guanosine-triphosphate and Bone-Neoplasms

The bisphosphonates (BPs) are well established as the treatments of choice for disorders of excessive bone resorption, including Paget's disease of bone, myeloma and bone metastases, and osteoporosis. There is considerable new knowledge about how BPs work. Their classical pharmacological effects appear to result from two key properties: their affinity for bone mineral and their inhibitory effects on osteoclasts. Mineral binding affinities differ among the clinically used BPs and may influence their differential distribution within bone, their biological potency, and their duration of action. The inhibitory effects of the nitrogen-containing BPs (including alendronate, risedronate, ibandronate, and zoledronate) on osteoclasts appear to result from their inhibition of farnesyl pyrophosphate synthase (FPPS), a key branch-point enzyme in the mevalonate pathway. FPPS generates isoprenoid lipids used for the posttranslational modification of small GTP-binding proteins essential for osteoclast function. Effects on other cellular pathways, such as preventing apoptosis in osteocytes, are emerging as other potentially important mechanisms of action. As a class, BPs share several common properties. However, as with other classes of drugs, there are obvious chemical, biochemical, and pharmacological differences among the various individual BPs. Each BP has a unique profile that may help to explain potential important clinical differences among the BPs, in terms of speed of onset of fracture reduction, antifracture efficacy at different skeletal sites, and the degree and duration of suppression of bone turnover. As we approach the 40th anniversary of the discovery of their biological effects, there remain further opportunities for using their properties for medical purposes.

Topics: Animals; Bone and Bones; Bone Neoplasms; Bone Resorption; Diphosphonates; Guanosine Triphosphate; Humans; Models, Biological; Models, Chemical; Multiple Myeloma; Neoplasm Metastasis; Nitrogen; Osteoclasts; Osteocytes; Osteoporosis; Protein Processing, Post-Translational; T-Lymphocytes; Treatment Outcome

Human mitoribosomes are macromolecular complexes essential for translation of 11 mitochondrial mRNAs. The large and the small mitoribosomal subunits undergo a multistep maturation process that requires the involvement of several factors. Among these factors, GTP-binding proteins (GTPBPs) play an important role as GTP hydrolysis can provide energy throughout the assembly stages. In bacteria, many GTPBPs are needed for the maturation of ribosome subunits and, of particular interest for this study, ObgE has been shown to assist in the 50S subunit assembly. Here, we characterize the role of a related human Obg-family member, GTPBP5. We show that GTPBP5 interacts specifically with the large mitoribosomal subunit (mt-LSU) proteins and several late-stage mitoribosome assembly factors, including MTERF4:NSUN4 complex, MRM2 methyltransferase, MALSU1 and MTG1. Interestingly, we find that interaction of GTPBP5 with the mt-LSU is compromised in the presence of a non-hydrolysable analogue of GTP, implying a different mechanism of action of this protein in contrast to that of other Obg-family GTPBPs. GTPBP5 ablation leads to severe impairment in the oxidative phosphorylation system, concurrent with a decrease in mitochondrial translation and reduced monosome formation. Overall, our data indicate an important role of GTPBP5 in mitochondrial function and suggest its involvement in the late-stage of mt-LSU maturation.

Topics: Bone Neoplasms; Cell Line, Tumor; CRISPR-Cas Systems; Gene Expression Regulation; Gene Knockout Techniques; Guanosine Triphosphate; HEK293 Cells; Humans; Mitochondrial Proteins; Mitochondrial Ribosomes; Monomeric GTP-Binding Proteins; Osteosarcoma; Oxidative Phosphorylation; Protein Interaction Mapping; Ribosomal Proteins; Ribosome Subunits, Large, Eukaryotic

The hormone-sensitive adenylate cyclase system of a cloned bone cell line (UMR-106) derived from a rat osteosarcoma was compared in preparations from cells of early passages (less than 50) and cells maintained in continuous culture for over two years (late passages). Late passage cells showed greater calcitonin (CT)-stimulated adenylate cyclase activity than did early passages, whereas stimulation by PTH and the beta-adrenergic agonist isoproterenol decreased in late passages. Hormone concentrations giving half-maximal stimulation were the same in early and late passages. Stimulation by agents (GTP and fluoride) which act at the stimulatory guanine nucleotide regulatory component (Ns) of adenylate cyclase was equivalent in early and late passages. Forskolin stimulation, which assessed catalytic component (and possibly Ns) activity, was reduced in late passages. These results are consistent with acquisition by cultured UMR-106 cells of CT receptors linked to adenylate cyclase and loss of PTH and beta-adrenergic receptors. Alteration of catalytic component (and/or Ns) function may also occur after long-term culture. Since late passage cells appear dedifferentiated by chromosomal analysis and since cAMP may regulate differentiation, altered hormone-sensitive adenylate cyclase may be a marker for and a potential modulator of differentiation occurring in UMR-106 cells over long periods.

Topics: 1-Methyl-3-isobutylxanthine; Adenylyl Cyclases; Animals; Bone Neoplasms; Calcitonin; Dinoprostone; Fluorides; Guanosine Triphosphate; Hormones; Isoproterenol; Osteosarcoma; Parathyroid Hormone; Rats; Tumor Cells, Cultured