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


CONCLUSIONS
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.
Department of Biochemistry, Chhatrapati Shahuji Maharaj Medical University, Lucknow 226003, India.
E
E
Madan
R
R
Gogna
P
P
Kuppusamy
M
M
Bhatt
U
U
Pati
A A
AA
Mahdi
D051017:Apoptosis Regulatory Proteins; D059447:Cell Cycle Checkpoints / Q000187:drug effects / Q000235:genetics*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism; D050687:E2F1 Transcription Factor / Q000235:genetics* / Q000378:metabolism; D016193:G1 Phase / Q000187:drug effects / Q000235:genetics; D015870:Gene Expression / Q000187:drug effects; D006019:Glycolysis / Q000187:drug effects / Q000235:genetics; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics* / Q000378:metabolism; D007624:KB Cells; D010744:Phosphoric Monoester Hydrolases; D010766:Phosphorylation / Q000187:drug effects / Q000235:genetics; D054730:Protein Interaction Domains and Motifs / Q000187:drug effects / Q000235:genetics; D019572:Retinal Neoplasms / Q000235:genetics* / Q000378:metabolism; D012175:Retinoblastoma / Q000235:genetics* / Q000378:metabolism; D016196:S Phase / Q000187:drug effects / Q000235:genetics; D013629:Tamoxifen / Q000494:pharmacology; D016159:Tumor Suppressor Protein p53 / Q000235:genetics* / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050687:E2F1 Transcription Factor; D047908:Intracellular Signaling Peptides and Proteins; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D013629:Tamoxifen; D018844:Cyclin-Dependent Kinases; D010744:Phosphoric Monoester Hydrolases; C512708:TIGAR protein, human