DOE OSTI2015
Objective: LeftyA, a powerful regulator of stemness, embryonic differentiation, and reprogramming of cancer cells, counteracts cell proliferation and tumor growth. Key properties of tumor cells include enhanced glycolytic flux, which is highly sensitive to cytosolic pH and thus requires export of H{sup +} and lactate. H{sup +} extrusion is in part accomplished by Na{sup +}/H{sup +} exchangers, such as NHE1. An effect of LeftyA on transport processes has, however, never been reported. The present study thus explored whether LeftyA modifies regulation of cytosolic pH (pHi) in Ishikawa cells, a well differentiated endometrial carcinoma cell model. Methods: NHE1 transcript levels were determined by qRT-PCR, NHE1 protein abundance quantified by Western blotting, pH{sub i} estimated utilizing (2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein [BCECF] fluorescence, Na{sup +}/H{sup +} exchanger activity from Na{sup +} dependent realkalinization after an ammonium pulse, and lactate concentration in the supernatant utilizing an enzymatic assay and subsequent colorimetry. Results: A 2 h treatment with LeftyA (8 ng/ml) significantly decreased NHE1 transcript levels (by 99.6%), NHE1 protein abundance (by 71%), Na{sup +}/H{sup +} exchanger activity (by 55%), pHi (from 7.22 ± 0.02 to 7.05 ± 0.02), and lactate release (by 41%). Conclusions: LeftyA markedly down-regulates NHE1 expression, Na{sup +}/H{sup +} exchanger activity, pHi, and lactate release in Ishikawa cells. Those effects presumably contribute to cellular reprogramming and growth inhibition. - Highlights: • LeftyA, an inhibitor of tumor growth, reduces Na{sup +}/H{sup +}-exchanger activity by 55%. • LeftyA decreases NHE1 transcripts by 99.6% and NHE1 protein by 71%. • LeftyA decreases cytosolic pH from 7.22 ± 0.02 to 7.05 ± 0.02. • Cytosolic acidification by Lefty A decreases glycolysis by 41%. • Cytosolic acidification by Lefty A compromises energy production of tumor cells.
60 APPLIED LIFE SCIENCES↗