Short-term treatment with glucosamine hydrochloride specifically downregulates hypoxia-inducible factor-1α at the protein level in YD-8 human tongue cancer cells

Hypoxia-inducible factor-1 (HIF-1) is a tumor angiogenic transcription factor composed of an α and β subunit. We investigated the effect of glucosamine hydrochloride (GS-HCl) on the expression of HIF-1α and HIF-1β in serumtreated YD-8 human tongue cancer cells. While long-term (24 h) treatment with GS-HCl strongly repressed the expression of HIF-1α and HIF-1β at both the protein and mRNA levels, short-term (4 h) GS-HCl treatment inhibited HIF-1α at the protein level. Short-term GS-HCl treatment also decreased phosphorylation of p70S6K and S6, translation-related proteins. However, the results of subsequent pharmacological inhibition and protein stability analyses indicated that HIF-1α protein downregulation induced by short-term GS-HCl treatment was not through modulation of the mTOR/p70S6K/S6 signaling pathways, the 26S proteasomal and lysosomal activities and HIF-1α protein stability. Importantly, our further analyses identified that HIF-1α protein downregulation induced by short-term GS-HCl treatment was blunted by exogenous administration of the citric acid cycle metabolites citrate and 2-oxoglutarate, but not the glycolytic end byproducts pyruvate and lactate. These findings demonstrate firstly that short-term GS treatment selectively downregulates HIF-1α at the protein level in YD-8 cells via interference of production of the citric acid cycle metabolites. It is proposed that short-term GS-HCl exposure may be applied for the treatment of oral tumors with high expression of HIF-1α.