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PubMed2001

Identification of novel polymorphisms in the beta7 integrin gene: family-based association studies in inflammatory bowel disease.

Linkage studies from five groups worldwide have confirmed the presence of an inflammatory bowel disease susceptibility locus on chromosome 12q. Beta 7 integrin is a strong candidate gene within this region, and is involved in lymphocyte homing to the gut and retention of intra-epithelial lymphocytes. Monoclonal antibodies to beta7 integrin ameliorate colitis in animal models. We obtained genomic sequence for beta7 integrin, and screened all 16 exons and 1.7 kb of 5' promoter region for polymorphisms in 24 individuals. Fourteen single nucleotide polymorphisms were identified in total and, of these, two common (frequency > or =10%) intronic and two amino acid changing polymorphisms were assessed for potential disease associations. Data were available from 102 multiply affected inflammatory bowel disease families (affected sibling pairs) and 362 simplex (one affected proband) families containing 254 ulcerative colitis, 13 indeterminate colitis and 300 Crohn's disease trios (parents + affected child). No significant associations with any disease phenotype were found with the transmission disequilibrium test. Beta 7 integrin is unlikely to be involved in the genetic susceptibility to inflammatory bowel disease, and therefore future studies on chromosome 12 should focus on other positional candidate genes.

Chromosome Mapping↗
PubMed2006

Coxsackie adenovirus receptor and alpha nu beta3/alpha nu beta5 integrins in adenovirus gene transfer of rat cochlea.

This study was designed to determine whether Coxsackie adenovirus receptor (CAR) and alpha nu beta3/alpha nu beta5 integrin co-receptors are involved in adenovirus gene transfer in the rat cochlea. We find that CAR and integrin co-receptors are expressed in every cell subtype transduced by the adenoviral vector Ad5 DeltaE1-E3/cytomegalovirus/green fluorescent protein (GFP) on cochlear slices in vitro. The spiral ganglion neurons, which do not express CAR, were not transduced by the virus. Blocking these receptors by monoclonal antibodies decreased transgene expression, whereas disrupting tight junctions with ethylenediaminetetraacetic acid led to an increased transgene expression. However, sensory hair cells and strial cells also expressing CAR and alpha nu integrins were not transduced by the vector. GFP expression was also studied in vivo. Perilymphatic perfusion of adenovirus in vivo did not affect hearing and only cells lining the perilymphatic spaces were transduced. Endolymphatic perfusion resulted in low-frequency hearing loss and although some cells of the organ of Corti were efficiently transduced, the sensory and the strial cells were not. Transduced sensory and strial cells were occasionally observed in cochleas after single shot of adenovirus. Pretreatment with anti-CAR and anti-alpha nu antibodies decreases GFP expression in vivo, suggesting that the CAR/alpha nu integrin pathway is involved in adenovirus transduction in the cochlea.

Action Potentials↗
PubMed2006

Implications of increased tissue transglutaminase (TG2) expression in drug-resistant breast cancer (MCF-7) cells.

The development of resistance to chemotherapeutic drugs is a major obstacle to the successful treatment of breast cancer. Ways to block or overcome this resistance are objects of intense research. We have previously shown that cancer cells selected for resistance against chemotherapeutic drugs or isolated from metastatic tumor sites have high levels of a calcium-dependent protein crosslinking enzyme, tissue transglutaminase (TG2) but no direct link between TG2 and resistance was established. As TG2 can associate with the beta members of the integrin family of proteins, we hypothesized that TG2 promotes cell survival signaling pathways by activating integrins on the surface of these cells. To test this hypothesis, we studied the expression of TG2 and its interaction with various integrins in drug-resistant MCF-7 breast cancer cells. TG2 closely associated with beta1 and beta5 integrins on the surface of drug-resistant MCF-7 (MCF-7/Dox and MCF-7/RT) cells. The incubation of TG2-expressing drug-resistant MCF-7 cells on fibronectin (Fn)-coated surfaces strongly activated focal adhesion kinase, an event that leads to the activation of several downstream signaling pathways and, in turn, can confer apoptosis-resistant phenotype to cancer cells. The role of TG2 in Fn-mediated cell attachment, cell growth, and cell survival functions was further analysed by small interfering RNA (siRNA) approach. Inhibition of TG2 by siRNA-inhibited Fn-mediated cell attachment and cell survival functions in drug-resistant MCF-7 cells. We conclude that the expression of TG2 in breast cancer cells contributes to the development of the drug-resistance phenotype by promoting interaction between integrins and Fn.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1998

cDNA cloning reveals two mouse beta5 integrin transcripts distinct in cytoplasmic domains as a result of alternative splicing.

The integrin beta5 subunit has only been found to form a heterodimer with subunit alphav which acts as a vitronectin receptor. Integrin alphavbeta5 has been implicated in cell migration and growth factor-induced angiogenesis. In the present study, a mouse liver cDNA library was screened using a human beta5 cDNA fragment obtained by reverse transcriptase PCR (RT-PCR). Three of the clones (MB5, MB15 and MB17) overlapped to give an open reading frame, called beta5A, which is homologous to the human beta5 subunit. The sequence of another clone (MB26), called beta5B, was identical with beta5A, except for a deletion of 29 bp near the 3' end of the open reading frame. The 29 bp deletion resulted in an open-reading-frame shift and a completely different C-terminal sequence in beta5B. beta5A and beta5B were shown, by RT-PCR, to be co-expressed in most mouse tissues tested, although beta5B mRNA was detected at much lower levels than beta5A. beta5A and beta5B mRNAs were also detected in the mouse monocytic cell line, J774, and in isolated mouse peritoneal macrophages. Adhesion of peritoneal macrophages has been shown to up-regulate the expression of both beta5A and beta5B mRNAs. The 29 bp sequence begins with a putative intron-splicing donor site (GTGAT...). A 3' fragment of the mouse integrin beta5 gene was cloned by PCR and sequenced showing that the 29 bp sequence was also immediately followed by an intron. Therefore, the 29 bp sequence was apparently expressed as part of the beta5A mRNA but was spliced out as part of the downstream intron in beta5B. Since the cytoplasmic domains of the integrin beta subunits are important in cytoskeleton attachment and signalling, the two alternatively spliced beta5 isoforms may have distinct roles in cell adhesion and other cellular functions.

Alternative Splicing↗
PubMed2002

beta7 Integrin expression is not required for the localization of T cells to the intestine and colitis pathogenesis.

beta7 Integrins have been shown to have an important role in the localization of T cells to the intestine. Utilizing two different experimental mouse models of inflammatory bowel disease (IBD), this study was undertaken to determine if beta7 integrin expression is critical for T cell localization to the intestine and colitis pathogenesis. Transfer of CD4+ CD45RBhigh cells into immunodeficient mice results in colitis. To examine the role of beta7 integrins, donor cells were obtained from beta7 integrin gene-deficient animals and disease induction was examined following transfer into severe combined immunodeficiency (SCID) mice. Additionally, beta7 integrin gene-deficient animals were crossed to IL-2-deficient mice and the onset of spontaneous colitis that normally occurs in IL-2-deficient animals was examined. No differences in the onset or severity of spontaneous colitis was noted in animals that were deficient in both beta7 integrin and IL-2. In contrast, the onset of colitis in recipients of T cells from beta7 integrin-deficient donors was delayed significantly. In mice receiving beta7 integrin negative cells, the initial lack of colitis appeared to correlate with fewer numbers of CD3+beta7 integrin -/- donor lymphocytes present in the host colon. The eventual development of disease, however, was associated with increased numbers of donor beta7 integrin -/- lymphocytes. These results show that beta7 integrin expression is not absolutely required for T cell localization to the intestine and colitis pathogenesis.

Adoptive Transfer↗
PubMed1996

Distribution of beta 7 integrins in human intestinal mucosa and organized gut-associated lymphoid tissue.

Two alternative integrins involved in mucosal homing (alpha 4 beta 7) or epithelial retention (alpha E beta 7) of lymphocytes were examined in the human gut. The distribution of the beta 7 subunit [monoclonal antibody (mAb) M301] was bimodal in that it was strongly expressed by alpha E beta 7 + cells but weakly by alpha 4 beta 7 + cells. More than 90% of intraepithelial lymphocytes (IEL), including the minor subsets of CD4+, T-cell receptor (TCR) gamma/delta +, and CD3- cells, expressed alpha E beta 7 as did most lamina propria CD8+ (88%) and a fraction (36%) of CD4+ lymphocytes. Conversely, B-lineage cells (CD19+) and macrophages (CD68+) were negative. In gut-associated lymphoid tissue (GALT: Peyer's patches and appendix) only a few (< 5%) cells were positive for alpha E beta 7 (confined to CD8+ lymphocytes and CD11c+ putative dendritic cells). A relatively small fraction of IEL (30-50%) expressed alpha 4 beta 7 (mAb Act-1), while most (70%) lamina propria T and B lymphocytes, blasts, plasma cells and macrophages were positive. In GALT, T lymphocytes expressed similar levels of alpha 4 beta 7 as in the lamina propria whereas relatively few B lymphocytes (< 50%) were positive. Isolated lamina propria CD8+, CD4+, CD19+, and CD38+ cells contained mRNA for alpha 4 and the former three subsets as well as appendix CD8+ cells also for beta 7 while only lamina propria CD8+ cells had mRNA for alpha E. Together, the results suggested that alpha E beta 7 and alpha 4 beta 7 are differentially regulated in inductive sites and effector sites of the human gut. Because lymphoid cells at both sites expressed mainly alpha 4 beta 7, this integrin may be a homing receptor on memory and effector cells bound for lamina propria as well as on naive lymphocytes extravasating in GALT. Conversely, because alpha E beta 7 was mainly expressed by CD8+ cells in epithelium and lamina propria, it was probably induced after extravasation, in agreement with the observation that IEL and a fraction of lamina propria T lymphocytes (mainly CD8+ cells) generally expressed higher levels of beta 7 than most CD4+ and B cells. Also a subset of putative dendritic cells located near the follicle-associated epithelium of GALT expressed alpha E beta 7, perhaps reflecting epithelial interaction during primary immune responses.

Adult↗
PubMed2002

Distinct phenotypic adhesion molecule expression on human cord blood progenitors during early Eosinophilic commitment: upregulation of beta(7) integrins.

Increasing levels of proinflammatory cells, including eosinophils and basophils, are seen at the site of allergen challenge in allergic disease of the airways. Mechanisms for the recruitment of these cell types could involve either specific upregulation of adhesion molecule and chemoattraction, or the initiation of proliferation and differentiation of inflammatory cell progenitors derived from the bone marrow. In this study, we demonstrate, in two systems of eosinophilic-basophilic lineage-committed granulocytes of relative immaturity, that eosinophilic differentiation in vivo implies the induction of a distinct adhesion phenotype, characterized by the upregulation of beta(7) integrin and downregulation of beta(1) and alpha(5) integrins. Moreover, the eosinophilic differentiation induced an upregulation of complement receptor type 1 and type 3, and the expression was further enhanced upon a short-course in vitro activation with ionomycin. These data indicate a sequential alteration of disparate members of the integrin family during eosinophilic-basophilic differentiation, which may attribute to specific adhesion requirements at distinct stages of cell maturation.

Antigens, CD↗
PubMed2001

Adhesion molecule expression in CD5-negative/CD10-negative chronic B-cell leukemias: comparison with non-Hodgkin's lymphomas and CD5-positive B-cell chronic lymphocytic leukemia.

The classification of CD5-negative/CD10-negative chronic B-cell leukemias (CD5-/CD10- CBL) can be problematic. Most of these cases may represent leukemic non-Hodgkin's lymphoma (NHL) other than B-cell chronic lymphocytic leukemia (BCLL); nonetheless, some investigators still advocate the term "CD5-negative BCLL." Because adhesion molecule (AdMol) expression patterns reflect the biology of lymphoid neoplasms, we studied a series of 106 B-cell lymphoproliferative disorders, including CD5+ BCLL (n = 56), NHL other than BCLL (n = 35), and CD5-/CD10- CBL (excluding hairy cell leukemia and prolymphocytic leukemia) with no prior history of NHL (n = 15) for expression of components of the very late antigen-4 complex (alpha4/beta1 integrin (CD49d/CD29)), components of the mucosal addressin-cell adhesion molecule receptor (alpha4(CD49d)/beta7 integrin), and L-selectin (CD62L). CD62L expression was significantly greater in CD5+ BCLL than in NHL (P < .001). Conversely, CD29, CD49d, and beta7-integrin expression were significantly greater in NHL than in CD5+ BCLL (P < .001 for each marker). These differences persisted when only blood and bone marrow samples were analyzed, with the exception of differences in CD62L expression, which approached, but did not reach, statistical significance (P = .08). The group of CD5-/CD10- CBL displayed an AdMol profile similar to NHL and was significantly different than CD5+ BCLL in expression of beta7 integrin, CD29, CD49d, and CD62L (P range < .001-.011). In summary, CD5-/CD10- CBL display an AdMol profile resembling NHL and significantly different from CD5+ BCLL, supporting the growing notion that "CD5-negative BCLL" generally represents leukemic NHL rather than a variant of true CD5+ BCLL.

Adult↗
PubMed2000

Expression of alpha(v)beta6 integrin in oral leukoplakia.

The distribution of alpha(v)beta6 integrin was examined in oral leukoplakia, lichen planus and squamous cell carcinomas using immunohistochemistry. Controls included oral mucosal wounds, chronically inflamed and normal oral mucosa. Integrins beta1, beta3, beta4, beta5, fibronectin and tenascin were also studied. The integrin alpha(v)beta6 was highly expressed throughout the whole lesion of 90% of the squamous cell carcinomas but was not present in any of the normal specimens. alpha(v)beta6 integrin was also expressed in 41% of the leukoplakia specimens, and 85% of the lichen planus samples, but in none of the tissues with inflammatory hyperplasia or chronic inflammation. The expression of beta1 integrins was localized in the basal layer, and that of the beta4 at the cell surface facing the basement membrane of all specimens. The integrins beta3 and beta5 were absent from all normal and leukoplakia specimens. Fibronectin and tenascin were present in the connective tissue underneath the epithelium of all the sections, and their expression was similar in both alpha(v)beta6-positive and alpha(v)beta6-negative tissues. A group of 28 leukoplakia patients were followed 1-4 years after first diagnosis. In this group, initially alpha(v)beta6 integrin-positive leukoplakia specimens had high tendency for disease progression while alpha(v)beta6-negative specimens did not progress. These results suggest that the expression of alpha(v)beta6 integrin could be associated in the malignant transformation of oral leukoplakias.

Antibodies, Monoclonal↗
PubMed2004

Increased primary tumor growth in mice null for beta3- or beta3/beta5-integrins or selectins.

Expression of alphavbeta3- or alphavbeta5-integrins and selectins is widespread on blood cells and endothelial cells. Here we report that human tumor cells injected s.c. into mice lacking beta3- or beta3/beta5-integrins or various selectins show enhanced tumor growth compared with growth in control mice. There was increased angiogenesis in mice lacking beta3-integrins, but no difference in structure of the vessels was observed by histology or by staining for NG2 and smooth muscle actin in pericytes. Bone marrow transplants suggest that the absence of beta3-integrins on bone marrow-derived host cells contributes to the enhanced tumor growth in beta3-null mice, although few, if any, bone marrow-derived endothelial cells were found in the tumor vasculature. Tumor growth also was affected by bone marrow-derived cells in mice lacking any one or all three selectins, implicating both leukocyte and endothelial selectins in tumor suppression. Reduced infiltration of macrophages was observed in tumors grown in mice lacking either beta3-integrins or selectins. These results implicate cells of the innate immune system, macrophages or perhaps natural killer cells, in each case dependent on integrins and selectins, in tumor suppression.

Animals↗
PubMed2003

Integrin beta cytoplasmic domain interactions with phosphotyrosine-binding domains: a structural prototype for diversity in integrin signaling.

The cytoplasmic domains (tails) of heterodimeric integrin adhesion receptors mediate integrins' biological functions by binding to cytoplasmic proteins. Most integrin beta tails contain one or two NPXYF motifs that can form beta turns. These motifs are part of a canonical recognition sequence for phosphotyrosine-binding (PTB) domains, protein modules that are present in a wide variety of signaling and cytoskeletal proteins. Indeed, talin and ICAP1-alpha bind to integrin beta tails by means of a PTB domain-NPXY ligand interaction. To assess the generality of this interaction we examined the binding of a series of recombinant PTB domains to a panel of short integrin beta tails. In addition to the known integrin-binding proteins, we found that Numb (a negative regulator of Notch signaling) and Dok-1 (a signaling adaptor involved in cell migration) and their isolated PTB domain bound to integrin tails. Furthermore, Dok-1 physically associated with integrin alpha IIb beta 3. Mutations of the integrin beta tails confirmed that these interactions are canonical PTB domain-ligand interactions. First, the interactions were blocked by mutation of an NPXY motif in the integrin tail. Second, integrin class-specific interactions were observed with the PTB domains of Dab, EPS8, and tensin. We used this specificity, and a molecular model of an integrin beta tail-PTB domain interaction to predict critical interacting residues. The importance of these residues was confirmed by generation of gain- and loss-of-function mutations in beta 7 and beta 3 tails. These data establish that short integrin beta tails interact with a large number of PTB domain-containing proteins through a structurally conserved mechanism.

Alanine↗
PubMed1996

A developmental switch in lymphocyte homing receptor and endothelial vascular addressin expression regulates lymphocyte homing and permits CD4+ CD3- cells to colonize lymph nodes.

IN adult mice, the dominant adhesion molecules involved in homing to lymph nodes are L-selectin homing receptors on lymphocytes and the peripheral lymph node addressins on specialized high endothelial venules. Here we show that, from fetal life through the first 24 hr of life, the dominant adhesion molecules are the mucosal addressin MAdCAM-1 on lymph node high endothelial venules and its counterreceptor, the Peyer's patch homing receptor, integrin alpha 4 beta 7 on circulating cells. Before birth, 40-70% of peripheral blood leukocytes are L-selectin-positive, while only 1-2% expresses alpha 4 beta 7. However, the fetal lymph nodes preferentially attract alpha 4 beta 7-expressing cells, and this can be blocked by fetal administration of anti-MAdCAM-1 antibodies. During fetal and early neonatal life, when only MAdCAM-1 is expressed on high endothelial venules, an unusual subset of CD4 + CD3- cells, exclusively expressing alpha 4 beta 7 as homing receptors, enters the lymph nodes. Beginning 24 hr after birth a developmental switch occurs, and the peripheral node addressins are upregulated on high endothelial venules in peripheral and mesenteric lymph nodes. This switch in addressin expression facilitates tissue-selective lymphocyte migration and mediates a sequential entry of different cell populations into the lymph nodes.

Animals↗
PubMed2000

Global analysis of gene expression in pulmonary fibrosis reveals distinct programs regulating lung inflammation and fibrosis.

The molecular mechanisms of pulmonary fibrosis are poorly understood. We have used oligonucleotide arrays to analyze the gene expression programs that underlie pulmonary fibrosis in response to bleomycin, a drug that causes lung inflammation and fibrosis, in two strains of susceptible mice (129 and C57BL/6). We then compared the gene expression patterns in these mice with 129 mice carrying a null mutation in the epithelial-restricted integrin beta6 subunit (beta6(-/-)), which develop inflammation but are protected from pulmonary fibrosis. Cluster analysis identified two distinct groups of genes involved in the inflammatory and fibrotic responses. Analysis of gene expression at multiple time points after bleomycin administration revealed sequential induction of subsets of genes that characterize each response. The availability of this comprehensive data set should accelerate the development of more effective strategies for intervention at the various stages in the development of fibrotic diseases of the lungs and other organs.

Animals↗
PubMed1996

Identification of a sequence within the integrin beta6 subunit cytoplasmic domain that is required to support the specific effect of alphavbeta6 on proliferation in three-dimensional culture.

The integrin alphavbeta6 augments the proliferation of epithelial cells in collagen gels and in vivo. This effect depends on the presence of a unique carboxyl-terminal region of the beta6 subunit cytoplasmic domain. In the present study, we have utilized deletional and alanine substitution mutagenesis within this region to map the amino acids responsible for alphavbeta6-mediated proliferation in more detail. Replacement or deletion of any of 6 amino acids (glutamic acid 778, lysine 779, lysine 781, valine 782, aspartic acid 783, and leucine 784) largely abolished the proliferative effects of alphavbeta6, but none of the mutants examined interfered with alphavbeta6-mediated cell adhesion or with localization of alphavbeta6 to focal adhesions. These findings suggest that residues contained within the sequence EKXKVDL are critical for the effects of alphavbeta6 on proliferation in collagen gels and that pathways initiated by interaction with this sequence are distinct from those required for integrin-mediated cell attachment or focal adhesion formation.

Alanine↗
PubMed1997

Evidence that the integrin beta3 and beta5 subunits contain a metal ion-dependent adhesion site-like motif but lack an I domain.

The amino-terminal domain of each integrin beta subunit is hypothesized to contain an ion binding site that is key to cell adhesion. A new hypothesis regarding the structure of this site is suggested by the crystallization of the I domains of the integrin alphaL and alphaM subunits (Lee, J.-O., Rieu, P., Arnaout, M. A., and Liddington, R. (1995) Cell 80, 631-638; Qu, A., and Leahy, D. J. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 10277-10281). In those proteins, an essential metal ion is bound by a metal ion-dependent adhesion site (MIDAS). The MIDAS is presented at the apex of a larger protein module called an I domain. The metal ligands in the MIDAS can be separated into three distantly spaced clusters of oxygenated residues. These three coordination sites also appear to exist in the integrin beta3 and beta5 subunits. Here, we examined the putative metal binding site within beta3 and beta5 using site-directed mutagenesis and ligand binding studies. We also investigated the fold of the domain containing the putative metal binding site using the PHD structural algorithm. The results of the study point to the similarity between the integrin beta subunits and the MIDAS motif at two of three key coordination points. Importantly though, the study failed to identify a residue in either beta subunit that corresponds to the second metal coordination group in the MIDAS. Moreover, structural algorithms indicate that the fold of the beta subunits is considerably different than the I domains. Thus, the integrin beta subunits appear to present a MIDAS-like motif in the context of a protein module that is structurally distinct from known I domains.

Amino Acid Sequence↗
PubMed1998

The human WD repeat protein WAIT-1 specifically interacts with the cytoplasmic tails of beta7-integrins.

Integrins of the beta7 subfamily, alpha4 beta7 and alphaE beta7, contribute to lymphocyte homing and to the development of protective or autoreactive immune responses at mucosal sites. The beta subunits of integrins are considered important for regulation of stimulated cell adhesion and adhesion-dependent signal transduction. Using a yeast interaction trap screen, a human WD repeat protein, termed WAIT-1, was isolated that interacts with the integrin beta7 cytoplasmic tail and is homologous to mouse EED and Drosophila ESC proteins. WAIT-1 also binds to the cytoplasmic domains of alpha4 and alphaE but not to those of integrin beta1, beta2, and alphaL subunits. Association of WAIT-1 and beta7-integrin was confirmed by coprecipitation from transiently transfected 293 cells. The binding site for WAIT-1 was mapped to a short membrane-proximal region of the beta7 cytoplasmic tail with Tyr-735 being of critical importance. Northern blot analysis revealed multiple WAIT-1-related transcripts with differential expression in circulating leukocytes, tissue-resident cells of diverse origin, and lymphoid malignancies. These results suggest that WAIT-1, together with the recently identified RACK1, may define a novel subfamily of WD repeat proteins that interact with distinct subsets of integrin cytoplasmic tails and may act as specific regulators of integrin function.

Amino Acid Sequence↗
PubMed1999

Mechanotransduction in response to shear stress. Roles of receptor tyrosine kinases, integrins, and Shc.

Shear stress, the tangential component of hemodynamic forces, activates many signal transduction pathways in vascular endothelial cells. The conversion of mechanical stimulation into chemical signals is still unclear. We report here that shear stress (12 dynes/cm2) induced a rapid and transient tyrosine phosphorylation of Flk-1 and its concomitant association with the adaptor protein Shc; these are accompanied by a concurrent clustering of Flk-1, as demonstrated by confocal microscopy. Our results also show that shear stress induced an association of alphavbeta3 and beta1 integrins with Shc, and an attendant association of Shc with Grb2. These associations are sustained, in contrast to the transient Flk-1. Shc association in response to shear stress and the transient association between alphavbeta3 integrin and Shc caused by cell attachment to substratum. Shc-SH2, an expression plasmid encoding the SH2 domain of Shc, attenuated shear stress activation of extracellular signal-regulated kinases and c-Jun N-terminal kinases, and the gene transcription mediated by the activator protein-1/12-O-tetradecanoylphorbol-13-acetate-responsive element complex. Our results indicate that receptor tyrosine kinases and integrins can serve as mechanosensors to transduce mechanical stimuli into chemical signals via their association with Shc.

Animals↗
PubMed1999

Cloning of the murine beta5 integrin subunit promoter. Identification of a novel sequence mediating granulocyte-macrophage colony-stimulating factor-dependent repression of beta5 integrin gene transcription.

We previously noted that the initial receptor by which murine osteoclast precursors bind matrix is the integrin alphav beta5 and that granulocyte-macrophage colony-stimulating factor (GM-CSF) decreases expression of this heterodimer by suppressing transcription of the beta5 gene. We herein report cloning of the beta5 integrin gene promoter and identification of a GM-CSF-responsive sequence. A 13-kilobase (kb) genomic fragment containing part of the beta5 gene was isolated by screening a mouse genomic library with a probe derived from the most 5'-end of a murine beta5 cDNA. A combination of primer extension and S1 nuclease studies identifies two transcriptional start sites, with the major one designated +1. A 1-kb subclone containing sequence -875 to + 110 is transcriptionally active in a murine myeloid cell line. This 1-kb fragment contains consensus binding sequences for basal (Sp1), lineage-specific (PU.1), and regulatable (signal transducer and activator of transcription) transcription factors. Reflecting our earlier findings, promoter activity is repressed in transfected myeloid cells treated with GM-CSF. Using deletion mutants, we localized a 109-base pair (bp) promoter region responsible for GM-CSF-inhibited beta5 transcription. We further identified a 19-bp sequence within the 109-bp region that binds GM-CSF-induced nuclear proteins by gel shift/competition assays. Mutation of the 19-bp sequence not only ablates its capacity to bind nuclear proteins from GM-CSF-treated cells, in vitro, but the same mutation, when introduced in the 1-kb promoter, abolishes its ability to respond to GM-CSF treatment. Northern analysis demonstrates that cycloheximide treatment abrogates the capacity of GM-CSF to decrease beta5 mRNA levels. In summary, we have identified a 19-bp cis-element mediating GM-CSF-induced down-regulation of beta5 by a mechanism requiring protein synthesis.

Amino Acid Sequence↗