Enzyme of keratinization

A mode of action for butylated hydroxytoluene-mediated photoprotection

Dietarily administered butylated hydroxytoluene (BHT) has previously been shown to inhibit UV radiation induction of carcinogenesis, erythema, and ornithine decarboxylase (ODC) activity. Butylated hydroxytoluene feeding also resulted in significant increases in epidermal absorption and it was suggested that BHT's photoprotective properties might be attributable to a diminution of UV radiation dose reaching respective target sites. To explore this possibility, the contribution of stratum corneum to BHT's photoprotective action was examined. SKH-Hr-1 hairless mice were fed diets containing 0.5% (w/w) BHT for 2 weeks prior to experimentation. Control animals received the unsupplemented ration. Stratum corneum from both groups was isolated and spectral transmission recorded. Transmission, between 280-320 nm, was approximately 65% greater through stratum corneum obtained from control animals compared with that of BHT-treated animals. Further evidence of the biologic significance of this BHT effect upon stratum corneum absorption was obtained when stratum corneum was first removed by tape-stripping, the animals irradiated with 0.45 J/cm2 of UVB, and epidermal ODC activity determined. BHT provided the usual inhibition of ODC activity induction in nonstripped animals, but ODC activity induction in BHT-treated, tape-stripped animals was restored to levels that did not significantly differ from controls. The protective effect exhibited by the stratum corneum could not be attributed to BHT-induced alteration of physical dimension, as neither the thickness of stratum corneum nor the number of stratum corneum layers, as determined from measurement of NaOH-distended frozen sections, differed from controls. Although the mechanism remains obscure, these data support the contention that systemically administered BHT results in diminished levels of UV radiation reaching potential epidermal target sites and delimits a large component of the photoprotective effect to the stratum corneum.

Fucosyl glycopeptide profiles of keratinocytes from various epithelial tissues of the rabbit in relation to differentiation in vivo and in vitro

Keratinocytes have been isolated from rabbit cornea, esophagus, and skin by trypsinization. The freshly isolated cells differed in their morphology, growth characteristics in culture, transglutaminase activity (a marker for differentiation), and the composition of glycoprotein-derived fucopeptides. A clear relationship has been shown between the proportion of low-molecular-weight fucopeptides and the pattern of keratinization, being minimal in cornea and maximal in skin. Comparison with earlier literature suggests that this relationship may be a general feature of epithelial tissue. After several passages in culture, all differences between the three cell types disappeared. The unusual elution pattern of the fucopeptides on gel filtration suggests the possibility of a block at an early stage of glycoprotein synthesis under culture conditions.

Health status of workers with past exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin in the manufacture of 2,4,5-trichlorophenoxyacetic acid: comparison of findings with and without chloracne

Chloracne was found in 52% of 226 workers in a 1979 cross-sectional survey at a plant where 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) had been manufactured from 1948 to 1969. Mean duration of residual chloracne was 26 years, and in 29 subjects, it had been present for 30 years. A significant increased prevalence of abnormal gamma-glutamyl transpeptidase (GGT) and higher mean GGT were found in those with chloracne, compared to those without. Although mean triglyceride values were higher in those with chloracne, the difference was not statistically significant. Neurological examination showed a statistically significant higher prevalence of abnormal sensory findings in those with chloracne. Increased prevalence of angina and reported myocardial infarction in those with chloracne was not significant when age-adjusted. Increased prevalence of reported sexual dysfunction and decreased libido in those with chloracne compared to those without was statistically significant after age adjustment. No differences were found between those with and without chloracne in serum cholesterol, total urinary porphyrins, or in reproductive outcome.

Ornithine decarboxylase may be a multifunctional protein

Ornithine decarboxylase may undergo posttranslational modifications which alter its function. Both transamidation of glutamine residues in the enzyme catalyzed by TGase and phosphorylation of serine and threonine residues catalyzed by a polyamine-stimulated protein kinase have been demonstrated. Data are presented which suggest that these modifications result in translocation of the modified protein to the nucleolus where it regulates the activity of RNA polymerase I to transcribe rDNA, the only active nucleolar genes. Transamidation of specific proteins with primary amines catalyzed by intracellular TGase may be an important posttranslational modification, capable of altering genetic transcription. The rapid half-life of ODC (10-15 min) may be related to rapid posttranslational modification with loss of enzymatic activity rather than to protein degradation.

Transglutaminase may mediate certain physiological effects of endogenous amines and of amine-containing therapeutical agents

Transglutaminase mediation of the effects of certain primary amines and alcohols may be important in receptor coupling to physiological responses. Many of the therapeutic and toxic side effects of drugs also may be related to their covalent linkage of glutamine residues of key regulatory proteins through the catalytic action of transglutaminase. This paper suggests that important therapeutic agents such as digoxin, tetracycline, adriamycin, and actinomycin D may have some effects related to transglutaminase action.