title: Cellular internalisation of an inositol phosphate visualised by using fluorescent InsP5.
abstract: When applied extracellularly, myo-inositol hexakisphosphate (InsP6 ) and myo-inositol pentakisphosphate (InsP5 ) can inhibit the growth and proliferation of tumour cells. There is debate about whether these effects result from interactions of InsP6 and InsP5 with intracellular or extracellular targets. We synthesised FAM-InsP5 , a fluorescent conjugate of InsP5 that allows direct visualisation of its interaction with cells. FAM-InsP5 was internalised by H1229 tumour cells, a finding that supports earlier reports that externally applied inositol phosphates can-perhaps surprisingly-enter into cells. Close examination of the process of FAM-InsP5 uptake suggests a mechanism of non-receptor-mediated endocytosis, which is blocked at 4 °C and probably involves interaction of the ligand with the glycocalyx. However, our results are difficult to reconcile with antiproliferative mechanisms that require direct interactions of externally applied InsP5 or InsP6 with cytosolic proteins, because internalised FAM-InsP5 appears in lysosomes and apparently does not enter the cytoplasm. Studies using FAM-InsP5 are less difficult and time-consuming than experiments using InsP5 or InsP6 , a factor that allowed us to analyse cellular uptake across a range of human cell types, identifying strong cell-specific differences.
authors: Wolfson Laboratory of Medicinal Chemistry, Department of Pharmacy and Pharmacology, University of Bath, Claverton Down, Bath BA2 7AY (UK).
authors: Andrew M
authors: AM
authors: Riley
authors: Sabine
authors: S
authors: Windhorst
authors: Hong-Yin
authors: HY
authors: Lin
authors: Barry V L
authors: BV
authors: Potter
mesh_terms: D002460:Cell Line; D048429:Cell Size; D004705:Endocytosis; D005456:Fluorescent Dyes / Q000737:chemistry*; D045325:HCT116 Cells; D006801:Humans; D007295:Inositol Phosphates / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D010833:Phytic Acid / Q000737:chemistry; D013696:Temperature
chemical_list: D005456:Fluorescent Dyes; D007295:Inositol Phosphates; C013571:inositol pentaphosphate; D010833:Phytic Acid
keywords: cyclitols; fluorescent probes; inositol; natural products; phytic acid