Adhesomes: specific granules containing receptors for laminin, C3bi/fibrinogen, fibronectin, and vitronectin in human polymorphonuclear leukocytes and monocytes.

We have localized several major extracellular matrix protein receptors in the specific granules of human polymorphonuclear (PMN) and monocytic leukocytes using double label immunoelectron microscopy (IEM) with ultrathin frozen sections and colloidal-gold conjugates. Rabbit antibodies to 67-kD human laminin receptor (LNR) were located on the inner surface of the specific granule membrane and within its internal matrix. LNR antigens co-distributed with lactoferrin, a marker of specific granules, but did not co-localize with elastase in azurophilic granules of PMNs. Further, CD11b/CD18 (leukocyte receptor for C3bi, fibrinogen, endothelial cells, and endotoxin), mammalian fibronectin receptor (FNR), and vitronectin receptor (VNR) antigens were also co-localized with LNR in PMN specific granules. A similar type of granule was found in monocytes which stained for LNR, FNR, VNR, CD18, and lysozyme. Activation of PMNs with either PMA, f-met-leu-phe (fMLP), tumor necrosis factor (TNF), or monocytic leukocytes with lipopolysaccharide (LPS), induced fusion of specific granules with the cell membrane and expression of both LNR and CD18 antigens on the outer cell surface. Further, stimulation led to augmented PMN adhesion on LN substrata, and six- to eightfold increases in specific binding of soluble LN that was inhibited by LNR antibody. These results indicate that four types of extracellular matrix receptors are located in leukocyte specific granules, and suggest that up-regulation of these receptors during inflammation may mediate leukocyte adhesion and extravasation. We have thus termed leukocyte specific granules adhesomes.

Scanning electron microscopy of focal contacts on the substratum attachment surface of fibroblasts adherent to fibronectin.

We have examined the cell-to-substratum attachment surface of hamster fibroblasts with scanning EM, and describe the surface ultrastructure of focal contacts and microspikes during cellular attachment and spreading on fibronectin. Nil 8 fibroblasts were seeded onto fibronectin-coated glass coverslips in serum-free medium, fixed, and the fibroblast-fibronectin monolayer was separated from the glass and inverted for scanning electron microscopic (EM) analysis. Focal contact development was detected by interference reflection microscopy and correlated with the immunofluorescence microscopic distribution of fibronectin receptor antigens. The cell undersurface appeared smooth and featureless at 0.5 h when focal contacts were undetectable and fibronectin receptors were distributed diffusely. By 1-2 h, undersurface membrane impressions of focal contacts were detected with scanning EM; their size, shape and distribution matched that of focal contacts seen with interference reflection microscopy (IRM). These contacts had smooth external surfaces and were often arranged in chevron-shaped complexes. However, at 4-6 h, the surface texture of focal contacts became fibrous and the contact periphery was delineated with the orifices of membrane-associated vesicles. Development of this filamentous substructure is correlated with the maximum concentration of fibronectin receptors and fibronectin at focal contacts, suggesting that these molecules are involved in the maturation and stabilization of focal contacts.

Lovastatin, an inhibitor of cholesterol synthesis, induces hydroxymethylglutaryl-coenzyme A reductase directly on membranes of expanded smooth endoplasmic reticulum in rat hepatocytes.

Lovastatin is a potent competitive inhibitor of the rate-limiting enzyme of cholesterol synthesis, 3-hydroxy-3-methylglutaryl-coenzyme A reductase (NADPH) [HMG-CoA reductase; (S)-mevalonate:NADP+ oxidoreductase (CoA-acylating), EC 1.1.1.34]. We determined the subcellular distribution of HMG-CoA reductase at high resolution by means of immunoelectron microscopy on ultrathin frozen liver sections of rats treated with lovastatin and cholestyramine. High concentrations of reductase were located on the outer (cytoplasmic) surfaces of smooth endoplasmic reticulum (SER) membranes induced in hepatocytes by acute drug administration. The enzyme was specifically localized over the whorled SER membranes and was absent from nonwhorled SER, rough endoplasmic reticulum, and peroxisomes. Intense HMG-CoA reductase labeling was only observed in hepatocytes containing high levels of HMG-CoA reductase activity; no staining was detected in untreated livers. These observations show that HMG-CoA reductase is induced as an integral component of the SER membranes that form in rat hepatocytes subsequent to lovastatin treatment and suggest that the formation of SER whorls in rat hepatocytes is due to mechanism-based effects of lovastatin.

Cell surface distribution of fibronectin and vitronectin receptors depends on substrate composition and extracellular matrix accumulation.

We used antibodies against the alpha subunits of the human fibronectin receptor (FNR) and vitronectin receptor (VNR) to localize simultaneously FNR and VNR at major substrate adhesion sites of fibroblasts and melanoma cells with double-label immunofluorescence microscopy. In early (2-6-h) serum-containing cultures, both FNR and VNR coaccumulated in focal contacts detected by interference reflection microscopy. Under higher resolution immunoscanning electron microscopy, FNR and VNR were also observed to be distributed randomly on the dorsal cell surface. As fibronectin-containing extracellular matrix fibers accumulated beneath the cells at 24 h, FNR became concentrated at contacts with these fibers and was no longer detected at focal contacts. VNR was not observed at matrix contacts but remained strikingly localized in focal contacts of the 24-h cells. Since focal contacts represent the sites of strongest cell-to-substrate adhesion, these results suggest that FNR and VNR together play critical roles in the maintenance of stable contacts between the cell and its substrate. In addition, the accumulation of FNR at extracellular matrix contacts implies that this receptor might also function in the process of cellular migration along fibronectin-containing matrix cables. To define the factors governing accumulation of FNR and VNR at focal contacts, fibroblasts in serum-free media were plated on substrates coated with purified ligands. Fibronectin-coated surfaces fostered accumulation of FNR but not VNR at focal contacts. On vitronectin-coated surfaces, or substrata derivatized with a tridecapeptide containing the cell attachment sequence Arg-Gly-Asp, both FNR and VNR became concentrated at focal contacts. These observations suggest that the availability of ligand is critical to the accumulation of FNR and VNR at focal contacts, and that FNR might also recognize substrate-bound vitronectin.

Extracellular matrix-cytoskeletal interactions in rheumatoid arthritis. I. Immunoelectron microscopic analysis of the fibronexus at the adhesive surface of normal porcine type B synoviocytes in vitro.

We studied cell surface interactions between the fibronectin (FN)-containing extracellular matrix and the actin cytoskeleton of normal porcine synoviocytes in vitro, using electron microscopic methods. These type B synovial cells were distinguishable from dermal fibroblasts co-isolated from the same organism, because of their very long cellular processes and their ability to synthesize prostaglandin E2 after stimulation with interleukin-1. With plastic sections, we found end-to-end (tandem) and track-like (lateral) transmembrane associations of extracellular fibers and cortical 5-nm microfilaments localized along the attenuated synoviocyte processes in postconfluent cultures. Very similar FN-actin complexes, termed fibronexus (FNX), have been observed on cultured fibroblasts and on granulation tissue myofibroblasts in vivo. Using double-label immunoelectron microscopy with monospecific antibodies applied to ultrathin frozen sections of synoviocytes cut in situ, we proved that these FNX were indeed composed of associated FN and actin filaments. The striking finding of numerous FNX in cultured type B synoviocytes strongly suggests that the FNX is a major cell surface adhesion site in normal synovium, which may play an important role in pannus formation, connective tissue remodeling, and synoviocyte proliferation in patients with rheumatoid arthritis.

Localization of the fibronexus at the surface of granulation tissue myofibroblasts using double-label immunogold electron microscopy on ultrathin frozen sections.

An intimate transmembrane complex of fibronectin-containing extracellular fibers and actin microfilaments termed the fibronexus has been observed at the adhesive surface of fibroblasts in vitro [19] and along the plasmalemma of myofibroblasts in vivo [22]. Although the observation of coincident actin and fibronectin immunofluorescence patterns in the latter work strongly suggested that the fibronexus is localized at the myofibroblast surface, we only obtained morphological evidence for its existence with electron microscopy. Therefore, in the present study, we have utilized a double-label immunoelectron microscopic technique to localize fibronectin and actin simultaneously in the putative fibronexuses of myofibroblasts within guinea pig granulation tissue, formed 7 to 9 days after skin wounding. This method employed rabbit antifibronectin and mouse anti-actin antibodies, followed by species-specific secondary antibodies conjugated to colloidal gold particles of different sizes. These probes were applied to the surfaces of ultrathin frozen sections mounted on grids. We found that fibronectin and actin were specifically localized on the respective external and internal components of myofibroblast fibronexuses. Our results suggest that specific transmembranous fibronectin-cytoskeletal complexes play an important role in the cohesion of granulation tissue.

Hydroxymethylglutaryl-coenzyme A reductase-containing hepatocytes are distributed periportally in normal and mevinolin-treated rat livers.

Mevinolin is a potent inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA reductase; EC 1.1.1.34), an enzyme that catalyzes the rate-limiting step in cholesterol biosynthesis. We have been studying the hepatic distribution of reductase with immunofluorescence microscopy and liver ultrastructure with electron microscopy in normal and drug-treated rats. In control animals, only about 20% of the hepatocytes were reductase positive. These cells were localized in the periportal lobular zones. The numbers of positive hepatocytes in animals given mevinolin or cholestyramine (or both) were directly proportional to the activities of the HMG-CoA reductase determined biochemically. This induction of HMG-CoA reductase immunofluorescence was centered periportally. Rats given 0.075% mevinolin alone had a homogeneous distribution of reductase staining in their hepatocyte cytoplasm, whereas a combination of 0.25% mevinolin and 3% cholestyramine caused a 150-fold increase in enzyme activity and induced prominent juxtanuclear immunofluorescent globules of HMG-CoA reductase in all hepatocytes. With electron microscopy, these bodies were composed of tightly packed stacks of smooth endoplasmic reticulum cysternae and aggregates of branched smooth endoplasmic reticulum tubules. Our data suggest that a subpopulation of periportal rat hepatocytes may be uniquely specialized for cholesterol synthesis.

In vivo co-distribution of fibronectin and actin fibers in granulation tissue: immunofluorescence and electron microscope studies of the fibronexus at the myofibroblast surface.

The fibronexus ( FNX ), a very close transmembrane association of individual extracellular fibronectin fibers and actin microfilaments, was found previously at the substrate-binding surface of fibroblasts in tissue culture (Singer, 1. 1., 1979, Cell, 16:675-685). To determine whether the fibronexus might be involved in fibroblast adhesion during wound healing in vivo, we looked for co-localization of actin and fibronectin in granulation tissue formed within full-thickness guinea pig skin wounds. At 7-9 d, most of the actin fibers were observed to be coincident with congruent fibronectin fibers using double-label immunofluorescence microscopy. These fibronectin and actin fibers were co-localized at the myofibroblast surface surrounding the nucleus, and along attenuated myofibroblast processes which extended deeply into the extracellular matrix. This conspicuous co-distribution of fibronectin and actin fibers prompted us to look for fibronexuses at the myofibroblast surface with electron microscopy. We observed three kinds of FNXs : (a) tandem associations between the termini of individual extracellular fibronectin fibers and actin microfilament bundles at the tips of elongate myofibroblast processes, (b) plaque-like and, (c) track-like FNXs , in which parallel fibronectin and actin fibers were connected by perpendicular transmembranous fibrils. Goniometric studies on the external and internal components of these cross-linking fibrils showed that their membrane-associated ends are probably co-axial. Using immunoelectron microscopy on ultrathin cryosections, we confirmed that the densely staining external portion of these various FNXs does indeed contain fibronectin. The finding that these FNXs appear to connect collagen fibers to intracellular bundles of actin microfilaments is particularly significant. Our studies strongly suggest that the fibronexus is an important in vivo cell surface adhesion site functioning in wound repair, and perhaps within fibronectin-rich tissues during embryogenesis, tumor growth, and inflammation.

Nicarbazin complex yields dinitrocarbanilide as ultrafine crystals with improved anticoccidial activity.

Nicarbazin, a drug used to control the protozoal disease coccidiosis in poultry, is a complex of the highly insoluble drug 4,4'-dinitrocarbanilide with 2-hydroxy-4,6-dimethylpyrimidine. The structures of this and other 4,4'-dinitrocarbanilide complexes have not been determined, but an analogous 2:1 complex of 4,4'-dinitrodiphenylamine with 1,4-diacetylpiperazine has been prepared in which the only possible bonds are hydrogen bonds between the amide carbonyls and amino hydrogens. Scanning electron microscopy revealed that micron-size crystals of nicarbazin disintegrate in water to form much smaller dinitrocarbanilide crystals. Similar complex dissolution in the gut of poultry may account for the greater effectiveness of dinitrocarbanilide when administered as complexed rather than uncomplexed drug. Particle size problems associated with other highly insoluble drugs and pesticides may be resolved by the use of nicarbazin-like complexes.