Phosphoinositide 3-Kinase Is Involved in the Tumor-specific Activation of Human Breast Cancer Cell Na+/H+Exchange, Motility, and Invasion Induced by Serum Deprivation

doi:10.1074/jbc.275.8.5361

Phosphoinositide 3-Kinase Is Involved in the Tumor-specific Activation of Human Breast Cancer Cell Na⁺/H⁺Exchange, Motility, and Invasion Induced by Serum Deprivation*

From the ^‡Department of General and Environmental Physiology, University of Bari, the ^¶Laboratory of Experimental Oncology, Oncology Institute of Bari, 70126 Bari, Italy, and the ^‖Angewandte Tumorvirologie, Deutsches Krebsforschungszentrum, INF 242, Heidelberg, Germany

Abstract

Whereas the tumor acidic extracellular pH plays a crucial role in the invasive process, the mechanism(s) behind this acidification, especially in low nutrient conditions, are unclear. The regulation of the Na⁺/H⁺ exchanger (NHE) and invasion by serum deprivation were studied in a series of breast epithelial cell lines representing progression from non-tumor to highly metastatic cells. Whereas serum deprivation reduced lactate production in all three cells lines, it inhibited NHE activity in the non-tumor cells and stimulated it in the tumor cells with a larger stimulation in the metastatic cells. The stimulation of NHE in the tumor cell lines was the result of an increased affinity of the internal H⁺regulatory site of the NHE without changes in sodium kinetics or expression. Serum deprivation conferred increased cell motility and invasive ability that were abrogated by specific inhibition of the NHE. Inhibition of phosphoinositide 3-kinase by overexpression of a dominant-negative mutant or wortmannin incubation inhibited NHE activity and invasion in serum replete conditions while potentiating the serum deprivation-dependent activation of the NHE and invasion. These results indicate that the up-regulation of the NHE by a phosphoinositide 3-kinase-dependent mechanism plays an essential role in increased tumor cell invasion induced by serum deprivation.

Footnotes

↵* This work was supported by Consiglio Nazionale delle Ricerche Grant 97.00592.CT11.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵§ To whom correspondence should be addressed: Dept. of General and Environmental Physiology, University of Bari, Via Amendola 165/A, 70126 Bari, Italy. Tel.: 0039 80 544-3332; Fax: 0039 80 544-3388; E-mail: reshkin@biologia.uniba.it.
Abbreviations:

pH_i

intracellular pH

NHE

Na⁺/H⁺ exchanger

PI3K

phosphoinositide 3-kinase

β_i

intrinsic buffering capacity

β_i

intracellular buffering capacity

PBS

phosphate-buffered saline

DMA

5-(N,N-dimethyl)-amiloride
- Received November 12, 1999.
- Revision received December 1, 1999.
The American Society for Biochemistry and Molecular Biology, Inc.