Ionizing radiation activates Erb-B receptor dependent Akt and p70 S6 kinase signaling in carcinoma cells

Abstract

In this study we have investigated the effects of low dose ionizing radiation (2 Gy) on p70 S6 kinase and Akt signaling with respect to Erb-B receptors in both the A431 squamous and the MDA-MB-231 mammary carcinoma cell lines. Ionizing radiation caused a 2-3-fold increase in p70 S6 kinase activity that was blocked pharmacologically using an EGFR inhibitor (AG1478) alone, or in combination with an Erb-B2 inhibitor (AG825). These results suggested that both EGFR and Erb-B2 receptors could initiate radiation-induced activation of p70 S6K. EGFR dependent Erb-B3 signaling also contributed to p70 S6 kinase activity through recruitment and activation of PI3K, which has been shown to regulate p70 S6 kinase activity. Furthermore, inhibition of the EGFR blocked IR stimulated increases in protein translation, a biologic consequence of p70 S6 kinase activation. We also report that ionizing radiation stimulated Akt activity that was partially independent of PI3K activity, but dependent on Erb-B2 function. Erb-B2 inhibition also correlated with enhanced apoptosis following IR exposure, suggesting an important role for Erb-B2 in cell survival. Together this work demonstrates that the Erb-B receptor tyrosine kinase network stimulates cytoprotective p70 S6 kinase and Akt activity in response to clinically relevant doses of ionizing radiation.

EGFRvIII-mediated radioresistance through a strong cytoprotective response

“…Since we have previously identified MAPK as a downstream effector of the EGFR-mediated cytoprotective response after irradiation, it can be expected that EGFRvIII expression in cells enhances this response relative to EGFRwt. These conclusions may apply to PI3K, which demonstrates higher activity levels in EGFRvIII expressing cells (Moscatello et al, 1998) and acts in concert with MAPK in transmitting EGFR signals after irradiation to enhance antiapoptotic responses (Contessa et al, 2002).…”

“…These data represent the most direct demonstration that radiation-induced activation of EGFR species provides a strong cytoprotective signal with increased radioresistance through enhanced proliferation and repair Reardon et al, 1999;Lammering et al, 2001a). From studies on p185neu (ERBB2), the impact of ERBB receptors on cellular radiosensitivity may not be limited to EGFR and its mutants (O'Rourke et al, 1997(O'Rourke et al, , 1998a, but likely depend upon the entire ERBB expression profile of a given tumor cell (Bowers et al, 2001;Lammering et al, 2001a;Contessa et al, 2002).…”

“…We further investigated the effects of EGFRvIII and EGFRwt expression on the radiation-induced apoptosis in CHO cells 24 h following ionizing radiation exposure (Kennedy et al, 1999;Contessa et al, 2002). By comparison, irradiation of CHO.EGFRvIII cells with a single dose of 4 Gy induced only a minimal 1.1-fold increase (P ¼ NS) in apoptosis relative to unirradiated controls.…”

“…This stimulation of EGFR mediates, through the activation of the MAPK and PI3K pathways, a major cytoprotective response (Schmidt-Ullrich et al, 1996Dent et al, 1999) that confers on cells enhanced radioresistance due to accelerated cell proliferation , an antiapoptotic response (Contessa et al, 2002), and improved repair functions after radiation exposures (Lammering et al, 2001b, c). Both of these responses represent probable underlying mechanisms that modulate the radiosensitivity of human tumor cells in vitro and in vivo upon single and repeated radiation exposures (Schmidt-Ullrich et al, 1996;Lammering et al, 2001a, b).…”

A novel chenodeoxycholic derivative HS-1200 enhances radiation-induced apoptosis in MCF-7 cells

“…Not only did the combination treatment of betulinic acid and irradiation also induce the apoptotic effect in human melanoma cells (20), but proteasome inhibitors and the human immunodeficiency virus protease inhibitor, saquinavir, have been demonstrated to modulate the apoptotic response through the inhibition of NF-κB activation (21)(22)(23). Several publications have provided evidence that signaling cascades originating at the epidermal growth factor receptor (EGFR) activate anti-apoptotic signaling pathways and increase the radiation resistance of tumor cells (24)(25)(26). Furthermore, nitric oxide has been proposed as an intrinsic radiosensitizer in vivo.…”