Phosphorylation of epidermal keratins

Area of Science:

• Biochemistry
• Dermatology
• Molecular Biology

Background:

• Phosphorylation is a key post-translational modification regulating protein function.
• Epidermal proteins, particularly keratins, play crucial roles in skin structure and barrier function.
• Altered protein phosphorylation is implicated in various skin diseases.

Purpose of the Study:

• To investigate the pattern of protein phosphorylation in human and rat epidermis.
• To identify the specific phosphorylated proteins and their characteristics.
• To examine alterations in epidermal protein phosphorylation in specific skin conditions, including psoriasis.

Main Methods:

• Exposure of human and rat epidermis to 32P-orthophosphoric acid (in vivo and in vitro).
• Protein extraction and solubility analysis (Tris-HCl buffer, SDS-beta-mercaptoethanol).
• SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and two-dimensional gel electrophoresis.
• Analysis of phosphoprotein patterns in normal skin and various dermatological conditions.

Main Results:

• Identical phosphorylation patterns observed in human and rat epidermis, regardless of isotope delivery method.
• Predominant phosphorylated proteins are SDS-beta-mercaptoethanol soluble, with molecular weights of 45,000-65,000.
• These phosphoproteins co-migrate with keratins, with serine as the phosphate acceptor.
• Phosphorylation patterns remained unchanged in basal cell carcinoma, ichthyosis vulgaris, Kyrle's disease, and Netherton's syndrome.
• A distinct alteration in phosphorylation patterns was observed in psoriasis.
• A 63,000 molecular weight phosphoprotein was present in uninvolved skin but absent in psoriatic plaques.

Conclusions:

• Epidermal protein phosphorylation involves specific keratin-associated proteins, primarily phosphorylated on serine residues.
• The observed alterations in psoriatic skin, specifically the absence of a 63,000 molecular weight phosphoprotein, suggest its potential role in the pathogenesis of psoriasis.