Casein kinase I and II (CK I and CK II) are spontaneously active messenger-independent ubiquitous Ser/Thrspecific protein kinases. Their name is derived from their preference for casein and phosvitin as in vitro substrates. They can be differentiated from each other by a number of features: in contrast to CK I, CK II has a different elution profile on DEAE-cellulose and phosphocellulose, it utilizes GTP as phosphate donor, it is inhibited by heparin and 2,3-bisphosphoglycerate (2,3-BFG) and phosphorylates RRREEETEEE, its specific synthetic substrate (for review see references 4 and 14). CK II is an important enzyme identified in all cell types and species examined and is concerned with signal transduction [6]. Considerable interest in CK II has arisen recently because its activity is stimulated significantly in response to several mitogens [insulin, epidermal growth factor (EGF), insulin-like growth factor-I (IGF-I) etc], it phosphorylates nuclear oncoproteins, and plays a role in the transduction of extracellular signals to the nucleus [7,13].
Psoriasis is an excellent model system for studying non-transformed, cellular proliferation [2]. CK II activity has been shown to be present at high levels in keratinocytes [3]. Because of the considerable interest in the role of growth factors in psoriasis [12], we investigated CK II activity in both clinically affected and unaffected psoriatic epidermis, as well as in normal epidermis.
The group of patients with normal skin comprised five men and five women of mean age 39 years (range, 21-53 years). The psoriatic group comprosed four men and four women of mean age 46 years (range, 29-60 years). Both lesional and non-affected epidermal samples