Adhesion activity in fibronectin's alternatively spliced domain EDa (EIIIA): complementarity to plasma fibronectin functions

The EDa (EIIIA) domain is one of two alternatively spliced type III homology repeats in fibronectins which differentiate cellular (cFN) from plasma isoforms (pFN). A bacteria-expressed recombinant polypeptide encoding the EDa type III repeat promotes adhesion of some cell types and its activity is synergistic with neighboring repeats III11 and III12. We show in this study that co-coating substrata with the EDa-only polypeptide and a suboptimal concentration of pFN leads to increased attachment and extensive spreading of v-src-transformed 3T3 cells relative to that found on substrata of suboptimal pFN or EDa polypeptide alone. This complementarity of activities requires as little as 1 microgram/ml EDa polypeptide in the adsorbing mixture and displays sequence specificity for only EDa (recombinant polypeptides of neighboring repeats III11 or III12 were without effect). Furthermore, stress fibers and focal contacts are inducible on the EDa:pFN mixture, suggesting that the EDa sequence and its receptor participate in signal transduction. The codistribution of phosphotyrosine proteins, including pp125FAK, along with vinculin and talin into focal contacts supports this hypothesis. Therefore, an alternatively spliced domain EDa which is expressed in various proportions in cells and tissues may have special functions related to adhesion processes by complementing the functions of pFN circulating in blood.

The chloride concentration in the lateral intercellular spaces of MDCK cell monolayers

We measured the Cl concentration of the lateral intercellular spaces (LIS) of MDCK cell monolayers, grown on glass coverslips, by video fluorescence microscopy. Monolayers were perfused at 37 degrees C either with HEPES-buffered solutions containing 137 mM Cl or bicarbonate/CO2-buffered solutions containing 127 mM Cl. A mixture of two fluorescent dyes conjugated to dextrans (MW 10,000) was microinjected into domes and allowed to diffuse into the nearby LIS. The Cl-sensitive dye, ABQ-dextran, was selected because of its responsiveness at high Cl concentrations; a Cl-insensitive dye, Cl-NERF-dextran, was used as a reference. Both dyes were excited at 325 nm, and ratios of the fluorescence intensity at spectrally distinct emission wavelengths were obtained from two intensified CCD cameras, one for ABQ-dextran the other for Cl-NERF-dextran. LIS Cl concentration was calibrated in situ by treating the monolayer with digitonin or ouabain and varying the perfusate Cl between 0 and 137 mM (HEPES buffer) or between 0 and 127 mM (bicarbonate/CO2 buffer). LIS Cl in HEPES-buffered solutions averaged 176 +/- 19 mM (n = 12), calibrated with digitonin, and 170 +/- 9 mM (n = 12), calibrated with ouabain. LIS Cl in bicarbonate/CO2-buffered solutions averaged 174 +/- 10 mM (n = 7) using the ouabain calibration. The Cl concentration of MDCK cell domes, measured with Cl-sensitive microelectrodes and by microspectrofluorimetry, did not differ significantly. Images of the LIS at 3 focal planes, near the tight junction, midway and basal, failed to reveal any gradients in Cl concentration along the LIS. LIS Cl changed rapidly in response to perfusate Cl with characteristic times of 0.8 +/- 0.1 min (n = 21) for Cl decrease and 0.3 +/- 0.04 min (n = 21) for Cl increase. In conclusion, (i) Cl concentration is higher in the LIS than in the bathing medium, (ii) no gradients of Cl along the depth of LIS are detectable, (iii) junctional Cl permeability is high.

Characterization of the mechanism for the chronic activation of diacylglycerol-protein kinase C pathway in diabetes and hypergalactosemia

Similar vascular pathological conditions are observed in diabetic animals and those with diet-induced hypergalactosemia. Both diabetes and hypergalactosemia are believed to cause vascular dysfunction via a common biochemical mechanism. In this study, we have found that both diabetes and hypergalactosemia in the short term (2-4 months) can increase total diacylglycerol (DAG) levels by 52 +/- 9 and 74 +/- 13% in the retina and aorta, respectively, of diabetic dogs, and by 94 +/- 9 and 78 +/- 11% in the retina and aorta, respectively, in dogs with hypergalactosemia as compared with normal control animals (P < 0.01). The elevation of DAG levels was maintained for 5 years in the aortas of diabetic and hypergalactosemic dogs. To characterize the mechanism of the DAG increases, we have determined that total DAG levels were significantly increased in cultured macro- and microvascular cells exposed to elevated glucose (22 mM) and galactose (16.5 mM) levels. These increased levels were not prevented by sorbinil, an aldose reductase inhibitor. One of the sources of the increased DAG levels was probably derived from de novo synthesis from both hexoses as determined by radiolabeling studies. Intracellularly, the DAG elevation activated protein kinase C (PKC) activity with increases of 58 +/- 12% (P < 0.05) and 66 +/- 8% (P < 0.01) in the membrane fraction of cultured aortic smooth muscle cells exposed to elevated glucose and galactose levels, respectively. These findings have clearly demonstrated a possible common biochemical mechanism by which hyperglycemia and hypergalactosemia can chronically activate the DAG-PKC pathway in the vasculature and could be a possible explanation for the development of diabetic vascular complications.

Insulin's effect on protein kinase C and diacylglycerol induced by diabetes and glucose in vascular tissues

We have reported that membranous protein kinase C (PKC) activities and total diacylglycerol (DAG) levels are increased in the heart and aorta of diabetic rats, which cannot be easily reversed by euglycemic control. However, insulin treatment, which achieved euglycemia, can prevent the increase in PKC activities and DAG levels. Chronic exposure to elevated glucose levels (5.5 vs. 22 mM) increased DAG levels in cultured bovine and rat aortic endothelial cells and smooth muscle cells by 31, 140, and 143%, respectively, only after 3 days of incubation. Glyceraldehyde, which can stimulate the de novo synthesis of DAG, significantly increased DAG levels by 7.1 +/- 0.6-fold after only 16 h of incubation. Elevated glucose levels did not affect labeled DAG when all of the vascular cells were incubated with [3H]arachidonate, [3H]glycerol, or [3H]phosphatidylcholine, whereas [3H]palmitate- and [3H]oleic acid-labeled DAG levels were significantly increased, indicating that the glucose-stimulated increase in DAG is derived partially from the de novo synthesis pathway. Immunoblotting studies showed increases only in PKC isoform beta II but not alpha in aortic smooth muscle cells. The phosphorylation level of MARCKS protein, an intracellular substrate of PKC, was also increased, consistent with the PKC activity increase. These findings showed that diabetic and hyperglycemia-induced increases in PKC activity and DAG levels in the heart and aorta are preventable by insulin treatment.

Effect of IGF-I on pig oocyte maturation, fertilization, and early embryonic development in vitro, and on granulosa and cumulus cell biosynthetic activity

Porcine granulosa cells have been shown previously to both secrete and respond to insulin-like growth factor-I (IGF-I), suggesting an autocrine function of this peptide in the follicle. The present work was undertaken to determine possible effects of IGF-I on in vitro maturation, in vitro fertilization, and early embryonic development in culture. Granulosa and cumulus cell proliferation and differentiation based on 3H-thymidine uptake and progesterone production, respectively, were also assessed. The results showed that the cleavage rate of oocytes was markedly stimulated in a dose-dependent manner by the addition of IGF-I to the oocyte maturation medium (P < 0.05). Embryo development beyond the 8-cell stage was improved by IGF-I, reaching a maximum of 22% at 200 ng/ml IGF-I. Treatment with IGF-I after fertilization increased the percentage of total oocyte cleavage (P < 0.05) to approximately 52%, 43%, and 57% at, respectively, 25, 50, and 100 ng/ml IGF-I. 3H-thymidine incorporation by granulosa cells was significantly increased in cultures treated with FSH (3-fold) or IGF-I (6-fold) compared to the control. For the cumulus cells, FSH caused a similar increase (3-fold) in 3H-thymidine incorporation while IGF-I stimulated a 15-fold increase. Progesterone production by the granulosa cells was increased to the same extent by treatment with FSH or IGF-I (4.7 and 5.1-fold, respectively). However, for the cumulus cells, while FSH caused a marked 16-fold increase in progesterone production, IGF-I caused only a marginal increase of 2.5-fold.(ABSTRACT TRUNCATED AT 250 WORDS)

Adhesion activity in fibronectin's alternatively spliced domain EDa (EIIIA) and its neighboring type III repeats: oncogene-dependent regulation

EDa (EIIIA) is one of two alternatively spliced type III repeats in cellular fibronectin (cFN) lacking in plasma fibronectin (pFN). Previous studies using proteolytic fragments of cFN suggested that EDa may harbor adhesion activity for various Balb/c 3T3 cell derivatives. This putative adhesion activity has now been analyzed more directly. EDa and neighboring type III repeats III11 and III12 from human cFN cDNA were subcloned in various permutations and recombinant minigenes expressed in Escherichia coli. Purified recombinant polypeptide corresponding to EDa type III repeat alone is capable of promoting 3T3 cell attachment and limited cytoplasmic spreading, as are neighboring repeats III11 and III12 when tested as single repeats. While EDa alone exhibited 40-60% of the attachment activity of human pFN depending upon cell type, EDa with both neighboring repeats displayed 70-90% of pFN activity; furthermore, cell spreading was more extensive with the three-repeat molecule. Two experimental approaches indicated that cell surface proteoglycans do not participate in these adhesion processes. Finally, the effects of various oncogenes upon transformation of Balb/c 3T3 cells were investigated. Adhesion activity to all three repeats is completely abrogated by two different ras oncogenes, unaffected by the sis oncogene, and elevated by the src oncogene. Furthermore, ras- revertants of ras-transformed cells had reacquired adhesion activity for EDa and its neighboring repeats. Comparison of individual repeats confirmed oncogene-dependent regulation of receptor activity to these sequences--for 3T3 cells, EDa > III11 = III12, but for src-transformed cells III12 >> EDa > III11. These studies reveal a new adhesion-promoting activity in alternatively spliced EDa and in neighboring repeats III11 and III12; this receptor activity is regulated either positively or negatively subsequent to transformation by specific oncogenes.

Phase-sweep method for characterization of cw-laser-induced dielectric gratings

We present a new phase-sweep method for characterizing laser-induced complex dielectric gratings. This characterization requires four parameters: the amplitudes and the spatial phases of both the refractive-index and the absorption components. We apply this phase-sweep method to study a complex polarizability grating in a nominally undoped cubic photorefractive Bi(12)TiO(20) crystal. We determine the polarizability difference afe between alpha(fe) full and an empty photoexcitable deep trap at 633 nm in Bi(12)TiO(20) to be (2.5 - 8.3i +/- 1.0 +/- 3.3i) x 10(-40) Fm(2) in SI units or (2.3 - 7.5i +/- 0.9 +/- 3.0i) x 10(-24) cm(3) in Gaussian units.

Measurement of the complex polarizability of electron traps in Bi(12)SiO(20) by a moving-grating technique

We measure the optical two-beam coupling gain in three nominally undoped cubic n-type Bi(12)SiO(20) crystals as a function of the beam frequency difference Omega and the beam intensity. The crystal geometry is chosen so that the beam coupling through the ordinary photorefractive effect is absent. From the dependence of the gain on Omega the full complex polarizability difference alpha(fe) between a full and an empty deep trap at the wavelength of 515 am is deduced to be (-1.8 - 4.6i +/- 0.7 +/- 1.1i) x 10(-39) F m(2) in SI units or (-1.6 - 4.1i +/- 0.6 +/- 1.0i) x 10(-23) cm(3) in Gaussian units. This suggests that the hole photoexcitation cross section sigma(h) is larger than that for an electron, sigma(e). Our data are consistent with the electron and hole parameters deduced from extensive previous measurements (in one of the crystals) analyzed with the standard electron-hole competition equations. This consistency requires that the average density of full traps be at least 20 times larger than the average density N(A) of empty traps and that sigma(h) be (2.4 +/- 0.8) x 10(-17) cm(2), while N(A) is (1.4 +/- 0.4) x 10(16) cm(-3) and sigma(e) is less than ~6 x 10(-8) cm(2). This is to our knowledge the first determination of these parameters in a sillenite crystal.

Bullous pemphigoid autoantibodies reactive with intracellular basal keratinocyte antigens: studies of subclass distribution and complement activation

Using immunofluorescence (IF) and monoclonal antibodies (MoAbs) to IgG subclasses, terminal complement components, and S-protein/vitronectin, we have extended recent observations concerning reactivity of bullous pemphigoid autoantibodies with intracellular antigens located on the polar tips of basal human keratinocytes (HuK). Using three purified bullous pemphigoid IgG fractions, autoantibody reactivity with these intracellular antigens was present in all four IgG subclasses. When skin sections were used as substrate, an identical IgG subclass distribution of autoantibodies for each bullous pemphigoid IgG fraction was observed, but reactive with the basement membrane zone. All three bullous pemphigoid IgG preparations contained IgG subclass autoantibodies capable of complement fixation. Each IgG fraction resulted in fixation of all of the terminal complement components (C5, C6, C7, C8, and C9) and assembly of the membrane attack complex (MAC) on the polar tips of basal HuK. S-protein/vitronectin was not bound in a similar fashion. Normal IgG fractions yielded consistently negative reactions. Thus, bullous pemphigoid autoantibodies, fixed to polar tips of basal HuK, are found in all four IgG subclasses and will activate complement resulting in generation of MAC.

Complement fixation by pemphigus antibody. V. Assembly of the membrane attack complex on cultured human keratinocytes

Previous studies have shown that pemphigus vulgaris (PV) IgG will fix early complement components (C1q, C4, and C3) to cultured murine epidermal cell surfaces and that PV IgG and complement alter epidermal cell membrane integrity. The present study was undertaken to determine if assembly of terminal complement components (C5, C6, C7, C8, and C9) and expression of C5b-9 neoantigens occur when PV IgG interacts with human keratinocyte (HuK) cell surface antigens in the presence of a source of complement. Monoclonal antibodies specific for C5, C6, C7, C8, C9, and C5b-9 neoantigens were screened for reactivity to the individual complement components in an assembled complex of human C5b-9 on rabbit red blood cell ghosts. Monoclonal antibodies (tissue culture supernatants) that bound to antigenic determinants accessible in the C5b-9 complex were selected for this study using immunofluorescence methods. HuK treated with PV IgG fixed C5, C6, C7, C8, C9, and C5b-9 neoantigens in a characteristic speckled pattern, while normal IgG did not. Heat inactivation or EDTA treatment of the complement source, or substitution of C2-depleted serum abolished C5, C6, C7, C8, C9, and C5b-9 neoantigen staining. PV IgG and complement also resulted in significant cytotoxicity to cell membranes as assessed using an ethidium bromide-fluorescein diacetate assay. These results suggest that PV IgG will activate the membrane attack complex of the complement system on HuK cell surfaces, resulting in cytotoxicity to cell membranes, further implicating complement in the pathogenesis of pemphigus.