Studies of Epidermal Protein Metabolism

Remarkable elevation of leukotriene B4 in rat skin after induction of UV photodermatitis

Leukotriene B4 in the skin was remarkably elevated in the rat, but not in the guinea pig or the mouse 48 h after UV-B irradiation. These results were consistent with interspecies difference of PMN infiltration caused by UV-B irradiation. LTB4 in the rat skin was determined by both high-performance liquid chromatography and radioimmunoassay. LTB4 in the rat skin started to increase 24 h after irradiation and became about 65-fold higher in the irradiated site than in the nonirradiated site at the end of 48 h. This elevation was strongly inhibited by topical application of two 5-lipoxygenase inhibitors, AA-861 and piriprost, although the inflammatory reaction or infiltration of polymorphonuclear leukocytes was not much improved.

Characterization of superoxide dismutase from mammalian skin epidermis

Superoxide dismutase provides a protective defense mechanism in cellular compartments against the potential cytotoxicity of superoxide anion generated by ultraviolet radiation. Little information is available about the nature of superoxide dismutase in mammalian skin. We report the isolation and characterization of superoxide dismutase from human, guinea pig, and mouse epidermis. Copper-zinc superoxide dismutase was detected in all the mammalian skin specimens examined. Manganese superoxide dismutase was detected in human and guinea pig epidermis but not in the newborn or adult albino CD1 mouse epidermis. Electrophoresis studies of the extracted and partially purified skin superoxide dismutase on polyacrylamide gel slabs in the presence of sodium dodecylsulfate showed the characteristic molecular weights for subunits of 16,500 for copper-zinc superoxide dismutase, and 23,500 for mangano superoxide dismutase. Studies under nondenaturing conditions revealed significant differences in the mobility of the enzymes, depending on the sources of superoxide dismutase. The mouse epidermal copper-zinc superoxide dismutase was found similar to the bovine liver copper-zinc superoxide dismutase used as an internal standard. The copper-zinc superoxide dismutase of human skin and guinea pig skin showed activity-stained bands characterized by a higher mobility than the same enzyme from mouse or bovine liver. Quantitative data using the beta-NADH oxidation method indicated a 5-10-fold lower content of superoxide dismutase in mammalian epidermis in comparison with other tissues examined during this study, or compared with reported values in the literature.

Stimulation of epidermal protein synthesis in vivo by topical triamcinolone acetonide

The rate of epidermal protein synthesis in vivo was determined in the hairless mouse by a method in which a large dose of [3H]phenylalanine (150 mumol/100 g body wt.) is administered via the tail vein. The epidermal free phenylalanine specific radioactivity rapidly rose to a plateau value which by 10 min approached that of plasma, after which it declined. This dose of phenylalanine did not of itself alter protein synthesis rates, since incorporation of co-injected tracer doses of [3H]lysine and [14C]threonine was unaffected. The fractional rate of protein synthesis obtained for epidermis was 61.6%/day, whereas values for liver and gastrocnemius muscle in the same group of mice were 44%/day and 4.8%/day respectively. When expressed on the basis of RNA content, the value for epidermis (18.6 mg of protein/day per mg of RNA) was approx. 3-fold higher than those for liver and gastrocnemius muscle. Topical administration of 0.1% triamcinolone acetonide increased the epidermal fractional protein synthesis rate by 33% after 1 day and by 69% after 7 days, compared with vehicle-treated controls. These effects were entirely accounted for by the increase in protein synthesis rates per mg of RNA. RNA/protein ratios were unaffected by this treatment.

Mammalian epidermal messenger RNA: identification and characterization of the keratin messengers

A messenger RNA fraction which directs the synthesis of epidermal keratins and other skin proteins has been isolated from adult guinea pigs and newborn rats, utilizing techniques designed to minimize degradation by endogenous nucleases. During the initial extraction procedures an inhibitor of translation was identified. This inhibitor could be removed by sedimentation of the RNA through cesium chloride. Electrophoresis of the resulting RNA on denaturing agarose/urea gels indicated that, in addition to 18S and 28S ribosomal RNAs, several minor species ranging in size from 10S to 28S were present. This heterogeneous RNA stimulated the incorporation of radioactive amino acids into protein in a reticulocyte lysate system which had an absolute dependence on added mRNA. A fraction of the RNA was retained on oligo(dT)-cellulose, indicating the presence of poly(adenylic acid) sequences. This poly(A)-rich material was considerably enriched for mRNA activity. Analysis of the products of synthesis indicated that proteins which migrated as keratins in 1- and 2-dimensional electrophoretic systems were major translation products of both the unfractionated material and poly(A)-containing fractions. The minimum sedimentation coefficient of keratin mRNAs was found to be 18S, a value consistent with the molecular weight of the keratin polypeptides.

Contractile proteins in epidermis. Isolation and properties of guinea-pig epidermal myosin

Proteins of apparent molecular weights between 10 000 and 250 000 could be solubilized from guinea pig epidermis using a Tris/sucrose/ATP buffer. When the ionic concentration of the solubilized extract was made 75 mM with respect to KCl and 2 mM with respect to MgCl2, a protein complex precipitated which on SDS-polyacrylamide gel electrophoresis resolved into bands corresponding in migration to myosin, actin and a number of low molecular weight proteins. Myosin was dissociated from the complex with 0.6 M KI and purified by gel filtration chromatography on an agarose column. The purified epidermal myosin fraction contained a polypeptide of 200 000 molecular weight andtwo low molecular weight polypeptides of 16 500 and 13 000. The amino acid composition of the epidermal myosin heavy chain was similar to that of muscle myosin. At high ionic strength epidermal myosin had high specific (K+ + Ca2+)- and (K+ + EDTA)-ATPase activities and low specific (K+ + Mg2+)-ATPase activity. The pH activity curves of the (K+ + Ca2+)- and (K+ + EDTA)-ATPase were different. ATP was hydrolyzed faster than other nucleoside triphosphates. At low ionic strength, the (K+ + Mg2+)-ATPase activity of epidermal myosin was stimulated two fold by skeletal muscle actin. The myosin formed bipolar filaments in 50 mM KCl in the presence of 5 mM Mg2+.

Biochemical and immunological analysis of a basic protein from newborn rat epidermis

A basic protein, solubilized in buffered salt solutions from keratohyalin granules of newborn rat epidermis, has been purified by ion-exchange chromatography. The relative molecular weight of the protein was determined as 12 800 +/- 200 from its mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The protein is relatively rich in lysine, glycine, alanine, and valine which together comprise about 60% of the total amino acid residues. Using an antibody to this protein, which we have designated fraction 4, we have found that it is specific to rat epidermis and is not present in any other rat tissues or in epidermal extracts from other species. The cells of the four epidermal layers were separated and the amount of fraction 4 in each cell layer was measured by radioimmunoassay. The protein is localized mainly in the upper layers of epidermis. The protein, which binds to DNA, appears in the epidermis just prior to birth, increases during the first week of post-natal life and declines sharply thereafter. Fraction 4 represents about 7% of the total solubilized protein in 7-day-old rat epidermis.

Experimental production of rabbit anti-guinea-pig epidermal cell sera. Comparison to pemphigus antibodies

Anti-epidermal cell sera (AES) were obtained by immunizing rabbits with enzymatically dispersed, viable guinea-pig epidermal cells followed by absorption with guinea-pig red blood cells, spleen and thymus cells, and liver powders. Complement-mediated cytotoxicity and immunofluorescence demonstrated that AES were towards cell surface antigen specific for stratified squamous epithelia of guinea pigs, and cross reacted with the corresponding tissues of humans and monkeys. Immunofluorescence revealed that AES reacted with Hassall's corpuscles and surrounding epithelial cells of the guinea-pig thympus which seemed to share common antigens with the epidermis; AES gave no reaction with other organs. While antigens reactive with pemphigus antibodies (PA) were demonstrated by membrane immunofluorescence to be present on the epidermal cell surface, PA showed no cytotoxicity to guinea-pig and human epidermal cells. Re-treatment of isolated epidermal cells with trypsin showed that antigens ractive with PA were more susceptible to the enzyme than those reactive with AES. These findings suggest that the cell surface antigens binding AES are different from the antigens which bind PA.

Epidermal nucleases: purification and characterization of ribonuclease from mammalian epidermis

The major ribonuclease of adult guinea pig epidermis has been isolated and purfied over 1000-fold by a combination of ammonium sulfate fractionation, affinity and ion-exchange chromatography, and electrophoresis. The purified enzyme is free from phosphodiesterase and phosphatase activities. The ribonuclease is optimally active near neutrality in phosphate buffer, with a Km of 3mu g/ml toward [14-C]RNA from Erhlich ascites tumor cells. (here are no metal requirements for activity. The enzyme catalyzes the endonucleolytic hydrolysis of high molecular weight yeast RNA and it also hydrolyzes polycytidylic and polyuridylic acids, but not polyadenylic, polyguanylic, and polyinosinic acids. The apparent molecular weight of the active enzyme is 28 500.

The detection of carotenoid pigments in human skin

Carotenoid pigments were extracted chemically from both epidermis and dermis obtained from non-carotenemic individuals at autopsy. Absorption maxima characteristic of beta-carotene were found in the extracts of specimens of epidermis following cantharidin application in volunteers made carotenemic by the ingestion of beta-carotene (180 mg/day for 10 weeks). These maxima were absent in the extracts of epidermis obtained from the volunteers before beta-carotene ingestion.