The aim of this study was to investigate the effect of human serum albumin (HSA) overload on the expression of the transcription factor hypoxia-inducible factor-1 alpha (HIF-1 alpha) in human renal proximal tubular cell line HK-2. First, the cell viability and cytotoxic activity were examined to assess the cellular conditions in HK-2 cells with HSA treatment employed in this study. HSA treatment for 48 h decreased the cell viability and increased the leakage of lactate dehydrogenase (LDH) into the medium in a concentration-dependent manner, but the toxicity was relatively mild. Western Blot analysis revealed that HSA treatment induced the expression of HIF-1 alpha protein in a concentration-dependent manner without a change in beta-actin protein expression. Confocal microscopy analysis revealed that HIF-1 alpha protein was predominantly localized in the nucleus but was also observed in the cytoplasm. The HIF-1 target gene mRNAs, glucose transporter 1 and glyceraldehyde 3-phosphate dehydrogenase, were up-regulated by HSA treatment, leading to the increases in the protein expression levels. In addition, the mRNA of HIF-1 alpha was increased by HSA treatment. In conclusion, albumin loading induces HIF-1 alpha in HK-2 cells, resulting in the increases in the expression of proteins of its target genes. (C) 2013 Elsevier Inc. All rights reserved.