Irradiation of cells with short wavelength ultraviolet light (UVA, B a
nd C) induces the transcription of many genes. The program overlaps wi
th that induced by oxidants and alkylating agents and has both protect
ive and other functions. Genes transcribed in response to UV irradiati
on include genes encoding transcription factors, growth factors, prote
ases and viral proteins. While the transcription of transcription fact
or encoding genes is initiated in minutes after UV irradiation (immedi
ate response genes) and depends exclusively on preformed proteins, the
transcription of protease encoding genes occurs only many hours after
UV irradiation. Transcription factors controlling the activity of imm
ediate response genes are activated by protein kinases belonging to th
e group of proline directed protein kinases immediately after UV irrad
iation. Experimenter evidence suggests that these kinases are activate
d in UV irradiated cells through pathways which are used by growth fac
tors. In fact, the first cellular reaction detectable in UV irradiated
cells is the phosphorylation of several growth factor receptors at ty
rosine residues. This phosphorylation does not depend on UV induced DN
A damage, but is due to an inhibition of the activity of tyrosine phos
phatases. In contrast, for late cellular reactions to UV, an obligator
y role of DNA damage in transcribed regions of the genome can be demon
strated. Thus, UV is absorbed by several target molecules relevant for
cellular signaling, and it appears that numerous signal transduction
pathways are stimulated The combined action of these pathways establis
hes the genetic program that determines the fate of UV irradiated cell
s.