¹The Queensland Cancer Fund Research Laboratory, The Queensland Institute of Medical Research, PO Royal Brisbane Hospital, Brisbane, Qld. 4029, Australia

²Section for Radiobiology and Molecular Environmental Research, Röntgenweg 11, 72076 Tübingen, Germany

³The Department of Surgery, University of Queensland, PO Royal Brisbane Hospital, Brisbane, Qld. 4029, Australia

Correspondence to: M F Lavin, The Queensland Cancer Fund Research Laboratory, The Queensland Institute of Medical Research, PO Royal Brisbane Hospital, Brisbane, Qld. 4029, Australia

^aKE Keating and N Gueven contributed equally to the work

There is evidence that ATM plays a wider role in intracellular signalling in addition to DNA damage recognition and cell cycle control. In this report we show that activation of the EGF receptor is defective in ataxia-telangiectasia (A-T) cells and that sustained stimulation of cells with EGF downregulates ATM protein in control cells but not in A-T cells expressing mutant protein. Concomitant with the downregulation of ATM, DNA-binding activity of the transcription factor Sp1 decreased in controls after EGF treatment but increased from a lower basal level in A-T cells to that in untreated control cells. Mutation in two Sp1 consensus sequences in the ATM promoter reduced markedly the capacity of the promoter to support luciferase activity in a reporter assay. Overexpression of anti-sense ATM cDNA in control cells decreased the basal level of Sp1, which in turn was increased by subsequent treatment of cells with EGF, similar to that observed in A-T cells. On the other hand full-length ATM cDNA increased the basal level of Sp1 binding in A-T cells, and in response to EGF Sp1 binding decreased, confirming that this is an ATM-dependent process. Contrary to that observed in control cells there was no radiation-induced change in ATM protein in EGF-treated A-T cells and likewise no alteration in Sp1 binding activity. The results demonstrate that EGF-induced downregulation of ATM (mutant) protein in A-T cells is defective and this appears to be due to less efficient EGFR activation and abnormal Sp1 regulation. Oncogene (2001) 20, 4281-4290.

ataxia-telangiectasia ATM; transcriptional downregulation; EGF; Sp1 transcriptional factor