沉默ST3Gal III抑制MDA-MB-231细胞黏附和侵袭能力

我们前期研究表明α2,3-唾液酸水平与乳腺癌侵袭转移密切相关。人α2,3-唾液酸转移酶（ST3Gal Ⅲ）可催化合成细胞表面的α2,3-唾液酸,并在乳腺癌组织中高表达,此酶活性与肿瘤转移潜能密切相关,但其机制尚未阐明。本研究中我们将继续探讨ST3Gal Ⅲ在对乳腺癌转移关键步骤粘附和侵袭中的作用。构建特异靶向ST3Gal Ⅲ的短发夹RNA（shRNA）序列的慢病毒载体,采用细胞转染沉默乳腺癌MDA-MB-231细胞的ST3Gal Ⅲ,经实时定量PCR及Western印迹检测转染后细胞ST3Gal Ⅲ mRNA及蛋白表达,验证构建了稳定下调ST3Gal Ⅲ表达的两个细胞克隆,分别记作shRNA-2、shRNA-4。细胞表面α2,3-唾液酸是ST3Gal Ⅲ下游产物,可代表酶活性。流式细胞术分析结果证实,shRNA-2、shRNA-4细胞表面α2,3-唾液酸的含量显著降低（P<0.05）。细胞黏附、细胞迁移及侵袭能力等功能学检测结果表明,shRNA细胞黏附能力及侵袭能力明显降低（P<0.05）。β1整合素表达与肿瘤侵袭能力获取密切相关。本研究中,沉默ST3Gal Ⅲ可抑制β1整合素表达（P<0.05）。这些结果提示,ST3Gal Ⅲ在乳腺癌转移关键步骤黏附和侵袭中具有重要作用,沉默ST3Gal Ⅲ抑制MDA MB-231细胞黏附和侵袭能力,其作用机制可能是通过下调β1整合素表达。此研究从新的视角认识了乳腺癌转移的机制,并可能提供乳腺癌转移治疗的新靶点。     

Depletion of alphaV integrins from osteosarcoma cells by intracellular antibody expression induces bone differentiation marker genes and suppresses gelatinase (MMP-2) synthesis.

Integrin heterodimers sharing the common alphaV subunit are receptors for adhesion glycoproteins such as vitronectin and fibronectin. They are suggested to play an essential role in cell anchoring, differentiation, and survival. Here, we describe the construction of an expression plasmid coding for an intracellular single-chain antibody against alphaV integrin subunit. Saos-2 osteosarcoma cells transfected with this DNA construct showed an approximately 70-100% decrease in the cell surface expression of alphaVbeta3 and alphaVbeta5 integrins as shown by flow cytometry. Intracellular antibody expression had no effect on the mRNA levels of alphaV integrin. Pulse chase experiments of metabolically labeled integrins showed that the translation of precursor alphaV integrin subunit was not affected. However, the maturation of alphaV integrins as glycoproteins was slow suggesting that the transport from endoplasmic reticulum to Golgi complex was partially prevented. Depletion of alphaV integrins from Saos-2 cells led to a decreased ability to spread on fibronectin and vitronectin. Furthermore, the expression of osteoblast differentiation marker genes, alkaline phosphatase and osteopontin, was induced and concomitantly the expression of matrix metalloproteinase-2 decreased. Thus, alphaV integrins seem to be important regulators of osteosarcoma cell phenotypes. Our data also indicate that the expression of intracellular antibodies is an effective strategy to study the significance of specific integrins for cell phenotype and differentiation.     

佛波酯对NIH3T3细胞整合蛋白α_5亚基表达的影响

１００ｎｍｏｌ／Ｌ佛波酯（１２－Ｏ－ｔｅｔｒａｄｅｃａｎｏｙｌｐｈｏｂｏｌ１３－ａｃｅｔａｔｅ,ＴＰＡ）作用于ＮＩＨ３Ｔ３细胞２４ｈ,流式细胞仪检测到细胞表面整合蛋白α５亚基含量增加５２．３％．Ｎｏｒｔｈｅｒｎ杂交方法测定结果亦表明整合蛋白α５亚基ｍＲＮＡ量增加,于２ｈ时达到高峰,为对照的４．１４倍．蛋白激酶Ｃ（ｐｒｏｔｅｉｎｋｉｎａｓｅＣ,ＰＫＣ）的活性增加趋势与之基本一致．运用ＰＫＣ的抑制剂鞘氨醇（ｓｐｈｉｎｇｏ－ｓｉｎｅ）和酷氨酸激酶（ｔｙｒｏｓｉｎｅｋｉｎａｓｅ,ＴＫ）抑制剂４,５,７－三羟基异黄酮（ｇｅｎｅｓｔｅｉｎ）进一步研究,发现两者均可抑制佛波酯对整合蛋白α５亚基表达的上调作用．提示佛波酯对ＮＩＨ３Ｔ３细胞整合蛋白α５亚基表达的调控与ＰＫＣ和ＴＫ均有关．     

The type I collagen induction of MT1-MMP-mediated MMP-2 activation is repressed by alphaVbeta3 integrin in human breast cancer cells.

The influence of alphaVbeta3 integrin on MT1-MMP functionality was studied in human breast cancer cells of differing beta3 integrin status. Overexpression of beta3 integrin caused increased cell surface expression of alphaV integrin and increased cellular adhesion to extracellular matrix (ECM) substrates in BT-549, MDA-MB-231 and MCF-7 cells. beta3 integrin expression also enhanced the migration of breast cancer cells on ECM substrates and enhanced collagen gel contraction. In vivo, alphaVbeta3 cooperated with MT1-MMP to increase the growth of MCF-7 cells after orthotopic inoculation in immunocompromised mice, but had no influence on in vitro proliferation. Despite these stimulatory effects, overexpression of beta3 integrin suppressed the type I collagen (Col I) induced MMP-2 activation in all breast cancer cell lines analyzed. This was also evident in extracts from the MCF-7 tumors in vivo, where MMP-2 activation was stimulated by MT1-MMP transfection, but attenuated with beta3 integrin expression. Although our studies confirm important biological effects of alphaVbeta3 integrin on enhancing cell adhesion and migration, ECM remodeling and tumor growth, beta3 integrin caused reduced MMP-2 activation in response to Col I in vitro, which appears to be physiologically relevant, as it was also seen in tumor xenografts in vivo. The reduction of MMP-2 activation (and thus MT1-MMP activity) by alphaVbeta3 in response to Col I may be important in scenarios where cells which are activated for matrix degradation need to preserve some pericellular collagen, perhaps as a substrate for cell adhesion and migration, thus maintaining a balanced level of proteolysis required for efficient tumor growth.     

Expression of alphaV and beta3 integrin subunits during implantation in pig

Integrin are adhesion molecules involved in uterine-conceptus interactions during the perimplantation period. In this study, the expression of alphaV and beta3 integrin subunits in endometrium during implantation in pigs was investigated. The immunohistochemical location was performed on paraformaldehyde-fixed, paraffin-embedded tissue sections, and the mRNA expression of alphaV was detected in endometrium. In addition, serum levels of estradiol, progesterone, follicle-stimulating hormone, and luteinizing hormone were measured on Days 0, 12, 18, and 25 of pregnancy. The results indicate that endometrium expressed integrin alphaV and beta3 in all stages examined. The most intensive staining for integrin alphaV and beta3 was observed in endometrial stroma in porcine pregnancy on Day 18. The mRNA of alphaV integrin strongly expressed on Day 18, and moderately expressed on Days 12 and 25. The correlation between serum hormone level and the mRNA expression of alphaV integrin was not significant. The expression patterns of integrin alphaV and beta3 during implantation provide insights into the important physiological function of alphaVbeta3 integrin in pig, and the strong expression of integrin alphaV and beta3 in mid-implantation may indicate its crucial role in successful implantation and embryo survival.     

Identification of physiologically relevant substrates for cloned Gal: 3-O-sulfotransferases (Gal3STs): distinct high affinity of Gal3ST-2 and LS180 sulfotransferase for the globo H backbone, Gal3ST-3 for N-glycan multiterminal Galbeta1, 4GlcNAcbeta units and 6-sulfoGalbeta1, 4GlcNAcbeta, and Gal3ST-4 for the mucin core-2 trisaccharide

Sulfated glycoconjugates regulate biological processes such as cell adhesion and cancer metastasis. We examined the acceptor specificities and kinetic properties of three cloned Gal:3-O-sulfotransferases (Gal3STs) ST-2, ST-3, and ST-4 along with a purified Gal3ST from colon carcinoma LS180 cells. Gal3ST-2 was the dominant Gal3ST in LS180. While the mucin core-2 structure Galbeta1,4GlcNAcbeta1,6(3-O-MeGalbeta1,3)GalNAcalpha-O-Bn (where Bn is benzyl) and the disaccharide Galbeta1,4GlcNAc served as high affinity acceptors for Gal3ST-2 and Gal3ST-3, 3-O-MeGalbeta1,4GlcNAcbeta1,-6(Galbeta1,3)GalNAcalpha-O-Bn and Galbeta1,3GalNAcalpha-O-Al (where Al is allyl) were efficient acceptors for Gal3ST-4. The activities of Gal3ST-2 and Gal3ST-3 could be distinguished with the Globo H precursor (Galbeta1,3GalNAcbeta1,3Galalpha-O-Me) and fetuin triantennary asialoglycopeptide. Gal3ST-2 acted efficiently on the former, while Gal3ST-3 showed preference for the latter. Gal3ST-4 also acted on the Globo H precursor but not the glycopeptide. In support of the specificity, Gal3ST-2 activity toward the Galbeta1,4GlcNAcbeta unit on mucin core-2 as well as the Globo H precursor could be inhibited competitively by Galbeta1,4GlcNAcbeta1,6(3-O-sulfoGalbeta1,3)GalNAcalpha-O-Bn but not 3-O-sulfoGalbeta1,-4GlcNAcbeta1,6(Galbeta1,3)GalNAcalpha-O-Bn. Remarkably these sulfotransferases were uniquely specific for sulfated substrates: Gal3ST-3 utilized Galbeta1,4(6-O-sulfo)-GlcNAcbeta-O-Al as acceptor, Gal3ST-2 acted efficiently on Galbeta1,3(6-O-sulfo)GlcNAcbeta-O-Al, and Gal3ST-4 acted efficiently on Galbeta1,3(6-O-sulfo)GalNAcalpha-O-Al. Mg(2+), Mn(2+), and Ca(2+) stimulated the activities of Gal3ST-2, whereas only Mg(2+) augmented Gal3ST-3 activity. Divalent cations did not stimulate Gal3ST-4, although inhibition was noted at high Mn(2+) concentrations. The fine substrate specificities of Gal3STs indicate a distinct physiological role for each enzyme.     

Altered expression pattern of integrin alphavbeta3 correlates with actin cytoskeleton in primary cultures of human breast cancer

Background

Integrins are transmembrane adhesion receptors that provide the physical link between the actin cytoskeleton and the extracellular matrix. It has been well established that integrins play a major role in various cancer stages, such as tumor growth, progression, invasion and metastasis. In breast cancer, integrin alphavbeta3 has been associated with high malignant potential in cancer cells, signaling the onset of widespread metastasis. Many preclinical breast cancer studies are based on established cell lines, which may not represent the cell behavior and phenotype of the primary tumor of origin, due to undergone genotypic and phenotypic changes. In the present study, short-term primary breast cancer cell cultures were developed. Integrin alphavbeta3 localization was studied in correlation with F-actin cytoskeleton by means of immunofluorescence and immunogold ultrastructural localization. Integrin fluorescence intensities were semi-quantitatively assessed by means of computerized image analysis, while integrin and actin expression was evaluated by Western immunoblotting.

Results

In the primary breast cancer epithelial cells integrin alphavbeta3 immunofluorescence was observed in the marginal cytoplasmic area, whereas in the primary normal breast epithelial cells it was observed in the main cell body, i.e. in the ventrally located perinuclear area. In the former, F-actin cytoskeleton appeared well-formed, consisting of numerous and thicker stress fibers, compared to normal epithelial cells. Furthermore, electron microscopy showed increased integrin alphavbeta3 immunogold localization in epithelial breast cancer cells over the area of stress fibers at the basal cell surface. These findings were verified with Western immunoblotting by the higher expression of integrin beta3 subunit and actin in primary breast cancer cells, revealing their reciprocal relation, in response to the higher motility requirements, determined by the malignant potential of the breast cancer cells.

Conclusion

A model system of primary breast cancer cell cultures was developed, in an effort to maintain the closest resembling environment to the tumor of origin. Using the above system model as an experimental tool the study of breast tumor cell behavior is possible concerning the adhesion capacity and the migrating potential of these cells, as defined by the integrin alphavbeta3 distribution in correlation with F-actin cytoskeleton.     

Pancreatic Cancer Cell Glycosylation Regulates Cell Adhesion and Invasion through the Modulation of α2β1 Integrin and E-Cadherin Function

In our previous studies we have described that ST3Gal III transfected pancreatic adenocarcinoma Capan-1 and MDAPanc-28 cells show increased membrane expression levels of sialyl-Lewis x (SLe^x) along with a concomitant decrease in α2,6-sialic acid compared to control cells. Here we have addressed the role of this glycosylation pattern in the functional properties of two glycoproteins involved in the processes of cancer cell invasion and migration, α2β1 integrin, the main receptor for type 1 collagen, and E-cadherin, responsible for cell-cell contacts and whose deregulation determines cell invasive capabilities. Our results demonstrate that ST3Gal III transfectants showed reduced cell-cell aggregation and increased invasive capacities. ST3Gal III transfected Capan-1 cells exhibited higher SLe^x and lower α2,6-sialic acid content on the glycans of their α2β1 integrin molecules. As a consequence, higher phosphorylation of focal adhesion kinase tyrosine 397, which is recognized as one of the first steps of integrin-derived signaling pathways, was observed in these cells upon adhesion to type 1 collagen. This molecular mechanism underlies the increased migration through collagen of these cells. In addition, the pancreatic adenocarcinoma cell lines as well as human pancreatic tumor tissues showed colocalization of SLe^x and E-cadherin, which was higher in the ST3Gal III transfectants. In conclusion, changes in the sialylation pattern of α2β1 integrin and E-cadherin appear to influence the functional role of these two glycoproteins supporting the role of these glycans as an underlying mechanism regulating pancreatic cancer cell adhesion and invasion.     

Expression of beta1-integrins and N-cadherin in bladder cancer and melanoma cell lines

Changes in the expression of integrins and cadherins might contribute to the progression, invasion and metastasis of transitional cell cancer of the bladder and of melanomas. The expression of alpha5 (P < 0.001), alpha2 and beta1 (P < 0.05 - P < 0.001) integrin subunits in melanoma cells from noncutaneous metastatic sites (WM9, A375) were significantly increased as compared to cutaneous primary tumor (WM35) and metastatic (WM239) cell lines. These differences might be ascribed to the invasive character of melanoma cells and their metastasis to the noncutaneous locations. The significantly heterogeneous expression of beta1 integrin subunit in two malignant bladder cancer cell lines (T24 and Hu456) and nonsignificant differences in the expression of alpha2, alpha3, and alpha5 subunits between malignant and non-malignant human bladder cell lines do not allow an unanimous conclusion on the role of these intergrin subunits in the progression of transitional cancer of bladder. The adhesion molecule, expressed in all studied melanoma and bladder cell lines, that reacted with anti-Pan cadherin monoclonal antibodies was identified as N-cadherin except in the HCV29 non-malignant ureter cell line. However, neither this nor any other bladder or melanoma cell line expressed E-cadherin. The obtained results imply that the replacement of E-cadherin by N-cadherin accompanied by a simultaneous increase in expression of alpha2, alpha3 and alpha5 integrin subunits clearly indicates an increase of invasiveness of melanoma and, to a lesser extent, of transitional cell cancer of bladder. High expression of N-cadherin and alpha5 integrin subunit seems to be associated with the most invasive melanoma phenotype.     

The selective regulation of alpha Vbeta 1 integrin expression is based on the hierarchical formation of alpha V-containing heterodimers

The integrin beta1 subunit can form a heterodimer with 12 different alpha subunits. According to the present model, the expression level of any alphabeta complex is regulated by the availability of the specific alpha subunit, whereas beta1 subunit is constantly present in a large excess. The expression of several heterodimers containing the alphaV subunit seems to be regulated by an identical mechanism. The fact that many cells express alphaVbeta1 heterodimer, and that this fibronectin/vitronectin receptor may be selectively regulated, compromises the present model of the regulation of beta1 and alphaV integrins. We have tried to solve this problem by assuming that distinct alphabeta heterodimers are formed with different tendency. To test the hypothesis, we analyzed WM-266-4 melanoma cells transfected with a cDNA construct coding for an intracellular single-chain anti-alphaV integrin antibody. We could see 70-80% reduction in the cell surface expression of alphaV subunit. However, the only one of the alphaV integrins reduced on the cell surface was alphaVbeta1. This suggests that the cell surface expression level of alphaVbeta1 is dependent on the number of alphaV subunits available after the formation of other alphaV-containing heterodimers. Thus, there seems to be a hierarchy in the complex formation between alphaV and its different beta-partners. These observations explain how alphaVbeta1 can be specifically regulated without concomitant changes in the expression of other alphaV or beta1 integrins.     

Adhesion properties of human bladder cell lines with extracellular matrix components: the role of integrins and glycosylation

Integrin subunits present on human bladder cells displayed heterogeneous functional specificity in adhesion to extracellular matrix proteins (ECM). The non-malignant cell line (HCV29) showed significantly higher adhesion efficiency to collagen IV, laminin (LN) and fibronectin (FN) than cancer (T24, Hu456) and v-raf transfected (BC3726) cell lines. Specific antibodies to the alpha(2), alpha(5) and beta(1) integrin subunits inhibited adhesion of the non-malignant cells, indicating these integrin participation in the adhesion to ECM proteins. In contrast, adhesion of cancer cells was not inhibited by specific antibodies to the beta(1) integrin subunit. Antibodies to alpha(3) integrin increased adhesion of cancer cells to collagen, LN and FN, but also of the HCV29 line with collagen. It seems that alpha(3) subunit plays a major role in modulation of other integrin receptors especially in cancer cells. Differences in adhesion to ECM proteins between the non-malignant and cancer cell lines in response to Gal and Fuc were not evident, except for the v-raf transfected cell line which showed a distinct about 6-fold increased adhesion to LN on addition of both saccharides. N-Acetylneuraminic acid inhibited adhesion of all cell lines to LN and FN irrespective of their malignancy.     

过表达外源ST3Gal I增加MCF-7细胞与胞外基质粘附和侵袭能力

为探讨过表达外源α2,3-唾液酸转移酶（ST3Gal Ⅰ）对乳腺癌MCF-7细胞粘 附和侵袭能力的影响,构建pEGFP-N1-ST3Gal I真核表达载体.采用GenEscortTM Ⅱ包裹后转染MCF-7细胞. MCF-7细胞为3组：未转染组 (M)、转染空质粒组 (P) 和转染ST3Gal I组 (ST3); 荧光显微镜观察融合蛋白EGFP ST3Gal I的表达.采用 半定量RT-PCR、Western印迹法分析转染后MCF-7细胞ST3Gal Ⅰ基因mRNA水平和 蛋白表达水平;流式细胞术分析ST3Gal Ⅰ下游产物细胞表面α2,3-唾液酸含量;采用细胞粘附实验及transwell小室检测转染前后细胞与基质胶Matrigel粘附、迁移和侵袭运动能力的变化.结果表明, 荧光显微镜下P组细胞内绿色荧光呈弥散分 布,而ST3组绿色荧光主要集中在细胞质中,RT-PCR与Western印迹也证实了外源 ST3Gal Ⅰ基因mRNA和蛋白表达均明显增加（P<0.05）,其下游产物细胞表面 α2,3-唾液酸含量明显增加（P<0.05）;与M、P组相比,ST3组表现为粘附、迁移和侵袭能力明显增强（P<0.05）.利用转染技术可明显提高外源ST3Gal Ⅰ在MCF -7细胞表达,明显增加MCF-7细胞与胞外基质（ECM）粘附、迁移和侵袭能力,可形成肿瘤入侵表型,将有望成为治疗乳腺癌转移的新靶点.     

By modulating α2β1 integrin signalling,gastrin increases adhesion oF AGS-GR gastric cancer cells

Peritoneal metastasis is a major cause of recurrence of gastric cancer and integrins are key molecules involved in gastric cancer cells attachment to the peritoneum. The peptide hormone, gastrin, initially identified for its role in gastric acid secretion is also a growth factor for gastric mucosa. Gastrin has also been shown to contribute to gastric cancers progression. Here, we provide the first evidence that gastrin increases the adhesion of gastric cancer cells. Gastrin treatment induces the expression of α2 integrin subunit through a mechanism that involves the ERK pathway. We also observed in response to gastrin an increase in the amount of α2 integrin associated with β1subunit. In addition, gastrin-stimulated cell adhesion was blocked with an anti-α2β1 integrin neutralizing antibody. We also show that gastrin activates the integrin pathway via the phosphorylation of β1 integrin by a Src family kinase. This mechanism may contribute to the enhancement of cell adhesion observed in response to gastrin since we found an inhibition of gastrin-mediated cell adhesion when cells were treated with a Src inhibitor. By regulating one of the key step of the metastatic process gastrin might contribute to increase the aggressive behaviour of human gastric tumours.     

Parathyroid hormone-related protein upregulates integrin expression via an intracrine pathway in PC-3 prostate cancer cells

Parathyroid hormone-related protein (PTHrP) is expressed by human prostatic tissue and prostate cancer cell lines, and enhances prostate tumor cell growth both in vivo and in vitro. PTHrP expression also plays a role in the development of bone metastasis, which is a frequent complication in patients with prostate carcinoma. Tumor cell adhesion to extracellular matrix (ECM) components is mediated via integrin subunits, and plays a major role in the invasion and metastasis of tumor cells. We previously showed that PTHrP overexpression increases adhesion of the human prostate cancer cell line PC-3 to the ECM molecules collagen type I, fibronectin, and laminin. Increased adhesion is accompanied by upregulation in the expression of alpha1, alpha5, alpha6, and beta4 integrin subunits. We used the same cell line to study the mechanism via which PTHrP upregulates integrin expression. Clonal PC-3 cells were established overexpressing wild-type PTHrP or PTHrP mutated in the nuclear localization sequence (NLS). Mutation of the NLS negated the effects of PTHrP on alpha1, alpha5, alpha6, and beta4 integrin expression, indicating that these effects are mediated via an intracrine pathway requiring nuclear localization. Expression of the alpha2, alpha3, alphav, and beta1 integrin subunits were comparable in wild-type and NLS-mutated PTHrP transfectants. These findings indicate that PTHrP may play a role in prostate tumor invasion and metastasis by upregulating the expression of specific integrin subunits via an intracrine pathway.     

Molecular cloning and characterization of a novel human galactose 3-O-sulfotransferase that transfers sulfate to gal beta 1-->3galNAc residue in O-glycans

We have identified a novel galactose 3-O-sulfotransferase, termed Gal3ST-4, by analysis of an expression sequence tag using the amino acid sequence of human cerebroside 3'-sulfotransferase (Gal3ST-1). The isolated cDNA contains a single open reading frame coding for a protein of 486 amino acids with a type II transmembrane topology. The amino acid sequence of Gal3ST-4 revealed 33%, 39%, and 30% identity to human Gal3ST-1, Gal beta 1-->3/4GlcNAc:-->3'-sulfotransferase (Gal3ST-2) and Gal beta 1-->4GlcNAc:-->3'-sulfotransferase (Gal3ST-3), respectively. The Gal3ST-4 gene comprised at least four exons and was located on human chromosome 7q22. Expression of Gal3ST-4 in COS-7 cells produced a sulfotransferase activity that catalyzes the transfer of [(35)S]sulfate to the C-3' position of Gal beta 1-->3GalNAc alpha 1-O-Bn. Gal3ST-4 recognizes Gal beta 1-->3GalNAc and Gal beta 1-->3(GlcNAc beta 1-->6)GalNAc as good substrates, but not Gal beta 1-->3GalNAc(OH) or Gal beta 1-->3/4GlcNAc. Asialofetuin is also a good substrate, and the sulfation was found exclusively in O-linked glycans that consist of the Gal beta 1-->3GalNAc moiety, suggesting that the enzyme is specific for O-linked glycans. Northern blot analysis revealed that 2.5-kilobase mRNA for the enzyme is expressed extensively in various tissues. These results suggest that Gal3ST-4 is the fourth member of a Gal:-->3-sulfotransferase family and that the four members, Gal3ST-1, Gal3ST-2, Gal3ST-3, and Gal3ST-4, are responsible for sulfation of different acceptor substrates.     

A role for alphaV integrin subunit in TGF-beta-stimulated osteoclastogenesis

TGF-beta increases bone resorption in vivo and greatly increases osteoclast formation stimulated by receptor activator of NF-kappaB ligand (RANKL) in vitro. TGF-beta does not independently affect the differentiation state of RAW264.7 preosteoclasts, but increases cell attachment to vitronectin. This effect is mediated by increased expression of alphaV integrin subunit mRNA and protein. Concomitant with induction of osteoclast differentiation, RANKL causes relocation of alphaV to focal sites in the cell. This effect is potentiated by TGF-beta. Integrin blockade disrupts both attachment to vitronectin and RANKL-induced osteoclast formation, but culture on vitronectin has little effect. Ectopic expression of alphaV stimulates multinucleation of RAW264.7 cells and increases the number of osteoclasts formed in the presence of RANKL. These data suggest that TGF-beta potentiates RANKL-induced osteoclast formation, in part by increased expression of the alphaV integrin subunit, which may contribute to cell fusion.     

Engagement of αIIbβ3 (GPIIb/IIIa) with ανβ3 integrin mediates interaction of melanoma cells with platelets: a connection to hematogenous metastasis

A mutual relationship exists between metastasizing tumor cells and components of the coagulation cascade. The exact mechanisms as to how platelets influence blood-borne metastasis, however, remain poorly understood. Here, we used murine B16 melanoma cells to observe functional aspects of how platelets contribute to the process of hematogenous metastasis. We found that platelets interfere with a distinct step of the metastasis cascade, as they promote adhesion of melanoma cells to the endothelium in vitro under shear conditions. Constitutively active platelet receptor GPIIb/IIIa (integrin αIIbβ3) expressed on Chinese hamster ovary cells promoted melanoma cell adhesion in the presence of fibrinogen, whereas blocking antibodies to aνβ3 integrin on melanoma cells or to GPIIb/IIIa significantly reduced melanoma cell adhesion to platelets. Furthermore, using intravital microscopy, we observed functional platelet-melanoma cell interactions, as platelet depletion resulted in significantly reduced melanoma cell adhesion to the injured vascular wall in vivo. Using a mouse model of hematogenous metastasis to the lung, we observed decreased metastasis of B16 melanoma cells to the lung by treatment with a mAb blocking the aν subunit of aνβ3 integrin. This effect was significantly reduced when platelets were depleted in vivo. Thus, the engagement of GPIIb/IIIa with aνβ3 integrin interaction mediates tumor cell-platelet interactions and highlights how this interaction is involved in hematogenous tumor metastasis.     

Integrin alphavbeta6 mediates HT29-D4 cell adhesion to MMP-processed fibrinogen in the presence of Mn2+

Mn(2+) was found to induce adhesion of HT29-D4 adenoma carcinoma cells to fibrinogen (Fb). This was independent of the expression of the beta3 integrin subunit and involved endogenous alphavbeta6 but not alphavbeta5 integrin. Thus, addition of Mn(2+) led to a change in integrin alphavbeta6 specificity. Furthermore, Mn(2+) was found to strongly activate the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) pathway in the HT29-D4 cell line. As a MAPK inhibitor strongly reduced the Mn(2+)-induced cell adhesion to Fb, it is suggested that a link between MAPK activation and cell adhesion to Fb exists. Both expression and activity of matrix metalloproteinase-9 (MMP-9) were enhanced by Mn(2+) and this led to Fb processing. MMP inhibitors prevented Mn(2+)-mediated cell adhesion to Fb, leading us to suggest that Mn(2+) promoted convergent changes in integrin alphavbeta6 conformation and Fb structure through activation of ERK/MAPK and MMP-9. Finally, we found that Mn(2+) and activators of the ERK pathway cooperated in HT29-D4 cell adhesion to Fb. Such a process may be involved in bone metastasis of some cancer cells.