The Acute Effects of Ultraviolet-B Radiation on C-myc and C-Ha Ras Expression in Normal Human Epidermis

It is well known that ultraviolet radiation (UVR) causes DNA damage due to the formation of photoproducts which result in the inhibition of DNA synthesis. It has been reported that DNA damage by physical agents such as UVR and chemical carcinogens induces alteration of certain gene expressions. Recently the transient induction of c-myc and c-Ha ras proto-oncogene expressions has been observed in a human keratinocyte cell line in vitro. The present study was designed to investigate whether the induction of these proto-oncogenes occurs in normal human epidermis after UVR in vivo and to relate these findings to DNA synthesis. C-myc and c-Ha ras transcripts were detected throughout human epidermis before and after UVR. C-myc expression increased significantly 5 h after two times the minimal erythema dose (2 x MED) of UVR, while DNA synthesis of the irradiated skin had recovered from the UVR-induced inhibition. The intensity of c-Ha ras expression remained unchanged at both 5 and 24 h after UVR. These results suggest that the c-myc gene plays an important role in the recovery of keratinocytes from acute damage following UVR.