ABSTRACT
Oxidative stress regulates telomere homeostasis and cellular aging by unclear mechanisms. Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) is a key mediator of many oxidative stress responses, involving GAPDH nuclear translocation and induction of cell death. We report here that GAPDH interacts with the telomerase RNA component (TERC), inhibits telomerase activity, and induces telomere shortening and breast cancer cell senescence. The Rossmann fold containing NAD(+) binding region on GAPDH is responsible for the interaction with TERC, whereas a lysine residue in the GAPDH catalytic domain is required for inhibiting telomerase activity and disrupting telomere maintenance. Furthermore, the GAPDH substrate glyceraldehyde-3-phosphate (G3P) and the nitric oxide donor S-nitrosoglutathione (GSNO) both negatively regulate GAPDH inhibition of telomerase activity. Thus, we demonstrate that GAPDH is regulated to target the telomerase complex, resulting in an arrest of telomere maintenance and cancer cell proliferation.
Subject(s)
Breast Neoplasms/enzymology , Breast Neoplasms/pathology , Cellular Senescence , Glyceraldehyde-3-Phosphate Dehydrogenase (Phosphorylating)/metabolism , RNA/metabolism , Telomerase/metabolism , Breast Neoplasms/genetics , Cell Line, Tumor , Cellular Senescence/drug effects , Female , Gene Expression Regulation, Neoplastic/drug effects , Glyceraldehyde 3-Phosphate/pharmacology , Glyceraldehyde-3-Phosphate Dehydrogenase (Phosphorylating)/chemistry , Glyceraldehyde-3-Phosphate Dehydrogenase (Phosphorylating)/genetics , Green Fluorescent Proteins/metabolism , Humans , NAD/pharmacology , Protein Binding/drug effects , Protein Structure, Tertiary , RNA/antagonists & inhibitors , RNA/chemistry , S-Nitrosoglutathione/pharmacology , Structure-Activity Relationship , Telomerase/antagonists & inhibitors , Telomerase/chemistry , Telomere Shortening/drug effects , Telomere Shortening/geneticsABSTRACT
Telomeres are the termini of linear chromosomes. They are composed of DNA and DNA-binding proteins critical for maintaining chromosome integrity and cellular function. Telomere binding proteins regulate the structure and function of telomeres through the formation of different complexes with telomeric DNA. Double- and single-stranded telomeric DNA binding protein complexes have shared and unique functions that regulate telomere homeostasis. Recent studies have shown that telomerase interacts with several telomere-binding protein complexes including shelterin, CST, DNA-dependent protein kinase (DNA-PK) and MRN. The present review describes the recognised telomere-binding protein complexes, sub-complex exchanges and inter-complex molecular interactions. It also discusses the evidence suggesting that telomerase reverse transcriptase (TERT) switches between different complexes. Studies of the telomere protein inter-complex interactions and the switching of components between complexes provide insight into their fundamental roles of programming telomere length and configuration, and thus cell proliferative potential.
Subject(s)
Telomerase/physiology , Telomere/metabolism , Alternative Splicing , Animals , DNA/metabolism , DNA-Activated Protein Kinase/metabolism , Humans , Multiprotein Complexes/metabolism , Saccharomyces cerevisiae Proteins/metabolism , Shelterin Complex , Telomere-Binding Proteins/metabolismABSTRACT
Telomere maintenance is critical in tumor cell immortalization. Here, we report that the cytokine bone morphogenetic protein-7 (BMP7) inhibits telomerase activity that is required for telomere maintenance in cervical cancer cells. Application of human recombinant BMP7 triggers a repression of the human telomerase reverse transcriptase (hTERT) gene, shortening of telomeres, and hTERT repression-dependent cervical cancer cell death. Continuous treatment of mouse xenograft tumors with BMP7, or silencing the hTERT gene, results in sustained inhibition of telomerase activity, shortening of telomeres, and tumor growth arrest. Overexpression of hTERT lengthens telomeres and blocks BMP7-induced tumor growth arrest. Thus, BMP7 negatively regulates telomere maintenance, inducing cervical tumor growth arrest by a mechanism of inducing hTERT gene repression.
Subject(s)
Bone Morphogenetic Protein 7/pharmacology , Telomerase/antagonists & inhibitors , Telomere/drug effects , Uterine Cervical Neoplasms/drug therapy , Animals , Apoptosis/drug effects , Dose-Response Relationship, Drug , Female , HeLa Cells , Humans , Mice , Mice, Inbred BALB C , Neoplasm Transplantation , Telomerase/genetics , Transplantation, Heterologous , Uterine Cervical Neoplasms/genetics , Uterine Cervical Neoplasms/pathologyABSTRACT
Telomerase is a ribonucleoprotein complex that maintains chromosomal telomere homeostasis and underlies continuous renewal of stem cells and immortalization of neoplastic cells. Telomerase is down-regulated during cell differentiation, but the mechanisms of down-regulation are largely unknown. Here, we examined roles of mitogen-activated protein (MAP) kinase and phosphatidylinositol-3 (PI3) kinase signalling pathways in telomerase down-regulation triggered by nerve growth factor (NGF), and the role of telomerase down-regulation in NGF-induced neural differentiation in PC12 cells. We report that NGF-induced telomerase down-regulation requires MAP kinase signalling. While mutations of all putative Akt phosphorylation sites in telomerase reverse transcriptase (TERT) has no effect on telomerase activity, inhibition of MAP kinase signalling by PD98059 or U0126 abolishes NGF-induced telomerase down-regulation in a concentration-dependent manner. Reversal of NGF-induced telomerase down-regulation by TERT overexpression does not prevent NGF-induced neural differentiation. Down-regulation of telomerase by silencing TERT gene expression does not trigger cell differentiation in the absence of NGF, nor enhances NGF-induced differentiation. Thus, telomerase, withdraws by a mechanism at TERT gene transcription level involving MAP kinase signalling while cells cease proliferation and undergo differentiation. The withdrawal of telomerase is not required to mediate NGF-induced PC12 cell differentiation and re-establishment of telomerase activity at significant levels does not inhibit differentiation.
