Plasma membrane transglutaminase and cytosolic transglutaminase form distinct envelope-like structures in transformed human keratinocytes

Cross-linked envelope formation in the transformed human keratinocyte line SV-K14 requires treatment of the cells with a Ca2+ ionophore. Depending on the culture conditions, different extracellular Ca2+ concentrations are necessary to trigger the process which is catalyzed by the enzyme transglutaminase. Confluent cells grown in the presence of serum express only the cytosoluble form of the enzyme and need 5 mM Ca2+ for optimum protein cross-linking, whereas serum-starved cells which additionally contain the plasma membrane associated form of the enzyme require only 1 mM Ca2+. The envelope-like structures thus synthesized are morphologically and biochemically distinct.

Identification and subcellular distribution of cornified envelope precursor proteins in the transformed human keratinocyte line SV-K14

SV-40 transformed human foreskin keratinocytes (line SV-K14) develop under conditions of serum starvation the competence to form cornified envelopes that are characteristic of terminally differentiating epidermal cells. In this cell line, the final assembly of the envelope does not occur spontaneously but must be induced using a calcium ionophore. Five potential precursor proteins with molecular weights of 140K, 90K, 61K, 53K, and 36K, respectively, could be detected in the extracts of envelope competent and noncompetent cells. The 61 kD and the 36 kD precursors were specifically decorated in immunoblots when using an antiserum directed against the purified cornified envelope of SV-K14 cells. The 140 kD protein was identified as involucrin by means of a commercial anti-involucrin antibody. Part of the 61 kD protein was found to be inserted into the plasma membrane after the cells gained envelope competence. The set of precursor proteins used by SV-K14 cells differed markedly from those described in the literature for epidermal cells in vivo and for normal human keratinocytes in vitro. Furthermore, cyanogen bromide cleavage of purified envelopes from transformed and normal keratinocytes revealed a completely different peptide pattern. This indicates that the exact molecular composition of the cornified envelope may not be strictly determined and may vary according to the availability of potential substrate proteins at the very moment when the cross-linking enzyme, the plasma membrane associated transglutaminase, becomes functional.

Localization of bullous pemphigoid antigen (BPA) in isolated human keratinocytes

In early studies, the bullous pemphigoid antigen (BPA) has been localized extracellularly in the lamina lucida in the basement membrane zone. However, trypsin-dissociated basal cells can be tagged with bullous pemphigoid sera (BPS). By immunofluorescence, BPA appears located at the dermal pole of basal cells (BC). This may indicate that when BC are separated from the underlying matrix molecules, chunks of BPA remain attached to them. In the present study, fresh crude initial suspensions (CIS) of epidermal cells were prepared by trypsin-EDTA dissociation. The cells were smeared and air-dried. Polar fluorescent cells (i.e., BC) amounted to 42% +/- 7%. CIS were then passed through a fluorescence-activated cell sorter (FACS). In the fluorescent-positive fractions selected by FACS, 34% +/- 7% only of the BC were present. FACS-negative cell fractions were smeared on glass slides, air-dried, and restained with BPS + fluorescein isothiocyanate; 66% +/- 10% of BC were present in these fractions. This is evidence that trypsin-isolated BC comprise two subpopulations: one with BPA directly accessible, the other not. Viability tests and tissue culture studies indicated that the FACS-positive cell fractions were not viable. BPA was extracted from CIS, FACS-positive, and FACS-negative fractions and immunoblotted against BPS. Identical blots were found. FACS-negative cell fractions were treated with heparitinase, nitrous acid, methanol-chloroform, or EDTA without modifying the number of reacting cells. When BC were treated with Triton X-100 or permeabilized by successive freezings and thawings, the number of positive cells became comparable to those obtained by air-drying smears. Finally, BPA was localized on the intracellular part of hemidesmosomes of BC by immunoelectron microscopy. To see whether BPA was also present extracellularly, suction blisters were raised in minipigs and BPS injected into the blister cavity. BPA was found attached to all cells of the cellular roof but not to the dermal base of the blisters. When pieces of skin kept overnight in cold trypsin were reacted with BPS, BPA was found on both sides (epidermal and dermal) of the split. It is concluded that BPA has two localizations: one extracellular, essentially labile which accumulates at the dermal-epidermal junction; the other essentially stable which remains on the intracellular part of basal cell hemidesmosomes and which can be detected after permeabilization of the cells.

Plasma membrane transglutaminase and cornified envelope competence in cultured human keratinocytes

When confluent cultures of the transformed human keratinocyte line SV-K14 are shifted to serum-free medium the cells achieve, within 4 days, the ability to synthesize a cornified envelope after challenge with the Ca2+ ionophore A23187. During these 4 days the enzyme transglutaminase (EC 2.3.2.13), which catalyses the cross-linking of different envelope precursor proteins, is partially transferred from the cytosolic pool into the plasma membrane. The association of the enzyme with the plasma membrane proves to be an essential step in the envelope formation since a direct correlation between plasma membrane-bound transglutaminase and envelope competence is observed. Retinoids block the insertion of the enzyme and therefore prevent envelope formation.

High-yield purification of plasma membranes from transformed human keratinocytes in culture

The density pertubation technique with cationic silica microbeads was applied to prepare highly purified plasma membranes from cultured human keratinocytes. Trypsinized cells were coated successively with the beads (diameter approximately 50 nm, gravity greater than 2 g/cm3) and polyacrylic acid before they were lysed by osmotic shock and mechanical shear. The plasma membranes remained in the form of large open sheets which could easily be separated from other cell organelles and the cytosol by low-speed centrifugation. The membrane preparation was characterized by scanning and transmission electron microscopy, marker enzyme activities, one-dimensional sodium dodecyl sulfate polyacrylamide electrophoresis, and the specific beta-adrenergic receptor count. A yield of 79 +/- 9% was calculated by comparing the amount of beta-adrenoceptors in the purified membrane preparation with that of a crude cellular particulate fraction. The specific beta-adrenoceptor count of these two preparations was 1.2 +/- 0.02 and 0.2 +/- 0.05 pmol/mg protein, respectively, indicating a 6-fold improved purification with this microbead technique. The purified membranes were essentially free from contamination of other cell organelles.

Interactions between 9-hydroxyellipticine and X rays on mammalian cell survival in vitro

Incubation with 9-hydroxyellipticine (9-OH-E) decreases the survival of X-irradiated CHO cells. The survival decreases in the case of exponentially growing and plateau-phase cells, although cells in exponential phase of growth are more sensitive to the drug alone. Radiosensitivity increases with the drug concentration and whether the cells are incubated with the drug for 1 hr prior to or immediately after irradiation. 9-OH-E inhibits the repair of potentially lethal damage, but recovery from sublethal radiation damage is suppressed only by high drug concentrations. The interaction between 9-OH-E and X-ray damage and repair has been examined. 9-OH-E itself induces DNA single-strand breaks or alkali-labile sites which are repaired by the cells. When drug-incubated cells are X irradiated, a repair-inhibiting action of the drug is observed.

The increased phosphorylation of ribosomal protein S6 in Arbacia punctulata is not a universal event in the activation of sea urchin eggs

Eggs of the sea urchins Arbacia punctulata (Ap), Lytechinus pictus (Lp), and Strongylocentrotus purpuratus (Sp) were labeled to equilibrium with 32PO3-4. Approximately 65-70% of the label in extractable adenine nucleotides comigrates chromatographically with ATP. Autoradiograms of one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) slab gels show that each species possesses a distinct complement of phosphate-exchangeable phosphoproteins. No changes in the phosphoprotein composition are detected in Lp and Sp eggs as a result of fertilization or development for 2.5 hr (with the possible exception of a 43,000 Mr protein in Lp). In Ap, increases in the phosphorylation of bands at Mr's 30,000, 55,000, and 105,000 are seen during the first 10 min postinsemination. The 30,000 Mr band in Ap eggs has previously been identified as ribosomal protein S6 and the hypothesis presented that its increased phosphorylation may be an important step in the activation of protein synthesis at fertilization (D. G. Ballinger and T. Hunt, 1981, Dev. Biol. 87, 277-285). In Lp and Sp eggs S6 (identified by two-dimensional PAGE) is heavily phosphorylated in the unfertilized state and the extent of labeling does not increase after fertilization. If the increased phosphorylation of S6 seen in Ap is indeed related to translational activation, then these results suggest that different sea urchin species may rely on different mechanisms for the activation of protein synthesis.

Repair of gamma-ray induced single-strand breaks in human lymphocytes

Human peripheral blood lymphocytes are one of the most radiosensitive mammalian cells. We tested whether this radiosensitivity was associated with the persistance of unrepaired DNA damage in gamma-irradiated lymphocytes. Repair was determined by measuring the loss and recovery of DNA supercoiling when nucleoids are centrifuged in the presence of increasing amounts of ethidium bromide. Results show a limited repair capacity in resting human lymphocytes after gamma-irradiation.

Protease inhibitors suppress the survival increase mediated by uncouplers in X-irradiated mammalian cells

When mammalian cells are incubated with an uncoupler of oxidative phosphorylation prior to and during X-irradiation, the survival and the mutation frequency are markedly increased. This process requires protein synthesis and is inhibited when the cells are plated in the presence of a protease inhibitor (antipain or leupeptin). These results suggest the existence of an error-prone DNA repair process in X-irradiated mammalian cells.

Enhancement of hyperthermia-induced cytotoxicity upon ATP deprivation

The combined effects of hyperthermia and uncouplers of oxidative phosphorylation (dinitrophenol (DNP) or m-chlorocarbonylcyanide phenyl-hydrazone (CCCP) or 5-thio-d-glucose (5-TG) on mammalian cell survival were studied in vitro. Uncouplers were toxic towards cells treated under aerobic conditions at 41 degrees C, whereas 5-TG potentiated the effect of hyperthermia in the case of hypoxic cells. In aerobic conditions the intracellular ATP concentration was decreased upon action of uncouplers, and similar changes occurred in hypoxic cells treated with 5-TG. The results suggest that the ATP deprivation enhances the cell killing by hyperthermia.

On the immunogenicity of ribosomes and ribosomal proteins isolated from Klebsiella pneumoniae and Streptococcus pneumoniae

The two pathogenic species Streptococcus pneumoniae and Klebsiella pneumoniae were used to analyze the immunogenic role of proteins in ribosomal preparations. The protective activity of ribosomes prepared from either strain and further purified by washing with high-salt concentrations, followed or not by sucrose gradient separation of the particles, was identical to that of crude unwashed ribosomes. Similarly, no substantial alteration of the level of protection was observed after treatment with the antibiotic puromycin. Therefore, the immunizing efficacy of ribosomes does not appear to be due either to the nonribosomal proteins adsorbed at the surface of organelles or to the growing polypeptide chain. It seems rather to be attributable to the structural ribosomal proteins themselves, which were indeed shown to induce alone a significant level of protection.

Influence of dimethylsulfoxide on transcription by bacteriophage T3-induced RNA polymerase

Dimethylsulfoxide (DMSO) up to 25% (v/v) does not cause irreversible alterations of T3 DNA at 42.5 degrees C as assayed by transcription with T3-specific RNA polymerase. The optimal temperature for the formation of polyanion-resistant ternary complexes of the enzyme, T3 DNA, and nascent RNA chains is lowered by 12.5 degrees C in the presence of 20% (v/v) DMSO. The same solvent concentration, however, decreased the temperature optimal for T3 RNA chain elongation by only 2.5 degrees C, indicating that DMSO preferably affects the initiation of T3 RNA synthesis. DMSO accelerates the loss of T3-specific RNA polymerase activity at 24.5 degrees C. Nevertheless, the speed with which the binary complexes between the phage RNA polymerase and DNA are inactivated by heat (42.5 degrees C) is not altered in presence of 20% (v/v) DMSO. The binding of T3-induced RNA polymerase to T3 DNA in polyanion-resistant ternary complexes is influenced by DMSO which makes the enzyme accessible to the inhibitory action of polyvinyl sulfate. Elongation of T3 RNA chains is slowed down by 20% (v/v) DMSO.

Effect of temperature on the transcription by bacteriophage T3-induced RNA polymerase

Bacteriophage T3-induced RNA polymerase is rapidly inactivated at 42 degrees C. Addition of T3 DNA delays this process for 30 s and reduces the rate with which the enzyme activity is lost indicating that a labile binary complex between T3 DNA and polymerase must have been formed. The ternary complex between T3-specific RNA polymerase, T3 DNA, and nascent RNA chains obtained when the enzyme is incubated with T3 DNA, GTP, ATP, and UTP is stable to heat (42 degrees C) and only slowly inactivated by polyvinyl sulfate. The optimal temperature for the formation of polyanionresistant ternary complexes is 30 degrees C while the elongation of T3 RNA chains proceeds fastest at 38 degrees C.