Transcriptional downregulation of ATM by EGF is defective in ataxia-telangiectasia cells expressing mutant protein.
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.
Keating
K E
KE
The Queensland Cancer Fund Research Laboratory, The Queensland Institute of Medical Research, PO Royal Brisbane Hospital, Brisbane, Qld. 4029, Australia.
Gueven
N
N
Watters
D
D
Rodemann
H P
HP
Lavin
M F
MF
D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins; D002460:Cell Line; D002478:Cells, Cultured; D016373:DNA, Antisense / Q000235:genetics; D004268:DNA-Binding Proteins; D015536:Down-Regulation; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D066246:ErbB Receptors / Q000378:metabolism; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D006801:Humans; D009154:Mutation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism; D011839:Radiation, Ionizing; D016329:Sp1 Transcription Factor / Q000378:metabolism; D025521:Tumor Suppressor Proteins
D018797:Cell Cycle Proteins; D016373:DNA, Antisense; D004268:DNA-Binding Proteins; D016329:Sp1 Transcription Factor; D025521:Tumor Suppressor Proteins; D004815:Epidermal Growth Factor; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D066246:ErbB Receptors; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases