Induction of Transcription from the Long Terminal Repeat of the Intracysternal Particles Type A (IAP) by X-irradiation

Abstract

Intracisternal A particles (IAPs) are retrovirus-like entities that are present in many embryonic and transformed cells of Mus musculus. They present long terminal repeats (LTRs) which control the promotion and regulation of their transcription. Using a construction expressing a reporter gene under the control of the entire long terminal repeat (LTR) of IAP in transfected murine fibroblast BALB/c 3T3 cells clone D152, we were able to show that the IAP-LTR is activated by X-irradiation in a time-dependent manner. The relative CAT activity increased with increasing X-irradiation doses, reaching a maximum at 75–150 cGy, followed by a drop in activation. In addition, X-induced D152 mouse cells produced extracellular factor(s), in response to X-irradiation, which activated the IAP-LTR in non-irradiated cells. This factor(s) was detected both when transfected cells were cocultured with inducing cells and when conditioned medium from irradiated cultures was added to the cell cultures. The use of suramin, a strong polyanonic molecule which has been reported to trap growth factors, induces a high reduction of the indirect activation.