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Cellular Internalisation of an Inositol Phosphate Visualised by Using Fluorescent InsP 5
Author(s) -
Riley Andrew M.,
Windhorst Sabine,
Lin HongYin,
Potter Barry V. L.
Publication year - 2014
Publication title -
chembiochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.05
H-Index - 126
eISSN - 1439-7633
pISSN - 1439-4227
DOI - 10.1002/cbic.201300583
Subject(s) - microbiology and biotechnology , inositol , intracellular , extracellular , cytosol , endocytosis , biochemistry , inositol phosphate , cytoplasm , biology , inositol trisphosphate , biophysics , receptor , chemistry , enzyme
When applied extracellularly, myo ‐inositol hexakisphosphate (InsP 6 ) and myo ‐inositol pentakisphosphate (InsP 5 ) can inhibit the growth and proliferation of tumour cells. There is debate about whether these effects result from interactions of InsP 6 and InsP 5 with intracellular or extracellular targets. We synthesised FAM‐InsP 5 , a fluorescent conjugate of InsP 5 that allows direct visualisation of its interaction with cells. FAM‐InsP 5 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‐InsP 5 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 InsP 5 or InsP 6 with cytosolic proteins, because internalised FAM‐InsP 5 appears in lysosomes and apparently does not enter the cytoplasm. Studies using FAM‐InsP 5 are less difficult and time‐consuming than experiments using InsP 5 or InsP 6 , a factor that allowed us to analyse cellular uptake across a range of human cell types, identifying strong cell‐specific differences.