¹Department of Pharmacology and Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seoul, Korea

Correspondence: Dr JY Kim, PhD, Department of Pharmacology, Yonsei University College of Medicine, 250 Sungsan-ro, Seoul 120-752, Korea. E-mail: jooyoungkim@yuhs.ac

²These authors contributed equally to this work.

Received 28 October 2008; Revised 21 April 2009; Accepted 21 April 2009; Published online 8 June 2009.

Abstract

The formation of a pH gradient, which is characterized by intracellular alkalinization and extracellular acidification, plays a key role in the growth and metastasis of tumor cells. However, the underlying mechanisms of alkalinization-induced cell growth are not known. In this study, we investigated the roles of eukaryotic translation elongation factor 1 (eEF1A) in alkalinization-induced cell growth. In all cell lines tested (NIH3T3, HEK293, and HeLa), cell growth was affected by the modulation of intracellular pH. In general, weak intracellular alkalinization produced increased cell growth, whereas intracellular acidification resulted in decreased cell growth. It is interesting to note that portions of actin-bound eEF1A proteins were gradually reduced from acidic to alkaline conditions, suggesting an increase in levels of functionally active, free-form eEF1A. Over-expression of eEF1A caused increased cell growth in HeLa cells. It should be noted that dissociation of eEF1A from actin by transfection with the actin-binding domain deleted eEF1A construct further increased cell growth under acidic conditions, whereas most of the intact eEF1A was bound to actin. Conversely, knockdown of eEF1A by treatment with eEF1A1 and eEF1A2 siRNAs nullified the effects of alkalinization-induced cell growth. The above findings suggest that an increase in free-form eEF1A under alkaline conditions plays a critical role in alkalinization-induced cell growth.