TIGAR induces p53-mediated cell-cycle arrest by regulation of RB–E2F1 complex

Abstract

Background:p53 induces cell-cycle arrest and apoptosis in cancer cells and negatively regulates glycolysis via TIGAR. Glycolysis is crucial for cancer progression although TIGAR provides protection from reactive oxygen species and apoptosis. The relation between TIGAR-mediated inhibition of glycolysis and p53 tumour-suppressor activity is unknown.Methods:RT–PCR, western blot, luciferase and chromatin immunoprecipitation assays were used to study TIGAR gene regulation. Co-IPP was used to determine the role of TIGAR protein in regulating the protein–protein interaction between retinoblastoma (RB) and E2F1. MCF-7 tumour xenografts were utilised to study the role of TIGAR in tumour regression.Results:Our study shows that TIGAR promotes p21-independent, p53-mediated G1-phase arrest in cancer cells. p53 activates the TIGAR promoter only in cells exposed to repairable doses of stress. TIGAR regulates the expression of genes involved in cell-cycle progression; suppresses synthesis of CDK-2, CDK-4, CDK-6, Cyclin D, Cyclin E and promotes de-phosphorylation of RB protein. RB de-phosphorylation stabilises the complex between RB and E2F1 thus inhibiting the entry of cell cycle from G1 phase to S phase.Conclusion:TIGAR mediates de-phosphorylation of RB and stabilisation of RB–E2F1 complex thus delaying the entry of cells in S phase of the cell cycle. Thus, TIGAR inhibits proliferation of cancer cells and increases drug-mediated tumour regression by promoting p53-mediated cell-cycle arrest.

Role of Endoplasmic Reticulum Stress and Unfolded Protein Responses in Health and Diseases

“…Tumor suppressor gene TP53, which is activated during different stressful conditions, plays pivotal role in several biological mechanisms including promotion of cell cycle arrest, senescence and apoptosis, [86][87][88][89][90]. TP53 regulation in ER stress is debatable.…”

SCO2 Induces p53-Mediated Apoptosis by Thr845 Phosphorylation of ASK-1 and Dissociation of the ASK-1–Trx Complex

“…For hypoxic exposure, cells were placed into a humidified chamber maintained at 1.8% O 2 and 5% CO 2 (balance N 2 ) for 24 h, as described previously (18,19,21). The oxygen level in the chamber was monitored with an oxygen analyzer (Vascular Technology).…”

“…p53 cDNA, SCO2 cDNA, p53 small interfering RNA (siRNA), and SCO2 siRNA were purchased from Origene (18,19,(21)(22)(23)(24)(25). Cells were split 2 days before transfection at a density of 5 ϫ 10 5 cells per plate.…”

“…An 80-l cell suspension containing 1 ϫ 10 7 cells was subcutaneously injected into the hind leg of each mouse (18,19). Tumor volumes were monitored weekly by caliper measurement of length, width, and height and were calculated by using the formula for a semiellipsoid (2r 3 /3) (18,19).…”

“…ϩ/ϩ , HCT p53 Ϫ/Ϫ , A-431, and H1299 cells were obtained from ATCC (Manassas, VA) and the National Center for Cell Sciences (Pune, India) (18,19). ASK-1 Ϫ/Ϫ HCT p53 ϩ/ϩ and HCT p53 Ϫ/Ϫ cells were prepared as described previously (23).…”