UVB irradiation-induced transcription from the long terminal repeat of intracisternal A particles and UVB-induced secretion of an extracellular factor that induces transcription of the intracisternal A particles in unirradiated cells

Abstract Intracisternal A particles (IAPs) are endogenous defective retroviral-like elements encoded by a family of proviral sequences present as a thousand copies in the mouse genome. In order to analyse the regulation of the long terminal repeat (LTR) directed transcription by UVB, D152 murine cells were transfected with a chimeric construct carrying the LTR of IAP linked to the bacterial chloramphenicol—acetyl—transferase reporter gene and then subjected by UVB irradiation in a dose- and time-dependent manner. Like the human immunodeficiency virus 1 type LTR and in spite of the lack of the nuclear factor κ B consensus sequence, the IAP LTR could be activated by UVB. In addition, the D152 cells produced an extracellular factor are factors in response to UVB irradiation which activated the IAP LTR in unirradiated cells. This factor was detected both when responding cells were cocultured with inducing cells and when conditioned medium from irradiated cultures was added to the cell cultures.