An Active Form of Sphingosine Kinase-1 Is Released in the Extracellular Medium as Component of Membrane Vesicles Shed by Two Human Tumor Cell Lines

Salvatrice Rigogliuso,Monica Salamone,Paola Bruni,Simona Taverna,Maria Letizia Vittorelli,Donata Cassarà,Chiara Donati

doi:10.1155/2010/509329

Salvatrice Rigogliuso, Monica Salamone + Show 5 more

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https://doi.org/10.1155/2010/509329

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Abstract

Expression of sphingosine kinase-1 (SphK-1) correlates with a poor survival rate of tumor patients. This effect is probably due to the ability of SphK-1 to be released into the extracellular medium where it catalyzes the biosynthesis of sphingosine-1-phosphate (S1P), a signaling molecule endowed with profound proangiogenic effects. SphK-1 is a leaderless protein which is secreted by an unconventional mechanism. In this paper, we will show that in human hepatocarcinoma Sk-Hep1 cells, extracellular signaling is followed by targeting the enzyme to the cell surface and parallels targeting of FGF-2 to the budding vesicles. We will also show that SphK-1 is present in a catalitycally active form in vesicles shed by SK-Hep1 and human breast carcinoma 8701-BC cells. The enzyme substrate sphingosine is present in shed vesicles where it is produced by neutral ceramidase. Shed vesicles are therefore a site for S1P production in the extracellular medium and conceivably also within host cell following vesicle endocytosis.

Highlights

Malignant tumors have the remarkable ability to adapt their stromal environment to their benefit
As can more clearly be seen in cells transiently transfected with GFPSphK-1 (Figure 2), both sphingosine kinase-1 (SphK-1) and β1 integrin seem to be more dense in specific areas of the plasma membrane, and clustering appears to occur in areas of the cell membrane from which vesicles are released (Figure 2(d))
Shed vesicles have been shown to induce angiogenesis using a variety of mechanisms including the action of proteins such 20 μm (a) as FGF-2, VEGF, angiogenin, IL-6, IL-8, and TIMPs, and lipid molecules such as sphingomyelin

Summary

Introduction

Malignant tumors have the remarkable ability to adapt their stromal environment to their benefit. They alter the surrounding extracellular matrix and modify normal cell behavior to facilitate tumor cell growth, invasion, immune evasion, and angiogenesis [1]. Most of these effects are mediated by the release of small vesicles from the tumor cells into the extracellular medium. The vesicle membranes are selectively enriched in some components including MMP9 [7] and other proteolytic enzymes [4, 6], together with β1 Integrin and class I HLA molecules [7]. Vesicles use several mechanisms to contribute to tumor escape from immune reactions [11,12,13,14,15,16]

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