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 been
shown to relay pro-survival effects via unknown mechanisms. We hypothesized that acute βAR-mediated
EGFR transactivation in the heart promotes differential subcellular activation of ERK1/2 and Akt, promoting
cell 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 phosphorylation
of ERK1/2 (P-ERK1/2) and Akt (P-Akt) in distinct cardiac subcellular fractions. Increased P-ERK1/2 and
P-Akt were observed in cytosolic, plasma membrane and nuclear fractions following ISO stimulation. Whereas
the P-ERK1/2 response was EGFR-sensitive in all fractions, the P-Akt response was EGFR-sensitive only in the
plasma membrane and nucleus, results confirmed in primary rat neonatal cardiomyocytes (RNCM). βARmediated
EGFR-transactivation also decreased apoptosis in serum-depleted RNCM, as measured via TUNEL as
well 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 EGFR
transactivation may regulate apoptotic gene transcription. An Apoptosis PCR Array identified tnfsf10 (TRAIL) to
be altered by ISO in an EGFR-sensitive manner, results confirmed via RT-PCR and ELISA measurement of both
membrane-bound and soluble cardiomyocyte TRAIL levels. βAR-mediated EGFR transactivation induces differential
subcellular activation of ERK1/2 and Akt leading to increased cell survival through themodulation of caspase
3 activity and apoptotic gene expression in cardiomyocytes.