Inhibition of ErbB2 causes mitochondrial dysfunction in cardiomyocytes: implications for herceptin-induced cardiomyopathy.

Objectives: We investigated the effects of erbB2 inhibition by anti-erbB2 antibody on cardiomyocyte survival and mitochondrial function.
Background: ErbB2 is an important signal integrator for the epidermal growth factor family of receptor tyrosine kinases. Herceptin, an inhibitory antibody to the erbB2 receptor, is a potent chemotherapeutic but causes cardiac toxicity.
Methods: Primary cultures of neonatal rat ventricular myocytes were exposed to anti-erbB2 antibody (Ab) (7.5 mug/ml) for up to 24 h. Cell viability, mitochondrial function, and apoptosis were measured using multiple complementary techniques.
Results: ErbB2 inhibition was associated with a dramatic increase in expression of the pro-apoptotic Bcl-2 family protein Bcl-xS and decreased levels of anti-apoptotic Bcl-xL. There was a time-dependent increase in mitochondrial translocation and oligomerization of bcl-associated protein (BAX), as indicated by 1,6-bismaleimidohexane crosslinking. The BAX oligomerization was associated with cytochrome c release and caspase activation. These alterations induced mitochondrial dysfunction, a loss of mitochondrial membrane potential (psi) (76.9 +/- 2.4 vs. 51.7 +/- 0.1; p < 0.05; n = 4), a 35% decline in adenosine triphosphate levels (p < 0.05), and a loss of redox capacity (0.72 +/- 0.04 vs. 0.64 +/- 0.02; p< 0.01). Restoration of Bcl-xL levels through transactivating regulatory protein-mediated protein transduction prevented the decline in psi mitochondrial reductase activity and cytosolic adenosine triphosphate.
Conclusions: Anti-erbB2 activates the mitochondrial apoptosis pathway through a previously undescribed modulation of Bcl-xL and -xS, causing impairment of mitochondrial function and integrity and disruption of cellular energetics.