ABSTRACT
Fatty acids bound to albumin have been reported to be involved in various responses in renal proximal tubular cells following albumin overload, leading to progression of tubulointerstitial damage in the kidneys. In addition, it has been reported that prostaglandin E2 (PGE2) plays an important role in nephrotoxicity. The aim of this study was to examine whether albumin-bound fatty acids induce PGE2 production in human renal proximal tubular epithelial cell line HK-2. Fatty acid-bearing human serum albumin increased PGE2 release in the culture medium in concentration-dependent and time-dependent manners, but fatty acid-depleted albumin had no effect on PGE2 production. Next, we investigated the effect of arachidonic acid, a precursor of eicosanoids, on PGE2 production. Arachidonic acid with fatty acid-free albumin significantly enhanced the release of PGE2 into the medium in a concentration-dependent manner. Furthermore, we examined the effect of arachidonic acid on mRNA expression of hypoxia inducible factor-1α (HIF-1α). Arachidonic acid increased HIF-1α mRNA expression in a concentration-dependent manner. These findings suggest that fatty acids, at least in part arachidonic acid, bound to albumin increase PGE2 production and expression of HIF-1α mRNA and protein, possibly resulting in various cell responses induced by albumin overload.
Subject(s)
Dinoprostone/metabolism , Fatty Acids/metabolism , Kidney Tubules, Proximal/metabolism , Serum Albumin, Human/metabolism , Cell Line , Humans , Kidney Tubules, Proximal/cytology , Protein BindingABSTRACT
We previously reported that fatty acid-bearing albumin but not fatty acid-depleted albumin induces hypoxia-inducible factor-1 (HIF-1) activation in human renal proximal tubular epithelial cell line HK-2. Then, an increase in mRNA expression of peroxisome proliferator-activated receptor gamma (PPARγ) was observed on treatment with fatty acid-bearing albumin but not fatty acid-depleted albumin. The aim of this study was to determine whether a PPARγ agonist, pioglitazone, induces HIF-1 activation or not. Treatment with pioglitazone induced HIF-1α mRNA as well as PPARγ mRNA expression in a concentration dependent manner. In addition, pioglitazone increased HIF-1 target genes such as the mRNAs of glucose transporter 1 (GLUT1) and breast cancer resistance protein (BCRP/ABCG2), in a concentration-dependent manner. Consistent with the increases in GLUT1 and ABCG2 mRNAs, protein expression of GLUT1 and BCRP was increased by pioglitazone. In addition, GLUT inhibitor phloretin-sensitive D-[3H]glucose uptake activity and BCRP inhibitor Ko143-sensitive accumulation of Hoecsht33342, a BCRP substrate, were significantly enhanced by treatment with pioglitazone. These findings suggest that PPARγ activation by pioglitazone leads to HIF-1 protein expression induction followed by changes in HIF-1 target gene expression and protein product activity.
Subject(s)
Epithelial Cells/drug effects , Hypoxia-Inducible Factor 1/metabolism , Pioglitazone/pharmacology , Cells, Cultured , Dose-Response Relationship, Drug , Epithelial Cells/metabolism , Humans , Hypoxia-Inducible Factor 1/genetics , RNA, Messenger/genetics , RNA, Messenger/metabolism , Structure-Activity RelationshipABSTRACT
The human breast cancer resistance protein (BCRP/ABCG2), a member of the ATP-binding cassette transporter family, is a drug transporter restricting absorption and enhancing excretion of many compounds including anticancer drugs. The cis-regulatory elements in the BCRP promoter include a hypoxia response element, i.e., the DNA binding site for hypoxia-inducible factor-1 (HIF-1). In this study, we investigated the effect of cobalt chloride, a chemical inducer of HIF-1α, on the expression and function of BCRP in human renal proximal tubular cell line HK-2. Cobalt chloride treatment significantly increased the mRNA expression of not only glucose transporter 1 (GLUT1), a typical HIF-1 target gene mRNA, but also ABCG2 mRNA in HK-2 cells. The BCRP inhibitor Ko143-sensitive accumulation of BCRP substrates such as Hoechst33342 and mitoxantrone was significantly enhanced by cobalt chloride treatment. In addition, treatment with cobalt chloride significantly increased the Ko143-sensitive accumulation of fluorescein isothiocyanate-labeled methotrexate in HK-2 cells. Furthermore, cobalt chloride treatment attenuated the cytotoxicity induced by mitoxantrone and methotrexate, which might be, at least in part, due to the increase in BCRP-mediated transport activity via HIF-1 activation. These findings indicate that HIF-1 activation protects renal proximal tubular cells against BCRP substrate-induced cytotoxicity by enhancing the expression and function of BCRP in renal proximal tubular cells.
