Biomedical subjects

V Quaranta

Publications and source records attributed to V Quaranta.

At least 55 records · Page 3Linked to original sources

PubMed1995

A splice variant of alpha 6 integrin is associated with malignant conversion in mouse skin tumorigenesis.

The epithelial-specific integrin alpha 6 beta 4 is suprabasally expressed in benign skin tumors (papillomas) and is diffusely expressed in carcinomas associated with an increase in the proliferating compartment. Analysis of RNA samples by reverse transcriptase-PCR and DNA sequencing revealed that chemically or oncogenically induced papillomas (n = 8) expressed a single transcript of the alpha 6 subunit, identified as the alpha 6 A splice variant. In contrast, carcinomas (n = 13) expressed both alpha 6A and an alternatively spliced form, alpha 6B. Primary keratinocytes and a number of keratinocyte cell lines that vary in biological potential from normal skin, to benign papillomas, to well-differentiated slowly growing carcinomas exclusively expressed alpha 6A. However, I7, an oncogene-induced cell line that produces highly invasive carcinomas, expressed both alpha 6A and alpha 6B transcript and protein. The expression of alpha 6B in I7 cells was associated with increased attachment to a laminin matrix compared to cell lines exclusively expressing alpha 6A. Furthermore, introduction of an alpha 6B expression vector into a papilloma cell line expressing alpha 6A increased laminin attachment. When a papilloma cell line was converted to an invasive carcinoma by introduction of the v-fos oncogene, the malignant cells expressed both alpha 6A and alpha 6B, while the parent cell line and cells transduced with v-jun or c-myc, which retained the papilloma phenotype, expressed only alpha 6A. Comparative analysis of alpha 6B expression in cell lines and their derived tumors indicate that alpha 6B transcripts are more abundant in tumors than cell lines, and alpha 6B is expressed to a greater extent in poorly differentiated tumors. These results establish a link between malignant conversion and invasion of squamous tumor cells and the regulation of transcript processing of the alpha 6 beta 4 integrin.

Alternative Splicing↗

PubMed1995

Rapid spreading and mature hemidesmosome formation in HaCaT keratinocytes induced by incubation with soluble laminin-5r.

HaCaT cells, an immortalized keratinocyte line, incubated in plastic wells in the presence of conditioned medium from 804G cells adhered and spread rapidly in less than 30 min. In contrast, cells plated in fibroblast or keratinocyte conditioned medium adhered poorly and remained rounded at 30 min. Immunodepletion of 804G conditioned medium with polyclonal antisera to laminin-5r, but not control antisera, abolished rapid cell spreading. Electron microscopy of HaCaT cells spread by incubation in 804G conditioned medium, but not control medium, revealed mature hemidesmosomes after 24 h. Rapid spreading was also observed in wells precoated with 804G conditioned medium or 804G cell-deposited matrix, but not with fibronectin, vitronectin, or laminin-1. Immunoblotting of 804G conditioned medium with anti-laminin-5r antibodies unveiled polypeptides of 150, 140, 135, and 100 kDa, identical by electrophoretic mobility to immunoreactive polypeptides in 804G deposited matrix. Our results suggest that addition of laminin-5r in a soluble form is sufficient to promote rapid spreading and hemidesmosome assembly in keratinocytes. The mechanism of soluble laminin-5r action may include efficient surface "priming" for cell adhesion. Soluble laminin-5r may have a physiologic role in morphogenesis and repair of the epidermis and may be of use for therapeutic applications.

Animals↗

PubMed1995

Gradient of integrin alpha 6A distribution in the myocardium during early heart development.

The interactions of cells with extracellular matrices (ECM)1 are likely to be key determinants of embryonic development. Integrin adhesion receptors are ideally positioned to mediate some of these interactions since, in addition to mechanical adhesion, they transduce signals affecting cell proliferation and differentiation. We investigated expression of the integrin alpha 6 beta 1, a receptor for the ECM component, laminin in the early mouse embryo. An intriguing feature of this integrin is the existence of alpha 6 subunit isoforms. The A and B isoforms, which differ in the cytoplasmic tails, are expressed in cell-type specific fashion, and are likely to implement distinct cellular interactions with laminin. By RT-PCR, alpha 6B but not alpha 6A mRNA was detectable in embryo extracts from fertilized oocytes to 6.5 d.p.c. In subsequent stages, up to 11.5 d.p.c., alpha 6A mRNA was observed in mRNA extracts from whole embryos, but still in significantly lower amounts than alpha 6B. However, in extracts from isolated heart (9.5 to 11.5 d.p.c.), alpha 6A was the predominant alpha 6 isoform, while in extracts from other embryo parts no alpha 6A mRNA was detectable. At the protein level, immunostaining with specific antibodies showed alpha 6A protein in myocardial cells, at the early stage of heart tube development (8.5 d.p.c.). Localization to the myocardium was tightly restricted, since other structures of the embryonic heart, e.g., endocardium, or of the remaining embryo did not stain with anti-alpha 6A antibody. In the ventricular myocardium, expression of alpha 6A appeared more intense than in the subendocardial layer. Quantitation by confocal microscopy unveiled a gradient of expression of alpha 6A, increasing from the outer to the inner layers of the myocardium. This is the first demonstration of a gradient distribution of integrin molecules in a tissue, which appears to be directly connected with the process of organogenesis. The mechanism underlying our observations is not the turning on of a gene, rather it is the activation of a splicing mechanism that substitutes the cytoplasmic domain of a laminin receptor. Because integrin cytoplasmic domains are thought to be an important functional end of the molecule, this may be a mechanism to modulate cellular responses to laminin.

Animals↗

PubMed1994

A monoclonal antibody inhibits adhesion to fibronectin and vitronectin of a colon carcinoma cell line and recognizes the integrins alpha v beta 3, alpha v beta 5, and alpha v beta 6.

Using whole viable human colon carcinoma HT29 cells as immunogen, we produced a monoclonal antibody (mAb) termed 69-6-5. The antibody was functionally selected on its anti-cell-spreading activity. By immunoprecipitation of surface radiolabeled cell lysates from HT29-D4 cells (an HT29 cell clone), mAb 69-6-5 recognized a molecular complex resembling integrin heterodimers. Sequential immunodepletions with mAb to the integrin alpha v subunit demonstrated that this complex was composed of alpha v-containing integrins. Accordingly, mAb 69-6-5 reacted with integrin alpha v beta 3 immunopurified from melanoma cells and integrins alpha v beta 5 and alpha v beta 6 immunopurified from pancreatic carcinoma cells. In cell adhesion assays, the 69-6-5 mAb was able to inhibit strongly in a dose-dependent manner arginine-glycine-aspartic acid-mediated adhesion of HT29-D4 cells to vitronectin, fibronectin, or ProNectin F but not to laminin or collagen. Immunoprecipitations with beta chain-specific antisera indicated that these cells express integrins alpha v beta 5 (receptor for vitronectin) and alpha v beta 6 (receptor for fibronectin) but neither alpha v beta 1 nor alpha v beta 3. In summary, these results indicated that mAb 69-6-5 reacts with several alpha v integrins and that it can effectively interfere with the adhesive functions of at least alpha v beta 5 and alpha v beta 6, which represent the major receptors on HT29-D4 cells responsible for their adhesion on vitronectin and fibronectin.

Amino Acid Sequence↗

PubMed1994

Psoriatic lesions in patients with chronic liver disease are distinct from psoriasis vulgaris lesions, as judged on basis of integrin adhesion receptors.

Psoriatic lesions are relatively frequent in patients with chronic liver disease. Furthermore, therapy with interferons tends to exacerbate the symptoms. The pathogenesis of psoriatic lesions is unclear. An important question is whether such lesions may be linked to the underlying chronic liver disease in these patients, or whether they are incidental manifestations of psoriasis vulgaris. We collected biopsy specimens from involved and uninvolved skin areas of chronic liver disease patients with psoriatic manifestations, as well as from psoriasis vulgaris patients, and investigated the patterns of integrin adhesion receptors by means of immunohistochemical methods. Integrin expression is known to be characteristically altered in psoriasis vulgaris. We found some of these changes in chronic liver disease psoriatic lesions-namely pericellular redistribution and suprabasal expression of the basement membrane receptor alpha 6 beta 4 and of the intercellular integrins alpha 2 beta 1 and alpha 3 beta 1. However, psoriasis vulgaris causes two other typical changes: One is the induction of the prototype fibronectin receptor alpha 5 beta 1, and the other is the alteration of integrin expression in areas of the epidermis that are macroscopically normal. These two changes were not found in chronic liver disease psoriasis biopsy specimens in 14 patients investigated. Thus integrin expression may be useful in differentiating chronic liver disease psoriatic lesions from psoriasis vulgaris lesions. Even though the two types of lesions are indistinguishable on inspection or by their histological features, they may be caused by distinct pathogenetic mechanisms. It remains to be seen whether the underlying chronic liver disease has a role, albeit indirect, in such mechanisms.

Aged↗

PubMed1994

Integrin cytoplasmic domains mediate inside-out signal transduction.

We analyzed the binding of fibronectin to integrin alpha 5 beta 1 in various cells; in some cells fibronectin bound with low affinity (e.g., K562 cells) whereas in others (e.g., CHO), it bound with high affinity (Kd approximately 100 nM) in an energy-dependent manner. We constructed chimeras of the extracellular and transmembrane domains of alpha IIb beta 3 joined to the cytoplasmic domains of alpha 5 beta 1. The affinity state of these chimeras was assessed by binding of fibrinogen or the monoclonal antibody, PAC1. The cytoplasmic domains of alpha 5 beta 1 conferred an energy-dependent high affinity state on alpha IIb beta 3 in CHO but not K562 cells. Three additional alpha cytoplasmic domains (alpha 2, alpha 6A, alpha 6B) conferred PAC1 binding in CHO cells, while three others (alpha M, alpha L, alpha v) did not. In the high affinity alpha chimeras, cotransfection with a truncated (beta 3 delta 724) or mutated (beta 3(S752-->P)) beta 3 subunit abolished high affinity binding. Thus, both cytoplasmic domains are required for energy-dependent, cell type-specific affinity modulation. In addition, mutations that disrupted a highly conserved alpha subunit GFFKR motif, resulted in high affinity binding of ligands to alpha IIb beta 3. In contrast to the chimeras, the high affinity state of these mutants was independent of cellular metabolism, cell type, and the bulk of the beta subunit cytoplasmic domain. Thus, integrin cytoplasmic domains mediate inside-out signaling. Furthermore, the highly conserved GFFKR motif of the alpha subunit cytoplasmic domain maintains the default low affinity state.

Amino Acid Sequence↗

PubMed1994

Beta 4 integrin expression in myelinating Schwann cells is polarized, developmentally regulated and axonally dependent.

In developing and regenerating peripheral nerve, Schwann cells interact with axons and extracellular matrix in order to ensheath and myelinate axons. Both of these interactions are likely to be mediated by adhesion molecules, including integrins, which mediate cell-cell and cell-extracellular matrix interactions. Recently, the beta 4 integrin subunit was reported to be expressed by Schwann cells in peripheral nerve. We have examined the expression of beta 4, beta 1 and their common heterodimeric partner, the alpha 6 integrin subunit, in developing and regenerating rat peripheral nerve. beta 4 and alpha 6 are enriched in peripheral nerve and they co-localize at the abaxonal surface of myelinating Schwann cells, opposite the Schwann cell basal lamina, which contains possible ligands of alpha 6 beta 4. In contrast, beta 4 and alpha 6 are expressed in a different pattern in non-myelinating Schwann cells. The level of beta 4, but not alpha 6 or beta 1 mRNAs, increases progressively in developing nerves, reaching a peak in adult nerves well after the peak of the myelin-specific mRNAs. After axotomy, the expression of beta 4 mRNA and protein, but not alpha 6 or beta 1 mRNAs, fall rapidly but subsequently are reinduced by regenerating axons. Similarly, in cultured Schwann cells, the expression of beta 4 mRNA, but not alpha 6 mRNA, is significantly modulated by forskolin, a drug that elevates cAMP and mimics some of the effects of axonal contact. beta 4 integrin expression in Schwann cells, therefore, is regulated by Schwann cell-axon interactions, which are known to be critical in determining the Schwann cell phenotype. Furthermore, the polarized expression of alpha 6 beta 4 to the abaxonal surface of myelinating Schwann cells suggests that alpha 6 beta 4 may mediate in part the morphological changes required of Schwann cells in the process of myelination in the peripheral nervous system.

Amino Acid Sequence↗

PubMed1994

Quantitative measurement of alpha 6 beta 1 and alpha 6 beta 4 integrin internalization under cross-linking conditions: a possible role for alpha 6 cytoplasmic domains.

In epithelial cells integrins are segregated on discrete domains of the plasma membrane. Redistribution may also occur during migration or differentiation. However, little is known about the mechanisms that control such redistribution. Receptor internalization may be a part of one such mechanism. We developed a quantitative assay and measured internalization of two epithelial integrin heterodimers, alpha 6 beta 1 and alpha 6 beta 4, induced by cross-linking with specific antibodies. alpha 6 beta 1 is a receptor for EHS laminin, while alpha 6 beta 4 is a receptor for a component of the basement membrane. alpha 6 beta 4 plays an important role in the establishment of hemidesmosomes, and becomes redistributed on the epithelial cell surface when cells are in a migratory phase. We report that alpha 6 beta 4 is efficiently internalized in human keratinocytes. More than 25% of cell surface alpha 6 beta 4 was internalized at 30 minutes, after cross-linking with A9, an anti-beta 4 monoclonal antibody. alpha 6 beta 1 is also internalized, in melanoma and teratocarcinoma cells, with maximum values of 20% of total receptors expressed at the cell surface. No significant difference was observed between the alpha 6 isoforms A and B in these assays. To determine whether alpha 6 cytoplasmic domains could influence integrin endocytosis, we prepared chimeric constructs with the extracellular domain of a reporter protein (CD8), and the cytoplasmic domains of either alpha 6 A or alpha 6 B. Both alpha 6 cytoplasmic domains but not a control cytoplasmic domain promoted internalization of the chimeric proteins, after cross-linking with antibody. Internalization of alpha 6 integrins may have a role in redistributing these receptors at the cell surface. Furthermore, the cytoplasmic domains of alpha 6 may be involved in regulating integrin internalization.

Animals↗

PubMed1993

A new isoform of the laminin receptor integrin alpha 7 beta 1 is developmentally regulated in skeletal muscle.

Within the integrin family, there are two groups of receptors that bind laminin. One of these groups comprises the heterodimers alpha 3 beta 1, alpha 6 beta 1, and alpha 7 beta 1, all of which bind the E8 fragment of laminin, and whose alpha subunits show significant homology at the amino acid sequence level. alpha 3 and alpha 6 exist as isoforms with distinct cytoplasmic domains (termed A and B), suggesting that they may couple laminin adhesion to distinct cellular responses. We report the identification of a new alpha 7 mRNA which encodes an alpha 7 protein isoform with an alternative cytoplasmic domain. Based on homology with alpha 3 and alpha 6 isoforms, this new isoform is classified as alpha 7A and the previously published one as alpha 7B. This result extends the similarity between alpha 3, alpha 6, and alpha 7 laminin receptor subunits and suggests a common ancestral gene. The alpha 7 beta 1 laminin receptor was proposed to be involved in myogenic differentiation. However, alpha 7 isoforms were not investigated in that context. We detected the alpha 7B isoform mRNA in all tissues and cell types tested, including myocardial and skeletal muscle. In contrast, the alpha 7A isoform was detectable exclusively in skeletal muscle, not in myocardial muscle or cells or any other tissues or cell lines tested. Furthermore, the differentiating skeletal muscle cell line C2C12 expressed only alpha 7B at the replicating myoblast stage and acquired alpha 7A expression upon induction of differentiation and fusion. Splicing of alpha 7B mRNA in C2C12 occurred shortly after myogenin expression and could be an indicator of progression through the program of skeletal muscle differentiation.

Amino Acid Sequence↗

PubMed1993

Immunolocalization of integrins in the normal and neoplastic colonic epithelium.

Cryosections of normal colon (NC), tubular and villous adenomas (TA, VA), and variably differentiated colon adenocarcinomas (CA) were immunostained with monoclonal antibodies to alpha 1-6 and alpha v, and beta 1-4 integrin subunits; select samples were stained for cytokeratin (Ck) 20 and villin. In NC, alpha 2 staining was strongest in crypt cells; alpha 1,3 and alpha v, and beta 1,3 and beta 4, and Ck 20 and villin predominated in superficial enterocytes. In TA and VA, monolayered glands showed integrin, Ck 20 and villin patterns that differed slightly from both crypt and superficial enterocytes. Complex glands in VA showed decreased integrin staining and basal polarization; Ck 20 and villin were strong only in luminal cells. CA showed overall weaker integrin staining than adenomas. Regardless of invasion depth, well formed malignant glands mimicked TA; pleomorphic glands mimicked VA with focal basal integrin polarization and solid clusters displayed scanty integrins, uneven Ck 20, and villin in occasional cells. Diverse integrins in crypt compared with superficial enterocytes reflect changing adhesive requirements as cells migrate and terminally differentiate. Decreasing expression and altered distribution of integrins, Ck 20 and villin noted in TA, VA, and in CA of increasing grade indicate that certain adhesive and cytoskeletal features more closely relate to glandular architecture than to depth of invasion.

Adenocarcinoma↗

PubMed1992

MHC class II molecules and immunoglobulins on peripheral blood lymphocytes of the bottlenosed dolphin, Tursiops truncatus.

The immune system of marine mammals is of comparative interest because of its adaptation to the aquatic environment. Little information, however, is available on its cellular and molecular components. Here, we used a cross-reactive antibody to MHC class II molecules and an immunoglobulin-specific antiserum for identifying these molecular species on lymphocytes of the bottlenosed dolphin, Tursiops truncatus. Limited structural analyses indicated that class II molecules and immunoglobulins of dolphin closely resemble those of other vertebrates. In the peripheral blood of most land mammals both class II and immunoglobulins are usually found on B but not T lymphocytes. Expression of immunoglobulins on dolphin peripheral blood lymphocytes suggests a ratio of B cells to T cells comparable to that of land mammals. However, unlike the majority of land mammals, virtually 100% of the peripheral T cells display pronounced expression of class II molecules, generally considered an indication of T cell activation. It is therefore possible that the physiology of T cell activation has unusual attributes in the dolphin. It is especially interesting that some land mammals, namely swine (ungulates) and dogs and cats (carnivores), also express class II molecules on peripheral blood T lymphocytes. Since ungulates and carnivores are thought to share a common distant ancestry with toothed whales, the evolutionary history may be more relevant than the environmental history in determining these unusual attributes.

Animals↗

PubMed1992

Immunolocalization of integrin alpha 6 beta 4 in mouse junctional epithelium suggests an anchoring function to both the internal and the external basal lamina.

The localization of the integrin alpha 6 beta 4, a transmembrane adhesion molecule associated with hemidesmosomes, was studied in mouse junctional epithelium (JE) by the use of monoclonal antibodies in indirect immunofluorescence microscopy. The results showed that the integrin a6 subunit was expressed throughout the JE and was localized to the cell membranes, including the aspects facing the internal and external basal laminae. The beta 4 subunit had a more restricted distribution. It was expressed only in cells facing the internal and the external basal laminae and had a basally polarized distribution. In other parts of gingival epithelium, both integrin subunits were mainly expressed at the basal aspects of basal epithelial cells. The basement membrane components, type IV collagen and laminin, could be detected only in the external basal lamina and in other basement membranes of gingival epithelium. The results indicate that the a6 beta 4 integrin, expressed in mouse JE, has a role in mediating the attachment of the cells to the basement membranes facing the connective tissue and the tooth.

Animals↗

PubMed1992

Integrin distributions in renal cell carcinomas of various grades of malignancy.

We studied 41 renal cell carcinomas, classified according to histologic grades G1 through G3, by indirect immunofluorescence microscopy using a panel of monoclonal antibodies (MAb) against various integrin subunits, and the basement membrane (BM) components laminin and collagen type IV. Selected cases also were immunostained using the avidin-biotin-complex method. The alpha 3 and beta 1 integrin subunits were detected in tumor cells of all the carcinomas. All G1 carcinomas, like normal tubular epithelial cells, expressed the alpha 6 subunit, whereas it was lacking in 20% and 40% of G2 and G3 carcinomas, respectively. Furthermore, when alpha 6 was expressed, a lack of basally polarized organization of the subunit, coupled with disorganization of the BM components, correlated with histologic grade. Another feature that appeared to characterize the more anaplastic tumors was their high level (80%) of the alpha v subunit expression as compared with its absence in the G1 carcinomas. Stromal myofibroblasts, identified by double-labeling with anti-myosin, were often characterized by the expression of the alpha 1, alpha 3, alpha 5 and beta 1 subunits. These results indicate that changes in integrin expression in renal cell carcinomas may be correlated with their degree of histologic malignancy.

Basement Membrane↗

PubMed1992

An efficient and reliable method for cloning PCR-amplification products: a survey of point mutations in integrin cDNA.

A highly efficient, non-labor-intensive method for cloning DNA fragments produced by PCR amplification was used to carry out a rapid survey of potential point mutations in integrin alpha 6 cDNA from 17 different cell-type sources. The method includes glass powder purification of the PCR reaction mixture, followed by simultaneous treatment with T4 polynucleotide kinase and DNA polymerase I, and another glass powder purification. Sequences from multiple subclones of each cell type were readily generated, aligned and checked for mismatches. Several commonly used alternative procedures were compared for cloning efficiency and size-fidelity of inserted DNA fragments.

Amino Acid Sequence↗

PubMed1991

Cell type-specific integrin variants with alternative alpha chain cytoplasmic domains.

The integrin heterodimers composed of the alpha 6 subunit with the beta 1 or beta 4 subunit (alpha 6 beta 1 and alpha 6 beta 4) are receptors for laminin and basement membrane components, respectively. The alpha 3 beta 1 integrin recognizes laminin, collagen, fibronectin, or epiligrin. We report the identification of structural variants (A and B) of the alpha 6 and alpha 3 subunits, containing distinct cytoplasmic domains. The expression of one cytoplasmic domain or the other, based probably on alternative exon usage, is cell-type dependent. Most transformed cell lines express both alpha 6A and alpha 6B isoforms, as determined by mRNA amplification or antibody immunoprecipitation. In contrast, embryonic fibroblasts express exclusively alpha 6A, and embryonic stem cells express exclusively alpha 6B. In most normal tissues, both alpha 6 isoforms are detectable, but several tissues express either alpha 6A or alpha 6B. The alpha 3B mRNA was amplified from heart and brain, while all other tissues and cell lines tested contained only alpha 3A mRNA. Alternative cytoplasmic domains may provide a means for varying the cellular responses to the ligands of alpha 6 and alpha 3 integrins according to the cell type.

Amino Acid Sequence↗

PubMed1991

The internal affairs of an integrin.

Integrins are adhesion receptors that exchange signals between the extracellular and intracellular compartments. From their cell surface transmembrane location, they interact with extracellular matrix ligands or cellular counter-receptors, translating external cues into signals that affect cytoskeletal organization, cell shape and motility. Conversely, intracellular events may modify the affinities of integrins for external ligands. Inside the cell, integrins connect with cytoskeletal structures that, until recently, were thought to be exclusively actin microfilaments. We comment on the case of the epithelial integrin, alpha(6)beta(4), which may instead interact with intermediate filaments. This integrin was recently shown by several laboratories to be part of the hemidesmosome complex, an epithelial adhesive structure that is the plasma membrane anchoring site for keratin-containing intermediate filaments.

Journal Article↗

PubMed1991

Laminin receptors in the retina: sequence analysis of the chick integrin alpha 6 subunit. Evidence for transcriptional and posttranslational regulation.

The integrin alpha 6 beta 1 is a prominent laminin receptor used by many cell types. In the present work, we isolate clones and determine the primary sequence of the chick integrin alpha 6 subunit. We show that alpha 6 beta 1 is a prominent integrin expressed by cells in the developing chick retina. Between embryonic days 6 and 12, both retinal ganglion cells and other retinal neurons lose selected integrin functions, including the ability to attach and extend neurites on laminin. In retinal ganglion cells, we show that this is correlated with a dramatic decrease in alpha 6 mRNA and protein, suggesting that changes in gene expression account for the developmental regulation of the interactions of these neurons with laminin. In other retinal neurons the expression of alpha 6 mRNA and protein remains high while function is lost, suggesting that the function of the alpha 6 beta 1 heterodimer in these cells is regulated by posttranslational mechanisms.

Amino Acid Sequence↗

PubMed1991

The major laminin receptor of mouse embryonic stem cells is a novel isoform of the alpha 6 beta 1 integrin.

Laminin is the first extracellular matrix protein expressed in the developing mouse embryo. It is known to influence morphogenesis and affect cell migration and polarization. Several laminin receptors are included in the integrin family of extracellular matrix receptors. Ligand binding by integrin heterodimers results in signal transduction events controlling cell motility. We report that the major laminin receptor on murine embryonic stem (ES) cells is the integrin heterodimer alpha 6 beta 1, an important receptor for laminin in neurons, lymphocytes, macrophages, fibroblasts, platelets and other cell types. However, the cytoplasmic domain of the ES cell alpha 6 (alpha 6 B) differs totally from the reported cytoplasmic domain amino acid sequence of alpha 6 (alpha 6 A). Comparisons of alpha 6 cDNAs from ES cells and other cells suggest that the alpha 6 A and alpha 6 B cytoplasmic domains derive from alternative mRNA splicing. Anti-peptide antibodies to alpha 6 A are unreactive with ES cells, but react with mouse melanoma cells and embryonic fibroblasts. When ES cells are cultured under conditions that permit their differentiation, they become positive for alpha 6 A, concurrent with the morphologic appearance of differentiated cell types. Thus, expression of the alpha 6 B beta 1 laminin receptor may be favored in undifferentiated, totipotent cells, while the expression of alpha 6 A beta 1 receptor occurs in committed lineages. While the functions of integrin alpha chain cytoplasmic domains are not understood, it is possible that they contribute to transferring signals to the cell interior, e.g., by delivering cytoskeleton organizing signals in response to integrin engagement with extracellular matrix ligands. It is therefore reasonable to propose that the cellular responses to laminin may vary, according to what alpha subunit isoform (alpha 6 A or alpha 6 B) is expressed as part of the alpha 6 beta 1 laminin receptor. The switch from alpha 6 B to alpha 6 A, if confirmed in early embryos, could then be of striking potential relevance to the developmental role of laminin.

Amino Acid Sequence↗