TIGAR Enhanced Free Ca2+ Concentration in Hepatocellular Carcinoma Cells to Accelerate the Sustained Proliferation and Drug Resistance

Abstract

Background: To study the role of TP53-induced glycolysis and apoptosis regulator (TIGAR) in hepatocellular carcinoma (HCC) and drug resistance.Methods: HCC cells (HepG2 and SMMC7721) were used in this study. Fura 2-AM was used to assess cytosolic free Ca2+ concentrations ([Ca2+]i) within the two HCC cell lines. Nimodipine (NMDP), a Ca2+ antagonist, was used to reduce cytosolic [Ca2+]i level. Proliferation of HCC was measured using cell counting kit-8 (CCK-8). The roles of TIGAR and Ca2+ in drug resistance of HCC cells were assessed using epirubicin (Epi), 5-fluorouracil (5-FU), or cisplatinum (DDP).Results: Knockdown of TIGAR significantly suppressed cell viability, reduced [Ca2+]i, restrained protein expression of Ca2+-activated cysteine proteinases (Calpain1 and 2), as well as blocked the activation of nuclear factor kappa B (NF-κB) through an increase of cytoplasmic NF-κB and reduction of nuclear NF-κB. However, overexpression of TIGAR (oeTIGAR) resulted in the opposite. Evidence also shows that oeTIGAR suppressed the sensitivity of HCC to Epi, which was retarded by NMDP as an additional treatment. TIGAR interference could enhance the sensitivity of HCCs with high TIGAR expression to drugs.Conclusions: TIGAR promoted HCC progression and induced drug resistance, and the mechanism involved was [Ca2+]i-mediated activation of Calpain 1 and 2 and NF-κB signaling.