Role of epidermal growth factor receptor (EGFR)-signaling versus cellular acidosis via Na+/H+ exchanger1(NHE1)-inhibition in troglitazone-induced growth arrest of breast cancer-derived cells MCF-7.
OBJECTIVE
We previously showed that troglitazone (TRO) induces a profound cellular acidosis in MCF-7 cells as a result of inhibiting Na(+)/H(+) exchanger (NHE)1-mediated acid extrusion and this was associated with a marked reduction in cellular proliferation. The present study focuses on TRO-activated signaling pathways versus TRO-mediated NHE1-inhibition in reducing DNA synthesis.


METHODS
TRO activation of the signaling pathway involving epidermal growth factor receptor (EGFR)/MAPK/ERK kinase (MEK) 1/2/extracellular signal-regulated kinase (ERK) 1/2 was studied by Western blotting and phospho-specific antibodies. TRO induction of cellular acidosis and inhibition of NHE1 activity were measured using (2, 7)-biscarboxyethyl-5 (6)-carboxyfluorescein (BCECF) assay and NH4(+)/NH(3) pulsing. Cellular proliferation was assessed as DNA synthesis by (3)H-thymidine incorporation.


RESULTS
TRO simultaneously reduces pH(i) and elevates phosphorylated-extracellular signal-regulated kinase (p-ERK). These responses reflected inhibition of acid extrusion and EGFR activation respectively and were sustained over 18h associated with a large decrease in DNA synthesis. Preventing TRO-induced ERK activation did not restore DNA synthesis or cellular pH.


CONCLUSIONS
TRO activates two parallel pathways: I] EGFR/MEK1/2/ERK1/2 and II] NHE1 inhibition/cellular acidosis. Elimination of I] did not prevent the inhibition of DNA synthesis consistent with TRO-induced growth arrest dependent upon II] in tumorigenic non-metastatic breast cancer derived MCF-7 cells.
Friday
Ellen
E
Department of Medicine, Feist-Weiller Cancer Center, Louisiana State University Health Science Center, Shreveport, LA 71103, USA.
Oliver
Robert
R
Welbourne
Tomas
T
Turturro
Francesco
F
D000138:Acidosis / Q000201:enzymology / Q000378:metabolism*; D001943:Breast Neoplasms / Q000201:enzymology / Q000473:pathology*; D027682:Cation Transport Proteins / Q000037:antagonists & inhibitors*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002839:Chromans / Q000494:pharmacology*; D004273:DNA, Neoplasm / Q000096:biosynthesis; D004789:Enzyme Activation / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000494:pharmacology; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism*; D005260:Female; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D008954:Models, Biological; D010750:Phosphoproteins / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors*; D045162:Thiazolidinediones / Q000494:pharmacology*; D015533:Transcriptional Activation / Q000187:drug effects; D000077288:Troglitazone
D027682:Cation Transport Proteins; D002839:Chromans; D004273:DNA, Neoplasm; D010750:Phosphoproteins; C490998:SLC9A1 protein, human; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers; D045162:Thiazolidinediones; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D000077288:Troglitazone