EGF receptor and PKC kinase activate DNA damage-induced pro-survival and pro-apoptotic signaling via biphasic activation of ERK and MSK1 kinases

DNA damage-mediated activation of extracellular signal-regulated kinase (ERK) can regulate both cell survival and cell death. We show here that ERK activation in this context is biphasic and that early and late activation events are mediated by distinct upstream signals that drive cell survival and apoptosis, respectively. We identified the nuclear kinase mitogen-sensitive kinase 1 (MSK1) as a downstream target of both early and late ERK activation. We also observed that activation of ERKMSK1 up to 4 h after DNA damage depends on epidermal growth factor receptor (EGFR), as EGFR or mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK)/ERK inhibitors or short hairpin RNA-mediated MSK1 depletion enhanced cell death. This prosurvival response was partially mediated through enhanced DNA repair, as EGFR or MEK/ERK inhibitors delayed DNA damage resolution. In contrast, the second phase of ERKMSK1 activation drove apoptosis and required protein kinase C (PKC) but not EGFR. Genetic disruption of PKC reduced ERK activation in an in vivo irradiation model, as did short hairpin RNA-mediated depletion of PKC in vitro. In both models, PKC inhibition preferentially suppressed late activation of ERK. We have shown previously that nuclear localization of PKC is necessary and sufficient for apoptosis. Here we identified a nuclear PKCERKMSK1 signaling module that regulates apoptosis. We also show that expression of nuclear PKC activates ERK and MSK1, that ERK activation is required for MSK1 activation, and that both ERK and MSK1 activation are required for apoptosis. Our findings suggest that location-specific activation by distinct upstream regulators may enable distinct functional outputs from common signaling pathways.