregulated on antigen-specific CD4 T cells in vivo when animals are immunized under conditions that promote T cell migration to follicles. In situ hybridization of secondary follicles for BLC showed high expression in mantle zones and low expression in germinal centers. When tested directly ex vivo, CXCR5(hi) T cells exhibited a vigorous chemotactic response to BLC. At the same time, the CXCR5(hi) cells showed reduced responsiveness to the T zone chemokines, Epstein-Barr virus-induced molecule 1 (EBI-1) ligand chemokine (ELC) and secondary lymphoid tissue chemokine (SLC). After adoptive transfer, CXCR5(hi) CD4 T cells did not migrate to follicles, indicating that additional changes may occur after immunization that help direct T cells to follicles. To further explore whether T cells could acquire an intrinsic ability to migrate to follicles, CD4(-)CD8(-) double negative (DN) T cells from MRL-lpr mice were studied. These T cells normally accumulate within follicles of MRL-lpr mice. Upon transfer to wild-type recipients, DN T cells migrated to follicle proximal regions in all secondary lymphoid tissues. Taken together, our findings indicate that reprogramming of responsiveness to constitutively expressed lymphoid tissue chemokines plays an important role in T cell migration to the B cell compartment of lymphoid tissues.     

CXCR2 and CXCR4 antagonistically regulate neutrophil trafficking from murine bone marrow

Neutrophils are a major component of the innate immune response. Their homeostasis is maintained, in part, by the regulated release of neutrophils from the bone marrow. Constitutive expression of the chemokine CXCL12 by bone marrow stromal cells provides a key retention signal for neutrophils in the bone marrow through activation of its receptor, CXCR4. Attenuation of CXCR4 signaling leads to entry of neutrophils into the circulation through unknown mechanisms. We investigated the role of CXCR2-binding ELR⁺ chemokines in neutrophil trafficking using mouse mixed bone marrow chimeras reconstituted with Cxcr2^–/– and WT cells. In this context, neutrophils lacking CXCR2 were preferentially retained in the bone marrow, a phenotype resembling the congenital disorder myelokathexis, which is characterized by chronic neutropenia. Additionally, transient disruption of CXCR4 failed to mobilize Cxcr2^–/– neutrophils. However, neutrophils lacking both CXCR2 and CXCR4 displayed constitutive mobilization, showing that CXCR4 plays a dominant role in neutrophil trafficking. With regard to CXCR2 ligands, bone marrow endothelial cells and osteoblasts constitutively expressed the ELR⁺ chemokines CXCL1 and CXCL2, and CXCL2 expression was induced in endothelial cells during G-CSF–induced neutrophil mobilization. Collectively, these data suggest that CXCR2 signaling is a second chemokine axis that interacts antagonistically with CXCR4 to regulate neutrophil release from the bone marrow.     

Transendothelial Migration of Megakaryocytes in Response to Stromal Cell-derived Factor 1 (SDF-1) Enhances Platelet Formation

Although thrombopoietin has been shown to promote megakaryocyte (MK) proliferation and maturation, the exact mechanism and site of platelet formation are not well defined. Studies have shown that MKs may transmigrate through bone marrow endothelial cells (BMEC), and release platelets within the sinusoidal space or lung capillaries. In search for chemotactic factor(s) that may mediate transmigration of MKs, we have discovered that mature polyploid MKs express the G protein–coupled chemokine receptor CXCR4 (Fusin, LESTR). Therefore, we explored the possibility that stromal cell–derived factor 1 (SDF-1), the ligand for CXCR4, may also induce transendothelial migration of mature MKs. SDF-1, but not other CXC or CC chemokines, was able to mediate MK migration (ED₅₀ = 125 pmol/liter). The MK chemotaxis induced by SDF-1 was inhibited by the CXCR4-specific mAb (12G5) and by pertussis toxin, demonstrating that signaling via the G protein–coupled receptor CXCR4 was necessary for migration. SDF-1 also induced MKs to migrate through confluent monolayers of BMEC by increasing the affinity of MKs for BMEC. Activation of BMEC with interleukin 1β resulted in a threefold increase in the migration of MKs in response to SDF-1. Neutralizing mAb to the endothelial-specific adhesion molecule E-selectin blocked the migration of MKs by 50%, suggesting that cellular interaction of MKs with BMEC is critical for the migration of MKs. Light microscopy and ploidy determination of transmigrated MKs demonstrated predominance of polyploid MKs. Virtually all platelets generated in the lower chamber also expressed CXCR4. Platelets formed in the lower chamber were functional and expressed P-selectin (CD62P) in response to thrombin stimulation. Electron microscopy of the cells that transmigrated through the BMEC monolayers in response to SDF-1 demonstrated the presence of intact polyploid MKs as well as MKs in the process of platelet formation. These results suggest that SDF-1 is a potent chemotactic factor for mature MKs. Expression of CXCR4 may be the critical cellular signal for transmigration of MKs and platelet formation.