Non-competitive cyclic peptides for targeting enzyme-substrate complexes.

Affinity reagents are of central importance for selectively identifying proteins and investigating their interactions. We report on the development and use of cyclic peptides, identified by mRNA display-based RaPID methodology, that are selective for, and tight binders of, the human hypoxia inducible factor prolyl hydroxylases (PHDs) - enzymes crucial in hypoxia sensing. Biophysical analyses reveal the cyclic peptides to bind in a distinct site, away from the enzyme active site pocket, enabling conservation of substrate binding and catalysis. A biotinylated cyclic peptide captures not only the PHDs, but also their primary substrate hypoxia inducible factor HIF1-α. Our work highlights the potential for tight, non-active site binding cyclic peptides to act as promising affinity reagents for studying protein-protein interactions.

Utility of VS38c in the diagnostic and prognostic assessment of osteosarcoma and other bone tumours/tumour-like lesions.

BACKGROUND: VS38c is a monoclonal antibody that recognises a rough endoplasmic reticulum (rER) intracellular antigen termed cytoskeleton-linking membrane protein 63. rER is typically found in viable tumour cells and is abundant in osteosarcoma cells. The aim of this study was to determine the diagnostic and prognostic utility of VS38c in the histological assessment of osteosarcoma and other bone tumours/tumour-like leisons. METHODS: Immunohistochemical staining with VS38c was carried out on formalin-fixed specimens of osteosarcoma (pre/post-chemotherapy) and a wide range of benign and malignant bone lesions. In addition, VS38c staining of cultures of MG63 and Sa0S2 osteosarcoma cell cultures. (±cisplatin and actinomycin D-treatment) was analysed. RESULTS: VS38c strongly stained tumour cells in all low-grade and high-grade osteosarcomas and in undifferentiated sarcomas and high-grade chondrosarcomas. There was little or no VS38c staining of low-grade chondrosarcomas or chordomas and variable staining of Ewing sarcomas. Osteoblasts in benign bone-forming tumours and mononuclear stromal cells in chondroblastomas, giant cell tumours and non-ossifying fibromas strongly stained for VS38c. VS38c staining was absent in cisplatin and actinomycin D treated Sa0S2 and MG63 cells. In specimens of osteosarcoma post-neoadjuvant therapy, VS38c staining was absent in most morphologically necrotic areas of tumor although some cells with pyknotic nuclei stained for VS38c in these areas. Most tumour cells exhibiting atypical nuclear forms were not stained by VS38c. CONCLUSIONS: Our findings show that VS38c is a sensitive but not specific diagnostic marker of osteosarcoma. Staining with VS38c identifies viable osteosarcoma cells, a feature which may be useful in the assessment of percentage tumour necrosis post-neoadjuvant chemotherapy.

Dentine matrix protein 1 (DMP-1) is a marker of bone formation and mineralisation in soft tissue tumours.

Dentine matrix protein 1 (DMP-1) is a non-collagenous matrix protein found in dentine and bone. It is highly expressed by osteocytes and has been identified in primary benign and malignant osteogenic bone tumours. Bone formation and matrix mineralisation are seen in a variety of benign and malignant soft tissue tumours and tumour-like lesions, and in this study, we analysed immunohistochemically the DMP-1 expression in a wide range of soft tissue lesions (n = 254) in order to assess whether DMP-1 expression is useful in the histological diagnosis of soft tissue tumours. Matrix staining of DMP-1 was seen in all cases of myositis ossificans, fibro-osseous tumour of the digits, extraskeletal soft tissue osteosarcoma and in most cases of ossifying fibromyxoid tumour. DMP-1 was also noted in dense collagenous connective tissue of mineralising soft tissue lesions such as tumoural calcinosis, dermatomyositis and calcific tendinitis. DMP-1 was expressed in areas of focal ossification and calcification in synovial sarcoma and other soft tissue tumours. With few exceptions, DMP-1 was not expressed in other benign and malignant soft tissue tumours. Our findings indicate that DMP-1 is a matrix marker of bone formation and mineralisation in soft tissue tumours. DMP-1 expression should be particularly useful in distinguishing extraskeletal osteosarcoma and ossifying fibromyxoid tumour from other sarcomas and in identifying areas of osteoid/bone formation and mineralisation in soft tissue tumours.

The role of calcium and nicotinic acid adenine dinucleotide phosphate (NAADP) in human osteoclast formation and resorption.

Osteoclasts are specialised bone resorbing cells which form by fusion of circulating mononuclear phagocyte precursors. Bone resorption results in the release of large amounts of calcium into the extracellular fluid (ECF), but it is not certain whether changes in extracellular calcium concentration [Ca(2+)]e influence osteoclast formation and resorption. In this study, we sought to determine the effect of [Ca(2+)]e and NAADP, a potent calcium mobilising messenger that induces calcium uptake, on human osteoclast formation and resorption. CD14+ human monocytes were cultured with M-CSF and RANKL in the presence of different concentrations of calcium and NAADP and the effect on osteoclast formation and resorption evaluated. We found that the number of TRAP+ multinucleated cells and the extent of lacunar resorption were reduced when there was an increase in extracellular calcium and NAADP. This was associated with a decrease in RANK mRNA expression by CD14+ cells. At high concentrations (20 mM) of [Ca(2+)]e mature osteoclast resorption activity remained unaltered relative to control cultures. Our findings indicate that osteoclast formation is inhibited by a rise in [Ca(2+)]e and that RANK expression by mononuclear phagocyte osteoclast precursors is also [Ca(2+)]e dependent. Changes in NAADP also influence osteoclast formation, suggesting a role for this molecule in calcium handling. Osteoclasts remained capable of lacunar resorption, even at high ECF [Ca(2+)]e, in keeping with their role in physiological and pathological bone resorption.