Phosphatidylinositol 3-kinase mediates activation of ATM by high NaCl and by ionizing radiation: Role in osmoprotective transcriptional regulation

doi:10.1073/pnas.0602911103

Phosphatidylinositol 3-kinase mediates activation of ATM by high NaCl and by ionizing radiation: Role in osmoprotective transcriptional regulation

*National Heart, Lung, and Blood Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20892-1603; and
^‡Department of Pharmacy and Pharmacology, Bath University, Claverton Down, Bath, Avon BA2 7AY, United Kingdom

Contributed by Maurice B. Burg, April 14, 2006

Abstract

High NaCl causes DNA double-strand breaks and activates the transcription factor, TonEBP/OREBP, resulting in increased transcription of several protective genes, including those involved in accumulation of compatible organic osmolytes. Several kinases are known to contribute to signaling activation of TonEBP/OREBP, including ATM, which is a member of the phosphatidylinositol 3-kinase (PI3K)-like kinase family and is activated by DNA double-strand breaks. The purpose of the present studies was to investigate a possible role of PI3K Class IA (PI3K-IA). We found that high NaCl increases PI3K-IA lipid kinase activity. Inhibiting PI3K-IA either by expressing a dominant negative of its regulatory subunit, p85, or by small interfering RNA-mediated knockdown of its catalytic subunit, p110α, reduces high NaCl-induced increases in TonEBP/OREBP transcriptional activity and transactivation, but not nuclear translocation of TonEBP/OREBP, or increases in its abundance. Further, suppression of PI3K-IA inhibits the activation of ATM that is caused by either ionizing radiation or high NaCl. High NaCl-induced increase in TonEBP/OREBP activity is reduced equally by inhibition of ATM or PI3K-IA, and the effects are not additive. The conclusions are as follows: (i) PI3K-IA activity is necessary for both high NaCl- and ionizing radiation-induced activation of ATM and (ii) high NaCl activates PI3K-IA, which, in turn, contributes to full activation of TonEBP/OREBP via ATM.

Footnotes

^†To whom correspondence may be addressed. E-mail: irarrazc{at}nhlbi.nih.gov or maurice_burg{at}nih.gov
Author contributions: C.E.I. performed research; C.E.I., S.G.W., and J.D.F. contributed new reagents/analytic tools; C.E.I., M.B.B., S.G.W., and J.D.F. analyzed data; and C.E.I. and M.B.B. wrote the paper.
Conflict of interest statement: No conflicts declared.
Abbreviations:

Abbreviations:

IR,

ionizing radiation;

PIP3,

phosphatidyl inositol 3-phosphate;

PI3K,

phosphatidylinositol 3-kinase;

PI3K-IA,

PI3K-Class IA;

siRNA,

small interfering RNA.