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Differentiating EGFR activation vs NHE1 inhibition in TRO induced growth arrest of breast cancer cell line MCF‐7
Author(s) -
Friday Ellen,
Oliver Robert,
Welbourne Tomas,
Turturro Francesco
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.1214.3
Subject(s) - mapk/erk pathway , chemistry , apoptosis , cell growth , intracellular , intracellular ph , troglitazone , medicine , acidosis , endocrinology , citric acid , cell culture , biochemistry , biology , receptor , signal transduction , peroxisome , genetics
Troglitazone acts at both the EGFR and NHE1 to induce ERK activation and a cellular acidosis. Because the former site may promote cell growth whereas NHE1 inhibition is associated with growth arrest, we determined the relative sensitivity of these two sites to TRO over a concentration range from 1–20uM. MCF‐7 cells were incubated over 12min in a weakly buffered KH media and ERK activation (ratio p‐ERK/total ERK) and NHE1 activity ( NH 4 + / acid pulse) assayed. At 20uM TRO, ERK activation increased 9.2 fold (p<0.001) vs. time control and NHE1 activity decreased (p<0.01) to 39% of control (0.035±0.006 vs. 0.090±0.003). Intracellular pH at the end of 12 min decreased (p<0.001) from 7.32±0.04 to 6.73±0.05 associated with a large retention of acid ( =20mmol/pHi) within the cells (114±16 vs. 1±14nmole H+/12min, p<0.01); lactate released over the 12min was not increased (66±4 vs. 61±7nmole and accounted for 20% and 48% of the total acid produced respectively) suggesting acid produced from some source other than glycolysis. At 1uM TRO, ERK activation increased 2.4fold (p<0.05) without a decreased NHE1 activity but with a fall (p<0.05) in pHi (7.08±0.06 vs. 7.34±0.05). Acid production increased (223±22 vs. 151±14nmole, p<0.05) over control without an increase in lactate production; similar results were obtained at 5uM TRO. Inhibiting MEKK with PD98059+UO126 prevented both ERK activation and the increased acid production with 20uM TRO and reduced the rate of acidification but not the final pHi or NHE1 inhibition. These results are consonant with a close relationship between EGFR and NHE1 and that the former may support growth via activation of ERK and a subsequent acidogenic metabolic pathway which responds to 20fold lower concentrations of TRO than NHE1 inhibition.