Paclitaxel induces apoptosis via protein kinase A- and p38 mitogen-activated protein-dependent inhibition of the Na+/H+ exchanger (NHE) NHE isoform 1 in human breast cancer cells.
OBJECTIVE
The molecular signal components essential to paclitaxel-dependent apoptosis in breast cancers are potential targets for combined therapy. However, the signal mechanisms underlying paclitaxel action still need to be better defined.


METHODS
In a breast cancer cell line, pharmacological agents and transient transfection with dominant interfering and constitutive active mutants were used to identify the signal transduction module involved in the regulation of paclitaxel-induced apoptosis and to evaluate its potential as a therapeutic target.


RESULTS
In MDA-MB-435 cells, paclitaxel treatment stimulated the activity of both protein kinase A and p38, and inhibited the activity of the Na(+)/H(+) exchanger isoform 1 (NHE1) with similar IC(50) concentrations as for its activation of apoptosis. Activation and inhibition experiments demonstrated that protein kinase A and p38 participate sequentially upstream of the NHE1 in regulating the paclitaxel-induced apoptotic pathway. Importantly, concurrent specific inhibition of the NHE1 with paclitaxel treatment resulted in a synergistic induction of apoptosis and a reduction in the paclitaxel IC(50) for apoptosis. This sensitization of paclitaxel apoptotic action by specific inhibition of NHE1 was verified in breast cancer cell lines with different paclitaxel sensitivity.


CONCLUSIONS
We have, for the first time, identified NHE1 as an essential component of paclitaxel-induced apoptosis in breast cancer cells and, importantly, identified that simultaneous inhibition of the NHE1 results in a synergistic potentiation of low-dose paclitaxel apoptotic action. As specific NHE1 inhibitors have finished Phase II/Phase III clinical trials for myocardial protection, there is the possibility for a rapid biological translation of this novel therapeutic strategy to a clinical setting.
Reshkin
Stephan J
SJ
Department of General and Environmental Physiology, University of Bari, Bari, Italy.
Bellizzi
Antonia
A
Cardone
Rosa Angela
RA
Tommasino
Massimo
M
Casavola
Valeria
V
Paradiso
Angelo
A
D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000473:pathology; D045744:Cell Line, Tumor; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D005260:Female; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology*; D017239:Paclitaxel / Q000494:pharmacology*; D015398:Signal Transduction; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors*; D048051:p38 Mitogen-Activated Protein Kinases
D000972:Antineoplastic Agents, Phytogenic; D017923:Sodium-Hydrogen Exchangers; C069139:growth factor-activatable Na-H exchanger NHE-1; D017868:Cyclic AMP-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D017239:Paclitaxel