Intracellular pH regulation in hep G2 cells: Effects of epidermal growth factor, transforming growth factor-α, and insulinlike growth factor-II on Na+H+ exchange activity

doi:10.1016/0270-9139(95)90584-7

Hepatology

Volume 22, Issue 2, August 1995, Pages 588-597

https://doi.org/10.1016/0270-9139(95)90584-7 Get rights and content

Abstract

Intracellular pH (pHi) plays an important role in the metabolic activation of quiescent cells after a proliferative stimulus, and $Na^{+} H^{+}$ exchange activity is required for growth in some extrahepatic tumors. To investigate intracellular acid/base homeostasis in hepatoma cells and the effects of putative liver growth factors on $Na^{+} H^{+}$ exchange activity, we have studied intracellular pH (pHi) regulation in Hep G2 cells, a well-differentiated hepatoma cell line, both in resting conditions and after administration of epidermal growth factor (EGF), transforming growth factor-α (TGFα), and insulinlike growth factor-II (IGF-II). The effects of fetal calf serum, TGFα, and amiloride on ³H-Thymidine incorporation were also studied. Amiloride (1 mmol/L) and external Na⁺ removal decreased baseline pHi in both HEPES and KRB. In HEPES, cells recovered from an acid load (20 mmol/L NH₄C1) by an amiloride inhibitable $Na^{+} H^{+}$ exchange. In KRB, an additional, DIDS-inhibitable, Na⁺ and HCO₃-dependent, but Cl^--independent acid extruder (Na:HCO₃ cotransport) was activated. No evidence was found for a Cl/HCO₃ exchange acting as acid loader. Administration of EGF and TGFα, but not of IGF-II, induced a dosedependent, amiloride-inhibitable increase in baseline pHi, together with an increase in $Na^{+} H^{+}$ exchange activity, shifting to the right the JH/pHi curve. Finally, ³Hthymidine incorporation in Hep G2 cells, in the presence of FCS or TGFα, was strongly inhibited by amiloride. In conclusion, in Hep G2 cells, pHi is mainly regulated by $Na^{+} H^{+}$ exchange, which activity can be stimulated by EGF and TGFα, but not by IGF-II. Administration of TGFα stimulates DNA synthesis, an effect that is blocked by amiloride, an inhibitor of $Na^{+} H^{+}$ exchanger. These data suggest that $Na^{+} H^{+}$ exchange activation may play a critical role in the growth of some hepatic tumors.

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Indeed, increased NHE activity has been associated with hepatocyte proliferation, regeneration and growth [53]. NHE1 expression and activity are increased in HCC, with NHE1 inhibition limiting HCC tumor growth [54,55]. Inhibition of NHE activity has also been reported to attenuate liver fibrosis [56], indicating a role for augmented Na+/H+ exchange in HSC activation and proliferation [57].
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^☆: This work has been sponsored by grant 94.02908.CTO4 and “Progetto Nazionale Invecchiamento” from Consiglio Nazionale delle Ricerche (Italy) and by “Centro per lo studio dell'invecchiamento,” University of Padova.

^☆☆: This work has been presented at the AASLD meeting '92 and published as an abstract in HEPATOLOGY 1992; 16: 138A.

¹: Dr. Zsembery was a recipient of an International Fellowship from the University of Padova.

View full text

Intracellular pH regulation in hep G2 cells: Effects of epidermal growth factor, transforming growth factor-α, and insulinlike growth factor-II on Na+H+ exchange activity☆,☆☆

Abstract

Biochim Biophys Acta

J Biol Chem

FEBS Lett

J Biol Chem

Cell

J Biol Chem

Cell

Gastroenterology

Gene

Hepatocellular carcinoma: recent progress

Hepatology

Cirrhosis of the liver: a regenerative process

Dig Dis Sci

Cell regeneration in the pathobiology of liver carcinomas

Gastroenterology

ras oncogenes in human cancer: a review

Cancer Res

Early signals in the mitogenic response

Science

Control of intracellular pH

Hep G2 cells as a resource for metabolic studies: lipoprotein, cholesterol, and bile acids

FASEB J

Protooncogenes and growth factors associated with normal and abnormal liver growth

Dig Dis Sci

Biology of disease: regulation of liver growth: protooncogenes and transforming growth factors

Lab Invest

Growth of normal human hepatocytes in primary culture: effect of hormones and growth factors on DNA synthesis

Hepatology

Intracellular pHi regulation in isolated rat bile duct epithelial cells

J Clin Invest

Effect of ursodeoxycholic acid on intracellular pH in a bile duct epithelium-like cell line

Hepatology

pH regulation in single glomerular mesangial cells. I. Acid extrusion in absence and presence of HCO3

Am J Physiol

pH regulation in single glomerular mesangial cells. II. Na-dependent and -independent Cl/HCO3 exchangers

Am J Physiol

Cl/HCO3 exchanger in isolated rat hepatocytes: role in regulation of intracellular pH

Am J Physiol

Enhancing effect of low frequency pulsed electromagnetic fields (PEMSs) on lectine induced human linfocite proliferation

J Bioelec

Bile canaliculus formation in cultured Hep G2 cells

Lab Invest

Bicarbonate-dependent and -independent intracellular regulatory mechanisms in rat hepatocytes: evidence of Na+-HCO3 cotransport

J Clin Invest

Increased expression of insulin-like growth factor-II/mannose-6-phosphate receptor in regenerating rat liver

Endocrinology

Synthesis of messenger RNAs for transforming growth factors α and β and the epidermal growth factor receptor by human tumors

Cancer Res

Intracellular pH regulation in hep G2 cells: Effects of epidermal growth factor, transforming growth factor-α, and insulinlike growth factor-II on $Na^{+} H^{+}$ exchange activity☆,☆☆

pH regulation in single glomerular mesangial cells. I. Acid extrusion in absence and presence of HCO₃

pH regulation in single glomerular mesangial cells. II. Na-dependent and -independent Cl/HCO₃ exchangers

Cl/HCO₃ exchanger in isolated rat hepatocytes: role in regulation of intracellular pH

Bicarbonate-dependent and -independent intracellular regulatory mechanisms in rat hepatocytes: evidence of Na⁺-HCO₃ cotransport