Distinct molecular interactions mediate neuronal process outgrowth on non-neuronal cell surfaces and extracellular matrices.

We have compared neurite outgrowth on extracellular matrix (ECM) constituents to outgrowth on glial and muscle cell surfaces. Embryonic chick ciliary ganglion (CG) neurons regenerate neurites rapidly on surfaces coated with laminin (LN), fibronectin (FN), conditioned media (CM) from several non-neuronal cell types that secrete LN, and on intact extracellular matrices. Neurite outgrowth on all of these substrates is blocked by two monoclonal antibodies, CSAT and JG22, that prevent the adhesion of many cells, including neurons, to the ECM constituents LN, FN, and collagen. Neurite outgrowth is inhibited even on mixed LN/poly-D-lysine substrates where neuronal attachment is independent of LN. Therefore, neuronal process outgrowth on extracellular matrices requires the function of neuronal cell surface molecules recognized by these antibodies. The surfaces of cultured astrocytes, Schwann cells, and skeletal myotubes also promote rapid process outgrowth from CG neurons. Neurite outgrowth on these surfaces, though, is not prevented by CSAT or JG22 antibodies. In addition, antibodies to a LN/proteoglycan complex that block neurite outgrowth on several LN-containing CM factors and on an ECM extract failed to inhibit cell surface-stimulated neurite outgrowth. After extraction with a nonionic detergent, Schwann cells and myotubes continue to support rapid neurite outgrowth. However, the activity associated with the detergent insoluble residue is blocked by CSAT and JG22 antibodies. Detergent extraction of astrocytes, in contrast, removes all neurite-promoting activity. These results provide evidence for at least two types of neuronal interactions with cells that promote neurite outgrowth. One involves adhesive proteins present in the ECM and ECM receptors on neurons. The second is mediated through detergent-extractable macromolecules present on non-neuronal cell surfaces and different, uncharacterized receptor(s) on neurons. Schwann cells and skeletal myotubes appear to promote neurite outgrowth by both mechanisms

Purification and characterization of mammalian integrins expressed by a rat neuronal cell line (PC12): evidence that they function as alpha/beta heterodimeric receptors for laminin and type IV collagen.

Cells of the rat neuronal line, PC12, adhere well to substrates coated with laminin and type IV collagen, but attach poorly to fibronectin. Adhesion and neurite extension in response to these extracellular matrix proteins are inhibited by Fab fragments of an antiserum (anti-ECMR) that recognizes PC12 cell surface integrin subunits of Mr 120,000, 140,000, and 180,000 (Tomaselli, K. J., C. H. Damsky, and L. F. Reichardt. 1987. J. Cell Biol. 105:2347-2358). Here we extend our study of integrin structure and function in PC12 cells using integrin subunit-specific antibodies prepared against synthetic peptides corresponding to the cytoplasmic domains of the human integrin beta 1 and the fibronectin receptor alpha (alpha FN) subunits. Anti-integrin beta 1 immunoprecipitated a 120-kD beta 1 subunit and two noncovalently associated integrin alpha subunits of 140 and 180 kD from detergent extracts of surface-labeled PC12 cells. Immunodepletion studies using anti-integrin beta 1 demonstrated that these two putative alpha/beta heterodimers are identical to those recognized by the adhesion-perturbing ECMR antiserum. Anti-alpha FN immunoprecipitated fibronectin receptor heterodimers in human and rat fibroblastic cells, but not in PC12 cells. Thus, low levels of expression of the integrin alpha FN subunit can explain the poor attachment of PC12 cells to FN. The PC12 cell integrins were purified using a combination of lectin and ECMR antibody affinity chromatography. The purified integrins: (a) completely neutralize the ability of the anti-ECMR serum to inhibit PC12 cell adhesion to laminin and collagen IV; (b) have hydrodynamic properties that are very similar to those of previously characterized integrin alpha/beta heterodimeric receptors for ECM proteins; and (c) can be incorporated into phosphatidylcholine vesicles that then bind specifically to substrates coated with laminin or collagen IV but not fibronectin. Thus, the ligand-binding specificity of the liposomes containing the purified PC12 integrins closely parallels the substrate-binding preference of intact PC12 cells. These results demonstrate that mammalian integrins purified from a neuronal cell line can, when incorporated into lipid vesicles, function as receptors for laminin and type IV collagen

Identification of a synaptic vesicle-specific membrane protein with a wide distribution in neuronal and neurosecretory tissue.

Two different monoclonal antibodies, characterized initially as binding synaptic terminal regions of rat brain, bind a 65,000-dalton protein, which is exposed on the outer surface of brain synaptic vesicles. Immunocytochemical experiments at the electron microscope level demonstrate that these antibodies bind the vesicles in many different types of nerve terminals. The antibodies have been used successfully to purify synaptic vesicles from crude brain homogenates by immunoprecipitation onto the surface of polyacrylamide beads. The profiles of the structures precipitated by these beads are almost exclusively vesicular, confirming the vesicle-specificity of the antibodies. In SDS gels, the antibodies bind a single protein of 65,000 daltons. The two antibodies are not identical, but compete for binding sites on this protein. Immune competition experiments also demonstrate that the antigenic components on the 65,000-dalton protein are widely distributed in neuronal and neural secretory tissues. Detectable antigen is not found in uninnervated tissue--blood cells and extrajunctional muscle. Low levels are found in nonneural secretory tissues; it is not certain whether this reflects the presence of low amounts of the antigen on all the exocytotic vesicles in these tissues or whether the antigen is found only in neuronal fibers within these tissues. The molecular weight and at least two antigenic determinants of the 65,000-dalton protein are highly conserved throughout vertebrate phylogeny. The two antibodies recognize a 65,000-dalton protein present in shark, amphibia, birds, and mammals. The highly conserved nature of the determinants on this protein and their specific localization on secretory vesicles of many different types suggest that this protein may be essential for the normal function of neuronal secretory vesicles

Interactions of a neuronal cell line (PC12) with laminin, collagen IV, and fibronectin: identification of integrin-related glycoproteins involved in attachment and process outgrowth.

Neuronal responses to extracellular matrix (ECM) constituents are likely to play an important role in nervous system development and regeneration. We have studied the interactions of a neuron-like rat pheochromocytoma cell line, PC12, with ECM protein-coated substrates. Using a quantitative cell attachment assay, PC12 cells were shown to adhere readily to laminin (LN) or collagen IV (Col IV) but poorly to fibronectin (FN). The specificity of attachment to these ECM proteins was demonstrated using ligand-specific antibodies and synthetic peptides. To identify PC12 cell surface proteins that mediate interactions with LN, Col IV, and FN, two different antisera to putative ECM receptors purified from mammalian cells were tested for their effects on PC12 cell adhesion and neuritic process outgrowth. Antibodies to a 140-kD FN receptor heterodimer purified from Chinese hamster ovarian cells (anti-FNR; Brown, P. J., and R. L. Juliano, 1986, J. Cell Biol., 103:1595-1603) inhibited attachment to LN and FN but not to Col IV. Antibodies to an ECM receptor preparation purified from baby hamster kidney fibroblastic cells (anti-ECMR; Knudsen, K. A., P. E. Rao, C. H. Damsky, and C. A. Buck, 1981, Proc. Natl. Acad. Sci. USA., 78:6071-6075) inhibited attachment to LN, FN, and Col IV, but did not prevent attachment to other adhesive substrates. In addition to its effects on adhesion, the anti-ECMR serum inhibited both PC12 cell and sympathetic neuronal process outgrowth on LN substrates. Immunoprecipitation of surface-iodinated or [3H]glucosamine-labeled PC12 cells with either the anti-FNR or anti-ECMR serum identified three prominent cell surface glycoproteins of 120, 140, and 180 kD under nonreducing conditions. The 120-kD glycoprotein, which could be labeled with 32P-orthophosphate and appeared to be noncovalently associated with the 140- and 180-kD proteins, cross reacted with antibodies to the beta-subunit (band 3) of the avian integrin complex, itself a receptor or receptors for the ECM constituents LN, FN, and some collagens

Adhesion of a chicken myeloblast cell line to fibrinogen and vitronectin through a beta 1-class integrin.

The adhesive interactions of circulating blood cells are tightly regulated, receptor-mediated events. To establish a model for studies on regulation of cell adhesion, we have examined the adhesive properties of the HD11 chick myeloblast cell line. Function-perturbing antibodies were used to show that integrins containing the beta 1 subunit mediate HD11 cell attachment to several distinct extracellular matrix proteins, specifically fibronectin, collagen, vitronectin, and fibrinogen. This is the first evidence that an integrin heterodimer in the beta 1 family functions as a receptor for fibrinogen. While the alpha v beta 1 heterodimer has been shown to function as a vitronectin receptor on some cells, this heterodimer could not be detected on HD11 cells. Instead, results suggest that the beta 1 subunit associates with different, unidentified alpha subunit(s) to form receptors for vitronectin and fibrinogen. Results using function-blocking antibodies also demonstrate that on these cells, additional receptors for vitronectin are formed by alpha v beta 3 and alpha v associated with an unidentified 100-kD beta subunit. The adhesive interactions of HD11 cells with these extracellular matrix ligands were shown to be regulated by lipopolysaccharide treatment, making the HD11 cell line attractive for studies of mechanisms regulating cell adhesion. In contrast to primary macrophage which rapidly exhibit enhanced adhesion to laminin and collagen upon activation, activated HD11 cells exhibited reduced adhesion to most extracellular matrix constituents

Molecular cloning and characterization of B-cadherin, a novel chick cadherin.

Calcium-dependent cell-cell adhesion is mediated in large part by a set of homologous integral membrane glycoproteins termed cadherins. In this report, antibodies to conserved domains in previously described cadherins have been used to isolate cDNAs encoding a novel chick cadherin. The deduced primary structure of this novel molecule, assigned the name B-cadherin, contains 726 amino acid residues which include five extracellular domains characteristic of this class of adhesion molecules, a single putative transmembrane spanning region, and a cytoplasmic tail. In each domain, B-cadherin shares extensive homologies with other cadherins, but is more closely related to E-cadherin, P-cadherin, and L-CAM than to N-cadherin. It is expressed in a wide variety of chick tissues at embryonic day 13. In particular, immunohistochemical staining and in situ hybridization localize B-cadherin protein and mRNA to the epithelial lining of the choroid plexus and to cells in specific layers of the optic tectum in chick brain. Levels of the protein and RNA transcript change dramatically as development proceeds in chick brain. These results suggest that B-cadherin has important functions in neurogenesis, in at least some epithelia, and in embryogenesis

Isolation and characterization of a laminin-binding protein from rat and chick muscle.

A major laminin-binding protein (LBP), distinct from previously described LBPs, has been isolated from chick and rat skeletal muscle (Mr 56,000 and 66,000, respectively). The purified LBPs from the two species were shown to be related antigenically and to have similar NH2-terminal amino acid sequences and total amino acid compositions. Protein blots using laminin and laminin fragments provided evidence that this LBP interacts with the major heparin-binding domain, E3, of laminin. Studies on the association of this LBP with muscle membrane fractions and reconstituted lipid vesicles indicate that this protein can interact with lipid bilayers and has properties of a peripheral, not an integral membrane protein. These properties are consistent with its amino acid sequence, determined from cDNAs (Clegg et al., 1988). Examination by light and electron microscopy of the LBP antigen distribution in skeletal muscle indicated that the protein is localized primarily extracellularly, near the extracellular matrix and myotube plasmalemma. While a form of this LBP has been identified in heart muscle, it is present at low or undetectable levels in other tissues examined by immunocytochemistry indicating that it is probably a muscle-specific protein. As this protein is localized extracellularly and can bind to both membranes and laminin, it may mediate myotube interactions with the extracellular matrix

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