Ultraviolet light and serum induce similar delayed responses that lead to activation of a mitogen-responsive promoter.

The transferrin receptor promoter is responsive to growth factors and mitogens. This induction is a delayed response and does not occur until several hours after stimulation of quiescent cells by mitogens. The results described here show that the transferrin receptor promoter is also activated by treatment with ultraviolet (UV) light. Activation of the promoter by UV light is dose dependent and requires the same cis-acting elements that are activated in response to serum and other mitogens. As with serum stimulation, activation of the promoter by UV light is a delayed event and is not initiated until 6 h after treatment. This coincides with the induction of nuclear factors that bind with specificity to the required cis-acting elements. A major GC-box binding factor induced by UV light is also induced by serum and has been shown to be supershifted by antibodies to the Sp1 transcription factor.