We identified translationally controlled tumor protein (TCTP) as a Na⁺,K⁺-ATPase binding protein by yeast two-hybrid screening. To understand the functional role of TCTP related to the regulation of Na⁺,K⁺-ATPase activity, TCTP was transiently expressed in HeLa cells. Using ouabain-sensitive ⁸⁶Rb⁺-uptake method and confocal microscopy in living cells, we found that overexpression of TCTP inhibits Na⁺,K⁺-ATPase activity and changes intracellular Na⁺/K⁺ concentration, suggesting that TCTP might act as a cytoplasmic repressor of Na⁺,K⁺-ATPase. It has been reported that Na⁺,K⁺-ATPase inhibition by digitalis glycosides and potassium-deprivation causes hypertension as well as cardiac hypertrophy. Since TCTP functions as a Na⁺,K⁺-ATPase inhibitor like ouabain as shown in our study, we hypothesized that the overexpession of TCTP in the cell might be associated with the pathogenesis of hypertension. Thus, we generated transgenic mice overexpressing TCTP. Following echocardiographic examination, hemodynamic evaluation was performed in closed-chest mice. A 1.4 French high-fidelity micromanometer catheter was inserted into the right carotid artery and advanced retrograde into the LV. Heart weight and LV weight normalized to body weight in the TCTP transgenic mice were not different to those of non-transgenic litters. Although LV size and wall thickness, LV mass, heart rate, fractional shortening and LVEDP was similar in both mice, systolic and diastolic blood pressure was significantly elevated in the TCTP transgenic mice compared to wild-type mice. Our new finding suggests that as a negative regulator of Na⁺,K⁺-ATPase activity, TCTP seems to play a key role in maintaining the cells' ion homeostasis and dysregulation of its gene expression may lead to disease progression, such as hypertension.