Cellular Internalisation of an Inositol Phosphate Visualised by Using Fluorescent InsP5. Issue 1 (6th December 2013)

• Record Type: Journal Article
• Authors: Riley, Andrew M.; Windhorst, Sabine; Lin, Hong‐Yin; Potter, Barry V. L.
• Is Part Of: Chembiochem. Volume 15:Issue 1(2014)
• Page Start: 57
• Page End: 67
• Publication Date: 2013-12-06
• Subjects: Biochemistry -- Periodicals; Molecular biology -- Periodicals; Pharmaceutical chemistry -- Periodicals; 572
• DOI: 10.1002/cbic.201300583
• Languages: English
• ISSNs: 1439-4227

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>When applied extracellularly, <italic>myo</italic>‐inositol hexakisphosphate (InsP<sub>6</sub>) and <italic>myo</italic>‐inositol pentakisphosphate (InsP<sub>5</sub>) can inhibit the growth and proliferation of tumour cells. There is debate about whether these effects result from interactions of InsP<sub>6</sub> and InsP<sub>5</sub> with intracellular or extracellular targets. We synthesised FAM‐InsP<sub>5</sub>, a fluorescent conjugate of InsP<sub>5</sub> that allows direct visualisation of its interaction with cells. FAM‐InsP<sub>5</sub> 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<sub>5</sub> 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<sub>5</sub> or InsP<sub>6</sub> with cytosolic proteins, because internalised FAM‐InsP<sub>5</sub> appears in lysosomes and apparently does not enter the cytoplasm. Studies using FAM‐InsP<sub>5</sub> are less difficult and time‐consuming than experiments using InsP<sub>5</sub> or InsP<sub>6</sub>, a factor that allowed us to analyse cellular uptake across a range of human cell types, identifying strong cell‐specific differences.</p> </abstract>