Roles of cytokines and cell cycle regulating substances in proliferation of cholesteatoma epithelium

Objectives: It can be surmised that the cell cycle must be involved in cell proliferation of the epithelium of middle ear cholesteatoma. Thus a compar ative study was conducted of the levels of expression of cyclin-dependent k inase 2 (cdk2) send cyclin-dependent kinase 4 (cdk4)-substances known to be involved in the cell cycle-in cholesteatoma epithelium and the normal epit helium of the bony region of the external ear canal. In addition, it has be en reported that the expression of cytokines in the epithelium is accelerat ed in response to subepithelial inflammation. This suggests that an interac tion between the epithelium and subepithelium, which is subject to paracrin e regulation, is deeply involved in epithelial proliferation. Accordingly, attention was focused on interleukin-1 alpha (IL-1 alpha) and keratinocyte growth factor (KGF), cytokines which are found in the subepithelium, and ex periments were conducted to elucidate their effects on the expression of th e substances known to be involved in the cell cycle. Methods: The expressio ns of cdk2 and cdk4 in the cholesteatoma epithelium and external ear canal epithelium were investigated by an immunohistochemical technique. In additi on, cultured human keratinocytes were grown in medium containing IL-1 alpha or KGF at concentrations of 0, 20, and 100 ng/mL, and the differences in t he expression of cdk2 and cdk4 were investigated and compared by Western bl ot analysis. Results: In the cholesteatoma epithelium specimens, cdk2 and c dk4 were observed to be expressed in the basal and parabasal layers and in the upper layer (prickle layer and granular layer). Their expression tended to be increased compared with their expression in the normal external ear canal epithelium, and this tendency was marked in sub-epithelial sites show ing severe inflammation, In addition, exposure of cultured human keratinocy tes to IL-1 alpha or KGF resulted in accelerated expression of both cdk2 an d cdk4, and this was especially striking in the ease of addition of KGF. Co nclusion: It can be surmised that, in cholesteatoma, accelerated expression of IL-1 alpha and KGF by inflammatory cells at sub-epithelial sites of inf lammation leads to upregulation of cdk2 and cdk4 in epithelial cells and to cell proliferation. It was concluded that this is at least one sequence of events involved in the mechanism causing epithelial proliferation in chole steatoma.