Phosphorylation of epidermal keratins

When human and rat epidermis are exposed to 32P-orthophosphoric acid, labeled phosphate is incorporated into several proteins. The pattern of phosphorylation is identical whether the isotope is delivered in vivo or in vitro. The predominant phosphorylated proteins are insoluble in Tris-HCl buffer but soluble in SDS-beta-mercaptoethanol. They migrate in SDS-polyacrylamide gels with apparent molecular weights between 45,000 and 65,000. When analyzed by two-dimensional gel electrophoresis, the labeled phosphoproteins co-migrate with keratins isolated from human callus. Serine is the phosphate acceptor in these proteins. The pattern of phosphorylation of these SDS-beta-mercaptoethanol soluble epidermal proteins is not changed in basal cell carcinoma, icthyosis vulgaris, Kyrle's disease or Netherton's syndrome. The pattern is altered in psoriasis. Others have demonstrated that a 63,000 molecular weight protein is absent from active psoriatic lesions. We have found that a 63,000 molecular weight phosphoprotein is present in uninvolved skin but absent in the psoriatic plaques.