CYCLIC 3'',5'' ADENOSINE MONOPHOSPHATE-DEPENDENT PROTEIN KINASE OF SKIN

Summary.— The presence of cAMP-dependent protein kinase activity has been confirmed in skin homogenates. Half-maximal stimulation was observed at about 5× 10⁻⁸ mol/1 cAMP, which is very similar to figures reported for protein kinase preparations from other tissues. The apparent K_m for ATP, however, was lower than values previously reported, and was unaltered by the presence of cAMP.     

Studies on the plasma membrane of normal and psoriatic keratinocytes

Cyclic AMP levels have been determined for the first time in isolated keratinocytes. Values were more reproducible than those reported using epidermal slices. Evidence is presented to show that damage to hormone receptors is minimal. Other observations include the following: (1) Keratinocytes from psoriatic lesions showed reduced 'resting' levels of cyclic AMP as well as a diminished response to adrenaline. (2) Cyclic AMP levels were maximal in the basal cells, falling dramatically in fully differentiated keratinocytes. (3) The topical application of a corticosteroid (fluocinolone acetonide) did not modulate the response of adenyl cyclase to hormonal stimulation.     

Lysosomal hydrolases of the epidermis

The activity of twelve acid hydrolases has been measured in serial horizontal sections of cow snout epidermis. The majority of these enzymes showed a clear peak in the basal and lower spinous cell layers; acid phosphatase, however, was found mainly in the keratinizing zone. These findings suggest that two discrete populations of lysosomes may occur in epidermis. Those present in the lower layers possess a typical pattern of hydrolase activity and probably correspond to the 'orthodox' lysosomes observed by electron microscopy techniques, whereas those found in the keratinizing zone possess an unusual hydrolase profile and may correspond to the bodies identified morphologically as keratinosomes (Odland bodies, membrane-coating granules).     

Studies on the plasma membrane of normal and psoriatic keratinocytes. 5. Lectin binding

The glycocalyx of epidermal keratinocytes from psoriatic patients has been investigated by means of lectins. Striking changes were found in the levels of glucose and/or mannose (concanavalin A) and of N-acetylglucosamine and/or sialic acid (wheat germ agglutinin) on the surface of cells from the psoriatic lesion. Smaller but significant changes were seen in the clinically uninvolved epidermis of the patient. A marked increase in the affinity of the cell surface for Ulex europus agglutinin (fucose-specific) confirms our previous reports of structural alterations in fucose-containing oligosaccharides in psoriasis.     

Reduced activation of epidermal phosphorylase in the lesions of psoriasis

The percentage activation of the enzyme phosphorylase in extracts prepared from the epidermis of psoriatic lesions was found to be significantly lower than normal. This observation lends strong support to the concept of a reduced level of cyclic AMP in the lesion of this disease.     

Lectin binding studies on suspensions of isolated epidermal keratinocytes

The sugar composition of the surface of isolated human keratinocytes has been investigated using lectins. A method is described in which the FITC-labelled lectin is displaced with competing sugar prior to measurement. This avoids errors due to aspecific binding and utilizes the minimum biological sample. Evidence is presented which indicates that little cell surface glycoconjugate is lost during the preparation of the keratinocyte suspension from human epidermal slices using the technique described here. Values for keratinocytes are similar to those reported for fibroblast lines, being much higher than those found using erythrocytes or lymphocytes.     

4. OVERALL PROFILE IN COMPARISON WITH DERMIS AND OTHERTISSUES Lysosomal hydrolases of the epidermis

The activities of fifteen acid hydrolases have been measured in seven tissues of the guinea-pig; fourteen of these were also assayed in the epidermis of four other mammalian species. The most striking finding was that the proportion of acid phosphatase was consistently much higher in epidermis than in the other tissues investigated.     

Lysosomal hydrolases of the epidermis

Seven distinct glycosidases (EC 3·2) have been characterized in guinea-pig epidermis. Their properties indicate them to be of lysosomal origin. The ‘profile’ of the epidermal glycosidases is significantly different from that reported for whole skin, the activities of β-galactosidase and β-acetylglucosaminidase being very high and those of the remaining enzymes relatively low in epidermis.