Defective radiation signal transduction in ataxia-telangiectasia cells.
OBJECTIVE
The product of the gene ATM mutated in the human genetic disorder ataxia-telangiectasia (A-T) is predominantly present in the nucleus Compatible with a role in DNA-damage recognition and cell-cycle control. However, ATM is also present outside the nucleus in cytoplasmic and membrane associated vesicles, which may explain the more general signalling defect in A-T. This led us to investigate signalling events initiated by ionizing radiation, remote from the nucleus.


METHODS
A-T and control lymphoblastoid cells were employed to study radiation-induced signalling at the level of protein activation using immunoprecipitation and immunoblotting. Flow cytometry was used to determine mobilization of intracellular Ca2+.


RESULTS
Lymphoblastoid cells from A-T patients were found to be defective in the radiation-induced activation of protein tyrosine kinase p53/p56lyn. In control cells Ca2+ was mobilized in response to gamma-radiation largely from internal stores, and increased significantly over a 20 min period. This mobilization of Ca2+ was either absent or increased very slowly in A-T cells post-irradiation. The same pattern of release was observed after treatment with the radiometric agent, streptonigrin. In addition the phospatidylinositol 3-kinase (PI3-kinase) inhibitor wortmannin suppressed the release of Ca2+.


CONCLUSIONS
These data demonstrate that ionizing radiation activates lyn kinase and leads to the release of Ca2+, and-for the first time-that these steps are ATM-dependent.
Yan
J
J
The Queensland Cancer Fund Research Unit, Queensland Institute of Medical Research, Royal Brisbane Hospital, Herston, Australia.
Khanna
K K
KK
Lavin
M F
MF
D001260:Ataxia Telangiectasia / Q000235:genetics* / Q000503:physiopathology*; D064007:Ataxia Telangiectasia Mutated Proteins; D002118:Calcium / Q000502:physiology; D018797:Cell Cycle Proteins; D004249:DNA Damage / Q000528:radiation effects; D004268:DNA-Binding Proteins; D005434:Flow Cytometry; D006801:Humans; D008214:Lymphocytes / Q000528:radiation effects*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics* / Q000528:radiation effects*; D025521:Tumor Suppressor Proteins
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D025521:Tumor Suppressor Proteins; D011505:Protein-Tyrosine Kinases; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; D002118:Calcium