beta-adrenergic receptor-mediated transactivation of EGFR decreases cardiomyocyte apoptosis through differential subcellular activation of ERK and Akt.pdf

β-Adrenergic receptor (βAR)-mediated transactivation of epidermal growth factor receptor (EGFR) has beenshown to relay pro-survival effects via unknown mechanisms. We hypothesized that acute βAR-mediatedEGFR transactivation in the heart promotes differential subcellular activation of ERK1/2 and Akt, promotingcell survival through modulation of apoptosis. C57BL/6 mice underwent acute i.p. injection with isoproterenol(ISO)±AG 1478 (EGFR antagonist) to assess the impact of βAR-mediated EGFR transactivation on the phosphorylationof ERK1/2 (P-ERK1/2) and Akt (P-Akt) in distinct cardiac subcellular fractions. Increased P-ERK1/2 andP-Akt were observed in cytosolic, plasma membrane and nuclear fractions following ISO stimulation. Whereasthe P-ERK1/2 response was EGFR-sensitive in all fractions, the P-Akt response was EGFR-sensitive only in theplasma membrane and nucleus, results confirmed in primary rat neonatal cardiomyocytes (RNCM). βARmediatedEGFR-transactivation also decreased apoptosis in serum-depleted RNCM, as measured via TUNEL aswell as caspase 3 activity/cleavage, which were sensitive to the inhibition of either ERK1/2 (PD184352) or Akt(LY-294002) signaling. Caspase 3 activity/cleavage was also sensitive to the inhibition of transcription, which,with an increase in nuclear P-ERK1/2 and P-Akt in response to ISO, suggested that βAR-mediated EGFRtransactivation may regulate apoptotic gene transcription. An Apoptosis PCR Array identified tnfsf10 (TRAIL) tobe altered by ISO in an EGFR-sensitive manner, results confirmed via RT-PCR and ELISA measurement of bothmembrane-bound and soluble cardiomyocyte TRAIL levels. βAR-mediated EGFR transactivation induces differentialsubcellular activation of ERK1/2 and Akt leading to increased cell survival through themodulation of caspase3 activity and apoptotic gene expression in cardiomyocytes.