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PubMed1999

Changes in the levels of integrin and focal adhesion kinase (FAK) in human melanoma cells following 532 nm laser treatment.

Despite the increase in laser therapy, concern remains that sublethal treatment of pre-malignant lesions may adversely affect the biological behaviour of surviving cells. Integrin receptors mediate interaction of cells with the extracellular matrix and their occupation leads to focal adhesion kinase (FAK) activation. Using our previously established model we have now investigated subcellular changes and compared integrin and FAK concentrations, the degree of FAK phosphorylation and its association with the beta1 integrin in laser vs. non-laser treated cells. We treated cells with laser generated from a frequency doubled Q-switched (Nd:YAG) laser system (532 nm) at 0.4 J/cm2 twice per week for 4 weeks. Using cell lysates we performed Western immunoblotting 24 hr later to detect integrin subunits and FAK proteins and immunoprecipitation to investigate FAK phosphorylation and its association with beta1. Cell morphology was examined using electron microscopy. SK23 and G361 cells exhibited an 3.4- and 11.2-fold increase, respectively, in FAK protein following laser treatment. FAK phosphorylation in SK23 cells was increased by 82%, whereas FAK phosphorylation in G361 cells was reduced slightly (2%). Furthermore, both alpha3 and 4 integrins were up-regulated, by approximately 4-fold and 7- to 9-fold, respectively. In addition, the beta1 integrin was proteolysed in both cell lines and the levels of FAK associated with beta1 was increased (2.1- and 2.7-fold, respectively). Finally, laser treatment of SK23 cells caused an increased number of cell processes. Sublethal 532 nm laser light thus induces changes in integrin and FAK concentrations and subsequently influences cellular attachment and morphology.

Cell Adhesion Molecules↗

PubMed2000

Functional activation of integrin alpha V beta 3 in tumor cells expressing membrane-type 1 matrix metalloproteinase.

Matrix metalloproteinases (MMPs) and integrins have been implicated in a variety of processes involved in tumor progression. To evaluate the individual roles of integrin alphavbeta3 and membrane-type 1 matrix metalloproteinase (MT1-MMP), as well as the effects of their joint expression on tumor cell functions, MCF7 breast carcinoma cells were transfected stably with either the MT1-MMP, the beta3 integrin subunit or both MT1-MMP and beta3 cDNAs. MT1-MMP expression is accompanied by the functional activation of integrin alphaVbeta3, thereby increasing vitronectin-mediated adhesion and migration of MCF7 cells transfected with MT1-MMP and integrin alphaVbeta3. MT1-MMP-dependent functional activation of alphaVbeta3 correlates with modification(s) of the beta3 subunit, including its higher electrophoretic mobility and affected the LM609-binding site. MCF7 cells jointly expressing MT1-MMP and alphaVbeta3 were the most efficient in adhesion to the recombinant C-terminal domain of MMP-2 as well as in generating soluble and cell surface associated mature MMP-2 enzyme. These findings suggest a mechanism of selective docking of MMP-2 at tumor cell surfaces, specifically at the sites that include MT1-MMP and activated integrin alphaVbeta3. These mechanisms may provide a link between spatial regulation of focal proteolysis by the cell surface associated MMPs and the regulation of integrin-mediated motility of tumor cells.

Antigens, CD↗

PubMed1996

Integrin-dependent signal transduction.

Integrins are receptor molecules for extracellular matrix molecules (e.g., the beta(1) family), serum components (alpha(v) family) and immunoglobulin family adhesion molecules (beta(2) family). Integrin-dependent adhesion has also been shown to have metabolic consequences. Adhesion to a variety of extracellular matrix proteins, such as fibronectin, collagen, and laminin, is a potent regulator of cell growth, differentiation, and gene expression. Ligand binding or aggregation of integrin receptors initiates a number of metabolic changes including activation of serine/threonine and tyrosine kinases, increased Ca2+ influx, increased cytoplasmic alkalinization, and altered inositol lipid metabolism. In some instances activation of transcription factors and induction of gene expression have also been demonstrated. Components of key signaling pathways involving integrins are beginning to be identified. Some studies have shown that integrins form multi-component complexes with signal transduction molecules. Elucidating the interactions of the signal transduction molecules with each other and with the integrin cytoplasmic domains will be key to understanding the initial events of signal transduction through the integrins.

Animals↗

PubMed1998

Intracellular calcium requirements for beta1 integrin activation.

Human polymorphonuclear leukocytes (PMNs) express beta1 integrins that mediate adhesion to extracellular matrix proteins following stimulation with agonists that induce an increase in intracellular calcium. The purpose of these studies was to determine the contribution made by alterations in intracellular calcium ([Ca++]i) to inside-out activation of beta1 integrins using dimethyl sulfoxide (DMSO)-differentiated granulocytic HL60 cells as a model of human PMNs. Activation of beta1 integrins was determined by measuring the expression of an activation-dependent epitope on the beta1 subunit that is recognized by monoclonal antibody (mAb) 15/7. Exposure of granulocytic HL60 cells to calcium ionophore ionomycin (800 nM) alone did not increase the binding of mAb 15/7 to the cell surface, nor did it increase beta1 integrin-mediated adhesion of the cells to fibronectin. Similarly, exposure of the cells to the direct protein kinase C (PKC) activator, dioctanoylglycerol (di-C8) at 100 microM, neither increased binding of mAb 15/7 to these cells nor adhesion to fibronectin. Simultaneous addition of di-C8 and ionomycin, however, caused a significant increase in the expression of the 15/7 epitope and cell adhesion, suggesting synergy between elevating [Ca++]i and stimulating PKC in beta1 integrin activation. Chelation of [Ca++]i with Quin-2 and EGTA reduced both basal (unstimulated) expression of the 15/7 epitope and basal adhesion of granulocytic HL60 cells to fibronectin. In addition, chelation of [Ca++]i caused a significant decrease in 15/7 binding and adhesion stimulated by low (1 ng/ml) concentrations of phorbol myristate acetate (PMA). The inhibitory effect of [Ca++]i chelation on beta1 integrin activation was reversed by repleting [Ca++]i with ionomycin in a Ca++-containing buffer, or by the addition of higher concentrations of PMA (10 ng/ml). These data suggest a role for [Ca++]i in inside-out activation of beta1 integrins, probably through a synergistic effect with PKC activation.

Antibodies, Monoclonal↗

PubMed1998

The expression of alpha 2 beta 1 integrin and alpha smooth muscle actin in fibroblasts grown on collagen.

The maturation of connective tissue involves the organization of collagen fibres by resident fibroblasts. Fibroblast attachment to collagen has been demonstrated to involve cell surface receptors, integrins of the beta 1 family. Integrins are associated with cytoplasmic actin of microfilaments either directly or through focal adhesions. The major actin isoform of fibroblast microfilaments is beta actin and to a lesser extent alpha smooth muscle (alpha SM) actin. Cultured human dermal fibroblasts derived from adult dermis, newborn foreskin or keloid scar were grown on either uncoated or collagen-coated surfaces. The expression and synthesis of both alpha 2 beta 1 integrin and alpha SM actin were followed by immunohistology and immunoprecipitation. Fibroblasts on uncoated surfaces expressed little alpha 2 beta 1 integrin on their surface, while 20 per cent of them demonstrated alpha SM actin within microfilaments. Fibroblasts grown on a collagen-coated surface minimally expressed alpha SM actin in microfilament structures and a majority of the cells were positive for alpha 2 beta 1 integrin on their membranes. Using [35S]-methionine incorporation and immunoprecipitation, it was shown that fibroblasts grown in uncoated dishes synthesized more alpha SM actin than fibroblasts grown on collagen-coated dishes. In contrast, fibroblasts grown on collagen coated dishes synthesized more alpha 2 beta 1 integrin compared to the same cells grown on uncoated dishes. Fibroblasts maintained on a type I collagen upregulate the expression and synthesis of alpha 2 beta 1 integrin, and downregulate the expression and synthesis of alpha SM actin.

Actins↗

PubMed1998

Pyk2 is differentially regulated by beta1 integrin- and CD28-mediated co-stimulation in human CD4+ T lymphocytes.

Beta1 integrins can provide T cell co-stimulation, but little is known concerning their downstream signaling pathways. We found that Pyk2, a focal adhesion kinase-related tyrosine kinase, is regulated by beta1 integrin signaling in human T cells. Stimulation of Jurkat T cells with the alpha4beta1 integrin ligand VCAM-1 results in Pyk2 tyrosine phosphorylation, and combined stimulation with VCAM-1 and anti-CD3 mAb induces rapid and sustained synergistic Pyk2 phosphorylation. Studies with mAb suggest that in synergistic CD3- and alpha4beta1 integrin-mediated Pyk2 tyrosine phosphorylation, a major contribution of CD3-derived signals is independent of their effects on regulating integrin adhesion. Analysis of resting human CD4+ T cells confirmed the ability of CD3-derived signals to synergize with beta1 integrin-dependent signals in the induction of Pyk2 tyrosine phosphorylation. In addition, although CD28-mediated co-stimulatory signals were able to synergize with CD3-mediated signals in inducing ERK and JNK activation and secretion of IL-2 in the primary T cells, they did not contribute to the induction of Pyk2 phosphorylation. Taken together, these results indicate a potential role for Pyk2 in T cell co-stimulation mediated specifically by beta1 integrins.

CD28 Antigens↗

PubMed2002

Induction of cell death in T lymphocytes by invasin via beta1-integrin.

Ligand binding to beta1-integrins exerts multiple effects on cells of the immune system including adhesion, spreading, haptotaxis and costimulation of T cells activated by anti-CD3. Here we show that a high-affinity ligand for beta1-integrins, the invasin (Inv) protein of Yersinia pseudotuberculosis, can induce cell death in T lymphocytes via a rapid process. Partially purified native Inv protein and an Inv fusion protein caused apoptotic/necrotic caspase-independent cell death in T lymphocytes as determined by phosphatidylserine exposure on the cell surface, uptake of propidium iodide, labeling of DNA strand breaks and presence of DNA ladder. Inv-induced cell death was mediated via beta1-integrins as indicated by the fact that Inv bound to the beta1-integrin subunit (CD29), that anti-beta(1)-integrin antibodies blocked Inv-induced cell death and that Inv-induced cell death was absent in two beta1-integrin- cell lines produced by different procedures. Killing via beta1-integrins represents a novel pathway for cell death in T lymphocytes.

Adhesins, Bacterial↗

PubMed2002

Beta 1 integrin activation mediates adhesive differences between trisomy 21 and non-trisomic fibroblasts on type VI collagen.

Trisomy 21 (Down syndrome) is a common genetic condition with a high incidence of congenital heart defects (CHD), particularly those involving abnormal development of the embryonic atrioventricular (AV) canal. Type VI collagen (Col VI) is expressed in the developing AV canal extracellular matrix, and has been associated with trisomy 21 AV canal defects in human genetic studies. Although the molecular mechanisms linking Col VI and trisomy 21 AV canal defects are not well understood, a computer model predicts increased cell adhesiveness is responsible for these CHD. We compared integrin-mediated cell adhesive properties for skin fibroblasts isolated from trisomy 21 and non-trisomic individuals on Col VI, fibronectin (FN) and type I collagen (Col I). Cell lines demonstrate similar adhesion profiles to FN and Col I, but all trisomy 21 cells display increased adhesive capacity for Col VI compared to non-trisomic fibroblasts. Cell adhesion to type VI collagen was shown to be GRGDS independent, but beta(1) integrin family dependent. Function-blocking antibodies identified alpha(3)beta(1) as the predominant integrin mediating trisomy 21 and non-trisomic skin fibroblast adhesion on Col VI. Trisomy 21 and non-trisomic fibroblasts display similar expression levels for each of the integrin receptors examined. A beta(1) integrin-activating antibody augments non-trisomic cell adhesion on Col VI, but has no effect upon trisomy 21 fibroblasts. These results demonstrate that beta(1) integrin family members mediate trisomy 21 and non-trisomic skin fibroblast adhesion for Col VI. Altered activation state of the beta(1) integrin is a mechanism responsible for increased trisomy 21 cell adhesion on Col VI.

Cell Adhesion↗

PubMed1995

Integrin and phosphotyrosine expression in normal and migrating newt keratinocytes.

BACKGROUND: Cells interact with the extracellular matrix through a family of cell surface receptors known as integrins. Ligand specificity of a given integrin is determined in part by the type of alpha and the type of beta subunit comprising it. Accumulating evidence suggests that integrin-ligand binding in some systems influences cell behavior through tyrosine phosphorylation of intracellular proteins. METHODS: In this study, we utilized immunohistochemistry to examine the expression of beta 1 and beta 4 integrin subunits as well as tyrosine phosphorylation in normal keratinocytes and in keratinocytes migrating to form a wound epithelium. An adhesion assay was used to determine if freshly isolated keratinocytes could interact with fibronectin and collagen. Polyacrylamide gel electrophoresis followed by immunoblotting was employed to compare beta 1 integrins in migrating and nonmigrating keratinocytes. RESULTS: In normal epidermis, beta 1 and beta 4 localized primarily to basal cells, where both subunits were generally distributed over all parts of the cell periphery. Except for a modest presence in suprabasal cells and a minimal presence adjacent to the epidermal basement membrane, phosphotyrosine (ptyr) had a similar distribution. In migrating keratinocytes, beta 1, beta 4, and ptyr localized most heavily at the interface between the forming wound epithelium and the wound bed. Adhesion assays using keratinocytes from normal epidermis revealed a population of cells that could specifically adhere and spread on fibronectin and type I collagen. Immunoblots of beta 1 subunits from normal and migrating keratinocytes showed no increase in amount of beta 1, nor did the apparent size of beta 1 change in migrating compared to normal cells. CONCLUSIONS: The heavy accumulation of beta 1 and beta 4 at the wound bed interface in migrating cells suggests that these subunits may be involved in attachments of migrating cells to extracellular matrix proteins in the wound. The accumulation of ptyr in the same region further suggests that integrin-ligand interaction in keratinocytes modulates cell behavior through phosphorylated proteins. The fact that freshly isolated newt keratinocytes could adhere and spread on fibronectin or collagen shows that these cells are constitutively activated. This view is supported by the absence of any evidence that the beta 1 in migrating keratinocytes is larger and therefore more mature than beta 1 in normal keratinocytes. By comparison, beta 1 integrins on human keratinocytes are not constitutively activated (Takashima and Grinnell, 1985; Toda et al., 1987; Guo et al., 1990, 1991), a difference that may explain why epidermal wound healing is faster in newts than in humans.

Animals↗

PubMed1992

Elevated expression of beta 1 and beta 2 integrins, intercellular adhesion molecule 1, and endothelial leukocyte adhesion molecule 1 in the skin of patients with systemic sclerosis of recent onset.

OBJECTIVE: To investigate the possible role of integrins and cell adhesion molecules in the pathogenesis of the mononuclear cell infiltration and fibrosis of skin that occurs in systemic sclerosis (SSc). METHODS: The presence and topographic distribution of beta 1, beta 2, and beta 4 integrins, as well as of endothelial leukocyte adhesion molecule 1 (ELAM-1) and intercellular adhesion molecule 1 (ICAM-1), was examined immunohistochemically in affected skin from 8 patients with rapidly progressive SSc of recent onset. The expression of the beta 1 integrin gene was also investigated by in situ hybridization with a human sequence-specific complementary DNA. RESULTS: The presence of beta 1 integrin epitopes and the corresponding messenger RNA within inflammatory cells surrounding small vessels was demonstrated in SSc skin but not in normal skin. Lymphocytes positive for beta 2 integrin were also found only in SSc skin, and they appeared in close proximity to small blood vessels and collagen bundles. Immunostaining for beta 4 integrin epitopes revealed no differences between normal and SSc skin. ELAM-1 and ICAM-1 monoclonal antibodies, which identify epitopes indicative of endothelial cell activation, stained endothelial cells in SSc skin but not normal skin. CONCLUSION: These observations suggest that the complex interactions of beta 1 and beta 2 integrins, as well as ELAM-1 and ICAM-1, may be intimately involved in the pathogenesis of SSc, perhaps by mediating the homing and targeting of pathogenetic lymphocytes to the affected tissues.

Antibodies, Monoclonal↗

PubMed1993

Integrin-mediated attachment of articular chondrocytes to extracellular matrix proteins.

OBJECTIVE: To investigate the interactions between chondrocytes and their extracellular matrix (ECM). An attachment assay was used to determine the extent of integrin-mediated attachment of chondrocytes to a variety of ECM proteins and the effect of monolayer culturing on attachment activity. METHODS: Bovine and human articular cartilage chondrocytes were grown in high-density monolayer cultures for 3-21 days and used in the assays. Cell shape and production of 3H-proline-labeled collagen were monitored to assess phenotypic changes with time in culture. Cultured chondrocytes were incubated in wells coated with purified proteins, with and without specific inhibitors of integrin-mediated attachment, and cell attachment was determined. RESULTS: Compared with bovine serum albumin, chondrocytes showed significant attachment to fibronectin, matrix Gla protein (MGP), osteopontin, bone sialoprotein II (BSP II), vitronectin, and types II and VI collagen. A synthetic peptide containing the integrin-recognition sequence Arg-Gly-Asp inhibited attachment to all the proteins tested, except types II and VI collagen. A monoclonal antibody (MAb) to the beta 1-integrin subunit inhibited attachment to fibronectin, MGP, and type II collagen, and a MAb to the beta 3-integrin subunit inhibited attachment to BSP II and osteopontin. An increase in cell attachment was seen with time in culture, and this increase was followed by a change in the chondrocytes to flattened, type I collagen-producing cells. CONCLUSION: Chondrocytes can attach to a variety of cartilage and bone proteins; this attachment is mediated via integrins, including members of both the beta 1 and beta 3 subunit families. The modulation of the chondrocyte phenotype during monolayer culture may be related to activation or increased expression of integrins.

Animals↗

PubMed1994

Integrin expression by human articular chondrocytes.

OBJECTIVE: To perform a comprehensive analysis of the integrin forms expressed by normal human articular chondrocytes. METHODS: Cartilage sections and collagenase-released chondrocytes were probed with a comprehensive panel of integrin isoform-specific monoclonal antibodies (MAb), using in situ immunohistochemistry techniques, indirect immunofluorescence and flow cytometry, and immunoprecipitation/sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). RESULTS: Chondrocytes in cartilage sections reacted with MAb specific for the alpha 5, alpha v, and beta 1 integrin subunits and the alpha v beta 3 and alpha v beta 5 heterodimers. They also reacted with a polyclonal antibody specific for the intracytoplasmic portion of the alpha 1 subunit. MAb specific for the alpha v subunit reacted more strongly with chondrocytes near the articular surface than with those in deeper layers of cartilage, and the alpha v beta 3-specific MAb reacted exclusively with chondrocytes within the most superficial 30 microns of cartilage. Flow cytometric analysis and SDS-PAGE analysis of immunoprecipitates prepared from extracts of cell-surface radioiodinated chondrocytes confirmed the above observations, and additionally revealed the presence of the alpha 3 beta 1 integrin. CONCLUSION: Normal human articular chondrocytes prominently display substantial quantities of the alpha 1 beta 1, alpha 5 beta 1, and alpha v beta 5 integrin heterodimers, as well as lesser quantities of the alpha 3 beta 1 and alpha v beta 3 heterodimers. The alpha v subunit-containing integrins are detected more readily on the more superficial chondrocytes than on chondrocytes deep within cartilage. These observations provide the basis for analysis of the role of chondrocyte integrins in cartilage homeostasis and in the pathogenesis of joint diseases.

Adult↗

PubMed1993

Integrins hold Drosophila together.

The Drosophila position-specific (PS) integrins are members of the integrin family of cell surface receptors and are thought to be receptors for extracellular matrix components. Each PS integrin consists of an alpha subunit, alpha PS1 or alpha PS2, and a beta PS subunit. Mutations in the beta PS subunit and the alpha PS2 subunit have been characterised and reveal that the PS integrins have an essential role in the adhesion of different cell layers to each other. The PS integrins are especially required for the function of the cell-matrix-cell junctions, where the muscles attach to the epidermis and where one surface of the developing wing adheres to the other. These junctions are similar to vertebrate focal adhesions and hemidesmosomes, which also contain integrins. Integrin-mediated cell to cell adhesion via the extracellular matrix provides a way for tissues to adhere to each other without intermingling of their cells.

Animals↗

PubMed1995

Signal transduction through integrins: a central role for focal adhesion kinase?

The integrins are receptors for proteins of the extracellular matrix, both providing a physical link to the cytoskeleton and transducing signals from the extracellular matrix. Activation of integrins leads to tyrosine and serine phosphorylation of a number of proteins, elevation of cytosolic calcium levels, cytoplasmic alkalinization, changes in phospholipid metabolism and, ultimately, changes in gene expression. The recently discovered focal adhesion kinase localizes to focal contacts, which are sites of integrin clustering, and focal adhesion kinase can physically associate with integrins in vitro. As integrins lack intrinsic catalytic activity, focal adhesion kinase is a candidate for a signaling molecule that is recruited by integrins in order to trigger the generation of intracellular second messengers. Thus, focal adhesion kinase may play a central role in signal transduction through integrins.

Cell Adhesion↗

PubMed2005

Integrin activation and neurotrophin signaling cooperate to enhance neurite outgrowth in sensory neurons.

Neurite growth is influenced by many factors, including the availability of trophic support as well as the extracellular environment. In this study, we have investigated whether attachment to a permissive culture substrate such as laminin is sufficient to promote neurite outgrowth from dorsal root ganglion neurons in the absence of added nerve growth factor (NGF) and whether this attachment can enhance the response of these neurons to NGF. Adult dorsal root ganglia neurons plated on surfaces coated with a thin film of laminin exhibited increased neurite outgrowth. This effect was integrin-dependent as it was attenuated by treatment with RGD (arginine-glycine-aspartate) peptides and by a beta1-integrin blocking antibody. The addition of NGF resulted in a significant increase in the integrin-dependent outgrowth. We have correlated this increase in growth with increased expression of integrin subunits and activation of known downstream signaling intermediates such as focal adhesion kinase, Src, and Akt. We have also examined pathway cooperation through the use of an Src-specific inhibitor, PP2, and a beta1-integrin blocking antibody, beta1i, by observing downstream signaling intermediates in both integrin and growth factor signaling pathways. These results are among the first to detail the importance of interactions between neurotrophin- and integrin-activated signaling in adult primary neurons.

Animals↗

PubMed1992

Modulation of integrin expression during mast cell differentiation.

Previously we have reported that rodent mast cells synthesize the mRNA encoding the alpha and beta integrin chains (alpha 4, beta 1 and beta 7) of the lymphocyte Peyer's patch adhesion molecule (LPAM)-1 and LPAM-2 lymphocyte homing receptors, and that they possess an alpha 4-containing integrin complex on their cell surface. In this report, we have examined the expression of these integrin chain genes by mature connective tissue mast cells (CTMC) and by bone marrow-derived mast cells (BMMC) differentiated from bone marrow precursor cells in the presence of interleukin (IL)-3 and/or the c-kit ligand (also known as mast cell growth factor and stem cell growth factor). High levels of both the beta 7 and beta 1 transcripts were present in mature CTMC while those encoding the alpha 4 chain were absent. Similarly, when BMMC were grown in IL-3 for 28 days and analyzed for integrin chain transcripts, those specific for the alpha 4 chain were also diminished compared to beta 7 and beta 1 transcripts. To compare the expression of these integrin genes during mucosal mast cell and CTMC development, BMMC were derived in the presence of IL-3 alone, c-kit alone, or IL-3/c-kit together. These experiments indicated that c-kit inhibited the transcription of the beta 7 and Fc epsilon RI genes while enhancing alpha 4 transcript levels. The enhancement of alpha 4 levels, however, was abrogated with the addition of IL-3. Similarly, the c-kit-induced depression of beta 7 and Fc epsilon RI transcript levels was overcome by the addition of IL-3. These data suggest that the integrin complexes synthesized by the mast cells may differ depending upon their path of differentiation and that another alpha chain integrin may be synthesized to complex with the beta 7 and/or beta 1 chains.

Animals↗

PubMed2005

Involvement of beta1 integrin in microglial chemotaxis and proliferation on fibronectin: different regulations by ADP through PKA.

Microglia are immune cells in the brain; their activation, migration, and proliferation have pivotal roles in brain injuries and diseases. Microglia are known to attach firmly to fibronectin, the upregulation of which is associated with several pathological conditions in the CNS, through beta1 integrin and become activated. Extracellular nucleotides can serve as potent signaling molecules. Recently, ATP and ADP were revealed to possess chemoattractive properties to microglia via Gi-coupled P2Y receptors. In the present study, we report that the ADP-induced chemotaxis of microglia is mediated by P2Y12/13 receptors and is beta1 integrin-dependent in the presence of fibronectin. Signals from P2Y12/13 receptors also cause beta1 integrin translocation to the membrane ruffle regions, but this redistribution was lost when the intracellular cyclic AMP (cAMP) was increased by forskolin or dibutyryl cAMP. This inhibitory effect of cAMP-elevating agents did not appear when microglia were co-incubated with a protein kinase A (PKA) inhibitor, KT-5720, suggesting that PKA is a negative regulator of the beta1 integrin translocation. We also show that the engagement of beta1 integrin enhanced microglial proliferation. Signals from P2Y12/13 receptors attenuated the proliferation, whereas ADP itself had no effect on microglial growth. Furthermore, beta1 integrin-induced proliferation is positively regulated by the cAMP-dependent PKA. Together, these results indicate the involvement of beta1 integrin in microglial proliferation and chemotaxis, both of which have clinical importance. The data also suggest that PKA is inversely involved in these two cellular functions.

Adenosine Diphosphate↗

PubMed2002

Association between alphavbeta6 integrin expression, elevated p42/44 kDa MAPK, and plasminogen-dependent matrix degradation in ovarian cancer.

Altered expression of alphav integrins plays a critical role in tumor growth, invasion, and metastasis. In this study, we show that normal human epithelial ovarian cell line, HOSE, and ovarian cancer cell lines, OVCA 429, OVCA 433, and OVHS-1, expressed alphav integrin and associated beta1, beta3, and beta5 subunits, but only ovarian cancer cell lines OVCA 429 and OVCA 433 expressed alphavbeta6 integrin. The expression of alphavbeta6 in OVCA 429 and OVCA 433 was far higher than alphavbeta3 and alphavbeta5 integrin and correlated with high p42/p44 mitogen activated protein kinase (MAPK) activity and high secretion of high molecular weight urokinase plasminogen activator (HMW-uPA), pro-metalloproteinase 2 and 9 (pro-MMP-9 and pro-MMP-2). In contrast to HOSE and OVHS 1, OVCA 433 and OVCA 429 exhibited approximately 2-fold more plasminogen-dependent [3H]-collagen type IV degradation. Plasminogen-dependent [3H]-collagen IV degradation was inhibited by inhibitor of uPA (amiloride) and MMP (phenanthroline) and by antibodies against uPA or MMP-9 or alphavbeta6 integrin, indicating the involvement of alphavbeta6 integrin, uPA and MMP-9 in the process. The alphavbeta6 correlated increase in HMW-uPA and pro-MMP secretion could be inhibited by tyrosine kinase inhibitor genistein or the MEK 1 inhibitor U0126, consistent with a role of active p42/44 MAPK in the elevation of uPA, MMP-9, and MMP-2 secretion. Under similar conditions, genistein and U0126 inhibited plasminogen-dependent [3H]-collagen type IV degradation. These data suggest that sustained elevation of p42/44 MAPK activity may be required for the co-expression of alphavbeta6 integrin, which in turn may regulate the malignant potential of ovarian cancer cells via proteolytic mechanisms.

Antigens, Neoplasm↗