Interactions of the integrin subunit beta1A with protein kinase B/Akt, p130Cas and paxillin contribute to regulation of radiation survival.
OBJECTIVE
Cell adhesion-mediated radioresistance is a common phenomenon particularly relevant in tumor cells, which might hamper anticancer therapies. To analyze the role of adhesion-mediating beta1-integrins, stably transfected functional beta1A-integrin-expressing GD25beta1A and GD25beta1B cells, which express mutant beta1B-integrins, were compared in terms of radiation survival and beta1-integrin signaling.


METHODS
Cells grown on fibronectin, collagen-III, laminin, vitronectin, anti-beta1-integrin-IgG (beta1-IgG) or poly-l-lysine were irradiated with 0-6Gy in presence or absence of growth factors or inhibitors for phosphatidylinositol-3 kinase (PI3K), i.e. Ly294002 and wortmannin. In addition to colony formation, protein kinase B/Akt (PKB/Akt) kinase activity, focal adhesion kinase (FAK), p130Cas, paxillin and c-Jun N2-terminal kinase (JNK) expression and phosphorylation were analyzed by Western blot technique.


RESULTS
Adhesion of GD25beta1A cells to extracellular matrix proteins or beta1-IgG resulted in growth factor-independent radiation survival. In contrast, serum starved GD25beta1B cells showed a significant (P<0.01) reduction in radiation survival on all substrates. PI3K inhibition moderately or strongly radiosensitized GD25beta1A or GD25beta1B cells, respectively. The pro-survival effects detected in serum starved GD25beta1A cells were due to direct, PI3K-mediated stimulation of PKB/Akt activity by beta1-integrins and induced p130Cas and paxillin phosphorylation. Phosphorylated p130Cas and paxillin subsequently prevented activation of cell death-regulating JNK.


CONCLUSIONS
The data show that beta1-integrin-mediated signaling through the cytoplasmic integrin domains is critical for efficient pro-survival regulation after irradiation. Profound knowledge of the underlying mechanisms of integrin-mediated cellular radioresistance could foster the design of new molecular-targeted anticancer therapies.
Seidler
Julia
J
Bundeswehr Institute of Radiobiology, Munich, Germany.
Durzok
Rita
R
Brakebusch
Cord
C
Cordes
Nils
N
D000818:Animals; D002460:Cell Line; D002470:Cell Survival / Q000528:radiation effects*; D003114:Colony-Forming Units Assay; D050719:Crk-Associated Substrate Protein / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism / Q000528:radiation effects; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000378:metabolism; D006133:Growth Substances / Q000378:metabolism; D019012:Integrin beta1 / Q000378:metabolism* / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D051419:Paxillin / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D011836:Radiation Tolerance; D015398:Signal Transduction
D050719:Crk-Associated Substrate Protein; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006133:Growth Substances; D019012:Integrin beta1; D048031:JNK Mitogen-Activated Protein Kinases; D051419:Paxillin; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt