PHYSICAL INTERACTION BETWEEN EPIDERMAL GROWTH-FACTOR RECEPTOR AND DNA-DEPENDENT PROTEIN-KINASE IN MAMMALIAN-CELLS

Binding of extracellular ligands to epidermal growth factor receptors (EGFR) activate signal transduction pathways associated with cell prol iferation, and these events are inhibited by monoclonal antibodies aga inst EGFR, Since efficient DNA repair in actively growing cells may re quire growth factor signaling, it was of interest to explore any linka ge between EGFR-mediated signaling and DNA dependent protein kinase (D NA-PK), an enzyme believed to be involved in repairing double strand b reaks and V(D)J recombination. We report that anti-EGFR monoclonal ant ibodies (mAbs), and not EGFR ligands, trigger a specific early physica l interaction between EGFR and a 350-kDa catalytic subunit of DNA or i ts regulatory heterodimeric complex Ku70/80, in a variety of cell type s, both in vivo and in vitro. Inhibition of EGFR signaling by anti-EGF R mAb was accompanied by a reduction in the levels of the DNA-PK and i ts activity in the nuclear fraction, Confocal imaging revealed that a substantial amount of DNA-PK was co-localized with EGFR in anti-EGFR m Ab-treated cells, Anti-EGFR mAb-induced physical interaction between E GFR and DNA-PK or Ku70/80 was dependent on the presence of EGFR, but n ot on the levels of EGFR, The EGFR associated with DNA-PK or Ku70/80 r etains its intrinsic kinase activity. Our findings demonstrate the exi stence of a novel cellular pathway in mammalian cells that involves ph ysical interactions between EGFR and DNA-PK or Ku70/80 in response to inhibition of EGFR signaling, Our present observations suggest a possi ble role of EGFR signaling in maintenance of the nuclear levels of DNA -PK, and interference in EGFR signaling may possibly result in the imp airment of DNA repair activity in the nuclei in anti EGFR mAb-treated cells.