The aim of this study was to determine whether gamma-rays affect differentiation in mouse epidermal cells. After a pre-treatment with the PKC inhibitor staurosporin (STS) or 1-(5-isoquinolinesulfomyl)-2-methylpiperazine (H7), gamma-rays were irradiated with or without an elevation of 0.12 mM Ca2+ and expressions of differentiation markers and each PKC isozyme were examined in normal primary and v-rasHa transformed mouse keratinocytes. Gamma-rays induced the expressions of differentiation markers of keratin 1 and 10 (K1 and 10), filaggrin, loricrin and SPR-1 in normal keratinocytes when the Ca2+ concentration was increased, and these phenomena were augmented in H7 pretreated cells. Similar results were obtained in STS pretreated cells; in this case, gamma-rays enhanced the expressions of the differentiation markers even without an elevated Ca2+ concentration. In v-rasHa transformed cells, gamma-rays induced the expression of differentiation markers not only at 0.05 mM Ca2+, but in 0.12 mM Ca(2+)-shifted cells, and in H7 pretreated cells, these phenomena were augmented. The translocation of PKC alpha to the particulate fraction was seen in H7 pretreated normal keratinocytes. Radiation also induced PKC alpha expression in STS pretreated cells, independent of Ca(2+)-shift, as well as altered expressions of PKC delta and -eta, while expressions of PKC alpha, -delta, -epsilon, and -eta were enhanced in v-rasHa transformed cells. In conclusion, gamma-rays augmented the expressions of both spinous and granular differentiation markers in normal and v-rasHa transformed keratinocytes and this effect was augmented when PKC inhibitors were used, which may be mediated by the cellular redistribution of PKC isozymes.