ABSTRACT
The ends of eukaryotic chromosomes are specialized sequences, called telomeres comprising tandem repeats of simple DNA sequences. Those sequences are essential for preventing aberrant recombination and protecting genomic DNA against exonucleolytic DNA degradation. Telomeres are maintained at a stable length by telomerase, an RNA-dependent DNA polymerase. Recently, human telomerase has been recognized as a unique diagnostic marker for human tumors and is potentially a highly selective target for antitumor drugs. In this study, we have examined the major factors affecting the catalytic activity and processivity of human telomerase. Specifically, both the catalytic activity and processivity of human telomerase were modulated by temperature, substrate (dNTP and primer) concentration, and the concentration of K+. The catalytic activity of telomerase increased as temperature (up to 37 degrees C), concentrations of dGTP, primer, and K+ were increased. However, the processivity of human telomerase decreased as temperature, primer concentration, and K+ were increased. Our results support the current model for human telomerase reaction and strengthen the hypothesis that a G-quadruplex structure of telomere DNA plays an important role in the regulation of the telomerase reaction.
Subject(s)
Protein Processing, Post-Translational , Telomerase/chemistry , Telomerase/metabolism , Catalysis , DNA Primers/chemistry , DNA Primers/metabolism , Deoxyguanine Nucleotides/chemistry , Deoxyguanine Nucleotides/metabolism , Enzyme Activation/genetics , HeLa Cells , Humans , Models, Biological , Models, Chemical , Potassium/chemistry , Potassium/metabolism , Protein Processing, Post-Translational/genetics , Telomerase/geneticsABSTRACT
The major isoform of hGH is a polypeptide of 191 amino acids. Human GH1-43 is an amino terminal segment of hGH1-191 which comprises the first 43 amino acids. This peptide is a potent regulator of glucose homeostasis. To facilitate our understanding of the physiological regulation of hGH1-43 an assay to measure its levels in biological fluids and extracts is needed. This communication describes the development of anti-hGH1-43 monoclonal antibodies and their use in the development of an indirect competitive ELISA for the quantification of hGH1-43. Hybridomas were produced by the fusion of FOX-NY myeloma cells with spleen cells taken from a mouse immunized with hGH1-43. The hybridomas were screened for production of antibodies to hGH1-43 by antibody capture ELISA. Hybridomas which produced antibodies reactive to hGH1-43 were cloned by limiting dilution. Three monoclonal hybridomas, CCL-1, CCL-2, and CCL-3 were subsequently obtained. These hybridomas secreted antibodies that were highly reactive towards hGH1-43 but minimally reactive towards hGH1-191. The isotypes of the mAbs secreted by CCL-1, CCL-2 and CCL-3 were all IgG1 kappa as shown by isotype specific antibody capture analysis. An indirect competitive ELISA with a detection limit that ranged from 1 to 10 ng/ml was developed using mAbs from monoclonal hybridoma CCL-3. Dose-response curves for competing hGH1-191, hPRL, and hPL indicated minimal cross-reactivity of mAbs with these hormones and conversely, a high degree of specificity for hGH1-43. Dose-response curves for dilutions of human serum and pituitary extract were parallel to the standard. The availability of a sensitive assay for the measurement of hGH1-43 will help us answer questions regarding the biosynthesis, regulation of secretion, and role of hGH1-43 in the control of glucose homeostasis.
